Metrological and quality concepts in analytical chemistry (IUPAC Recommendations 2021)

2.1 analytical chemistry

Scientific discipline that develops and applies strategies, instruments, and procedures to obtain information on the composition and nature of matter in space and time.

1. Note 1: The definition was coined by the Working Party on Analytical Chemistry (WPAC) of the Federation of European Chemical Societies (FECS) and is known as the “Edinburgh Definition” [10].

2. Note 2: The term “analytical science” was coined in 1998 to emphasize the impact of informatics on analytical chemistry [11].

3. [10]. See also: chemical analysis.

2.2 chemical analysis

Application of analytical chemistry.

1. [10].

2.3 qualitative analysis

Examination [12] of nominal properties [VIM 1.30] in analytical chemistry.

1. Note 1: Qualitative analysis is used to detect and establish the identity of chemical substances and species.

2. Identification of heroin (diacetylmorphine) in a sample of white powder seized by the police.

3. Note 2: Qualitative analysis should not be related to ordinal quantity [VIM 1.26] or unitary quantity.

2.4 quantitative analysis

Measurement in analytical chemistry.

1. Quantitative analysis is used to obtain quantity values [VIM 1.19] for ordinal quantities [VIM 1.26] and unitary quantities.

Entry replaces recommendation in [13] p 1701.

3.5 additive matrix effect

Matrix effect that is independent of the measured quantity value [VIM 2.10] of the measurand.

1. Note 1: An additive matrix effect affects the intercept, not the slope of a linear calibration curve.

2. Note 2: The effect is sometimes termed “translational matrix effect” or “background interference” [14].

3. An additive matrix effect that originates from a missing or flawed blank correction [15].

4. The measurement of plutonium mass concentration using a K-edge densitometer in the presence of a uranium admixture. The presence of uranium causes a large additive matrix effect [16].

3.6 aliquot

specimen

Portion of a material assumed to be taken with negligible sampling error [17].

1. An aliquot of an analytical sample is subjected to chemical analysis by chromatography.

2. Note 1: The concept is usually applied to fluids. It can also be used for sufficiently homogeneous solids such as powders. See material homogeneity.

Entry replaces recommendation in [18] p 1206. See also: sample.

3.7 analyte

Component specified in a measurand.

1. The term “analyte”, or the name of a chemical substance or one of its components, is sometimes used for ‘measurand’. This usage is erroneous because these terms do not refer to quantities [VIM 1.1] as it is required for the concept ‘measurand’. See also: Note 4 to measurand.

2. A component to be identified by examination should not be termed analyte but ‘examinand’ [12].

Entry replaces recommendation in [19] p 1660.

3.8 analytical function

See: calibration function.

3.9 analytical run

run

Set of measurements of the same quantity [VIM 1.1] performed under repeatability conditions of measurement.

1. Note: An analytical run may comprise measurements on one or more reference materials, blank materials, quality control materials, and analytical samples.

2. [20].

3.10 analytical sample

Sample, taken and, if need be, prepared from a laboratory sample, portions of which are subject to chemical analysis.

1. Note 1: The analytical sample can be considered to be the combination of an analyte and a matrix.

2. Note 2: A portion of the analytical sample may be termed an aliquot if it is taken with negligible sampling error [17].

3. [18].

3.11 background indication

Indication [VIM 4.1] obtained from a phenomenon, body, or substance similar to the one under investigation but for which a quantity [VIM 1.1] of interest is supposed not to be present or is not contributing to the indication.

1. [VIM 4.2].

2. Note: In VIM 4.2, this concept is termed “blank indication” with “background indication” as an alternate term. However, since blank indication refers to the explicit use of a blank material in analytical chemistry, it should be distinguished from the concept ‘background indication’.

3. [9] p 44 of section 18.

3.12 batch

Material which is known or assumed to be produced under uniform conditions.

1. Note: Some vocabularies assume “lot” and “batch” to be synonymous. The distinction made here with respect to the knowledge of production history permits a lot to consist of one or more batches and is useful in interpreting the results of chemical analysis.

2. [18] entry 2.2.3.

3.13 blank correction

Step in a measurement procedure in which the effect of a blank indication is removed from an indication [VIM 4.1].

1. The blank indication and the indication must be of the same kind of quantity [VIM 1.2].

2. A blank indication may be subtracted from an indication, or, in the case of a transmittance measurement, the indication is divided by the blank indication.

3.14 blank indication

Indication [VIM 4.1] obtained from a sample of blank material under the measurement conditions for the measurand.

1. In VIM 4.2, “background indication” is given as an alternate term for “blank indication”. However, the terms refer to different concepts in [9] p 44 of section 18.

Entry replaces recommendation in [19] p 1662, [21] p 2167.

3.15 blank material

blank

Material which contains no, or as little as possible, of the analyte of interest used in measurement to establish a blank indication.

1. Note 1: Testing, processing, and measurement of blank materials are nearly always an essential part of chemical analysis and may be part of quality assurance and quality control. See [22].

2. Note 2: The concept may be extended to more than one analyte.

3. Note 3: Terms such as “solvent blank”, “reagent blank”, or “matrix blank” are often used to specify the type of blank material.

4. Note 4: The term “procedure blank” is often used to denote a material that is carried through the entire measurement procedure. Terms such as “field blank”, “calibration blank”, and “instrument blank” refer to materials handled in specific parts of the measurement procedure.

5. Note 5: A blank material to which a relevant component has been added is often termed “spiked blank” or “fortified blank”. Compare spike, internal standard, and measurement procedure with standard addition.

6. Note 6: If the term “blank” is used, for example, to denote blank indication or the related blank value or blank correction, this must be clarified by the context.

7. [20, 22].

3.16 blank value

Measured quantity value [VIM 2.10] obtained by application of the calibration function to the blank indication.

1. The concepts ‘blank value’ and ‘blank indication’ should not be confused.

3.17 calibration certificate

Document issued by a technically competent organization providing information about a calibration [VIM 2.39].

1. The document may include a statement describing the calibration procedure and the calibrators [VIM 5.12] (calibrants) applied along with the calibration curve, calibration diagram [VIM 4.30], or other presentations of the calibration.

2. Calibration certificates are often valid for a stated period of time, although this is not stipulated in ISO/IEC 17025 [23].

3. The authority of the organization issuing the document comes from its demonstrated technical competence.

3.18 calibration curve

Expression of the relation between indication [VIM 4.1] and corresponding measured quantity value [VIM 2.10].

1. Note 1: A calibration curve expresses a one-to-one relation that does not supply a measurement result [VIM 2.9] as it bears no information about the measurement uncertainty [VIM 2.26].

2. [VIM 4.31].

3. Note 2: A calibration curve is usually shown in the form of a smooth curve interpolating the data points.

4. Note 3: The term “response curve” is sometimes used for a concept having the same or broader meaning.

5. Note 4: In the VIM calibration diagram, [VIM 4.30] is defined as “Graphical expression of the relation between indication and corresponding measurement result”. A calibration diagram allows measurement uncertainty to be represented in it and so differs from a calibration curve.

3.19 calibration function

Presentation of calibration curve by a mathematical function.

1. A calibration function is established by fitting a mathematical function to the data from the first step of calibration [VIM 2.39] using the measured quantity values provided by measurement standards [VIM 5.1] as input variables to calculate the expected indication. A calibration function bears no information about measurement uncertainty [VIM 2.26]. See also Note 1 to linearity of calibration and Note 2 to measurement procedure with standard addition.

2. Mathematical analysis of the fit of a calibration function may give a contribution to an uncertainty budget [VIM 2.33] for a measured quantity value obtained from the calibration.

3. The inverse of the calibration function, often termed “analytical function”, is applied on an observed indication to attribute a measured quantity value. This corresponds to the second step described in the definition of calibration.

Entry replaces recommendation in [13] p 1703.

3.20 calibration interval

Time period between calibrations [VIM 2.39] over which the performance of the measuring system [VIM 3.2] may be expected to meet specified requirements.

1. Guidelines for the determination of calibration intervals of measuring systems are given in ILAC-G24 [24].

2. ISO 14532 refers to a period “between routine calibrations” [25].

3.21 certified property value

certified value

Property value of a reference material, accompanied by statements of associated uncertainty and traceability and identified as a certified property value in the reference material certificate.

1. Note: In this definition, “traceability” covers both metrological traceability [VIM 2.41] of a measurement result [VIM 2.9] and examination traceability [12] but not object traceability. Similarly, “uncertainty” covers measurement uncertainty [VIM 2.26] and examination uncertainty [12].

2. [2]. See also: non-certified property value.

3.22 chemical purity

purity

Mass (amount of substance or number of entities) of a specified component divided by the mass (amount of substance or number of entities, respectively) of the system.

1. Purity is usually related to a major component. The other components are termed “impurities”.

2. The quantity [VIM 1.1], component, and system must be specified.

3. The numerical quantity value [VIM 1.20] of purity is often expressed as per cent or per mille.

4. Purity can be estimated as 1−∑j=1j=Nfj, where f_j denotes fractions of the same type (mass fraction, amount of substance fraction or number fraction) of all other components j = 1, …, N. If the contributions are expressed as mass fractions, this estimation is sometimes termed “mass balance”.

3.23 chemical substance

substance

Matter of constant composition best characterized by the entities (molecules, formula units, atoms) it is composed of.

1. Note: Physical quantities [VIM 1.1] such as density, refractive index, electrical conductivity, and melting point characterize a chemical substance.

2. [26] entry C01039 (http://goldbook.iupac.org/terms/view/C01039).

3.24 component

Part of a system.

1. [27].

2. Note 1: A component can consist of different chemical species.

3. Note 2: ‘Part’ is not to be taken for an aliquot or a portion or a sample of a system.

3.25 consensus property value

consensus value

Property value derived from a collection of results.

1. Note 1: The term “consensus value” is typically used to describe estimates of a measure of location, such as mean value, median or mode, and dispersion derived from results reported by participants in a proficiency testing round (see participant in an interlaboratory comparison), but may also be used to refer to values derived from results of a specified subset of such results or, for example, from a number of laboratories chosen for their expertise for the particular analysis. See performance score and standard deviation for proficiency assessment.

2. [28].

3. Note 2: The consensus property value, when it is a value of a unitary quantity, may be expressed as a mean, median, or mode, and is then termed “consensus mean”, “consensus median”, or “consensus mode”, respectively. The mode and the median also apply for ordinal quantities [VIM 1.26] and the mode applies for nominal properties [VIM 1.30].

4. Note 3: A consensus property value is an example of assigned value.

5. Note 4: A consensus property value could, through appropriate actions, become a certified property value; this is in analogy to the certification of a reference material.

6. Note 5: A consensus property value may be obtained in a material-certification study or by agreement between appropriate organizations or experts.

7. Source: [29, 30].

3.26 conventional quantity value

conventional value of a quantity

conventional value

Quantity value [VIM 1.19] attributed by agreement to a quantity [VIM 1.1] for a given purpose.

1. Conventional quantity value of a given mass standard,

   m = 100.003 47 g.

2. Note 2: Sometimes a conventional quantity value is an estimate of a true quantity value [VIM 2.11].

3. Note 3: A conventional quantity value is generally accepted as being associated with a suitably small measurement uncertainty [VIM 2.26], which might be zero.

4. Source: [VIM 2.12] with Note 1 and Examples 1 and 2 omitted.

5. Relative atomic mass for carbon as listed in the IUPAC Green Book [8] p 117.

6. Consensus property value of the measured values [VIM 2.10] of an interlaboratory comparison [28]entry 3.11.

7. Note 4: In quality assurance and quality control in chemistry, a conventional quantity value, which may be a consensus property value, is often termed “assigned value”.

3.27 critical value, L_c

critical level

decision level

Measured quantity value [VIM 2.10] for a quantity [VIM 1.1] of a component in a material, above which the component is declared to be present.

1. Note 1: The critical value is usually considered to be a characteristic of a particular measurement procedure performed in a particular laboratory.

2. Note 2: In some European legislations, the term “decision limit” (denoted as CCα) is used for the concept ‘critical value’ [31].

3. Note 3: The quantity measured is usually a mass fraction or a concentration but can also be, for example, a mass or an amount of substance.

4. Note 4:The critical value is chosen to give a probability α (usually 0.05) of a measured quantity value exceeding the critical value when the component is absent.

5. Note 5: The detection decision is made by comparing a measured quantity value with the critical value.

6. Note 6: Another important concept in characterizing the capability of detection of measurement procedures is the limit of detection.

7. [13, 32].

3.28 determination

Set of operations that are carried out on an object in order to provide qualitative or quantitative information about this object.

1. Note 1: “Determination” is a term in general usage and often implies a human decision.

2. Note 2: ‘Determination’ is a superordinate concept of measurement and examination [12], and so, the term “determination” should not be used when “measurement” or “examination” applies.

3. Note 2: ISO 9000 defines determination as “activity to find out one or more characteristics and their characteristic values” [33].

4. [34]. See also: testing.

3.29 interference

Process whereby a measured quantity value [VIM 2.10] is changed by an influence quantity [VIM 2.52].

Entry replaces recommendation in [35] p 554.

3.30 interferent

Component of the matrix that embodies an influence quantity [VIM 2.52].

1. In the analysis of arsenic using inductively coupled plasma-mass spectrometry at low mass resolution, the presence of chloride in the analytical sample causes the formation of ⁴⁰Ar³⁵Cl⁺ which has the same m/z value of 75 as As⁺.

3.31 intermediate measurement precision

intermediate precision

Measurement precision [VIM 2.15] under intermediate precision conditions of measurement [VIM 2.22].

1. [VIM 2.23].

2. Note: “Intralaboratory precision” or “within-laboratory precision” is sometimes used as a synonym of intermediate measurement precision.

3.32 internal standard

Component used for reference present in or added to a sample to perform calibration [VIM 2.39] or, to assist in identification of a chemical species, or as part of procedure validation.

1. An internal standard provides an indication [VIM 4.1] that varies in the same way as that of the analyte during chemical analysis. The ratio of the indications for analyte and internal standard provides a quantity value [VIM 1.19] that can be used in calibration.

2. In multicomponent mixtures, a component that is known to be in constant concentration or content across samples can be used as an internal standard.

3. An added internal standard may be a spike.

Entry replaces recommendation in [36] p 837.

3.33 laboratory bias

Contribution to measurement bias [VIM 2.18] that is attributed to systematic effects on measurement results [VIM 2.9] made in a laboratory.

1. Measurement bias in analytical chemistry may be considered to include run bias, laboratory bias, and measurement procedure bias.

3.34 laboratory sample

Sample as prepared for sending to a laboratory and intended for inspection or testing.

1. Note: When no preparation of a laboratory sample is required before analysis, the laboratory sample is an analytical sample.

2. [17] Appendix B. See also: primary sample, aliquot, sampling plan, and sample pre-treatment.

3.35 limit of detection (LOD)

detection limit (DL)

True quantity value [VIM 2.11] for a quantity [VIM 1.1] of a component present in a material for which the probability of falsely claiming the absence of the component is β, given a probability α of falsely claiming its presence based on an established criterion for detection.

1. Note 1: The limit of detection is usually considered to be a performance characteristic of a measurement procedure performed in a particular laboratory.

2. Note 2: The quantity is usually a mass fraction or a concentration but can also be, for example, a mass or an amount of substance.

3. Note 3: The established criterion for detection can be, for example, a critical value which leads to a declaration that the component is present.

4. Note 4: IUPAC recommends default values for α and β equal to 0.05. This corresponds to requiring a level of confidence (see coverage probability [VIM 2.37] Note 2) of 95 % for a statistical test for non-zero true value of the quantity and to a statistical power of 95 % for that test applied to a material containing the component at the limit of detection.

5. Note 5: The limit of detection is not a criterion for detection but indicates the true value of a quantity of the component in a material that can be detected reliably, given a separate criterion (for example, critical value) for declaring the component present.

6. Note 6: If the limit of detection is estimated as a multiple of the standard deviation of measured quantity values [VIM 2.10] of a blank material (or one spiked with a small aliquot of the component) measured under repeatability conditions of measurement, it is important to document the multiplication factor applied so that different values stated for limits of detection can be compared.

7. Note 7: The letter symbols LOD and DL should not replace the quantity symbol but may be given as a subscript to the appropriate symbol for the quantity, for example w_LOD, m_DL.

8. Note 8: In ISO 3534-2, ‘minimum detectable value of the net state variable’ is defined as “true value of the net state variable in the actual state that will lead, with probability, 1 − error probability, to the conclusion that the system is not in the basic state” [4].

9. Note 9: According to the definition given here and in ISO 11843, LOD is a (unobservable) true value. This differs from the definition in VIM 4.18, where the concept ‘detection limit’ refers to a measured quantity value [1].

10. Note 10: In some European legislations, ‘detection capability’ (denoted as CCβ) is defined as “the smallest content of the substance that may be detected, identified, and/or quantified in a sample with an error probability of β” [31].

11. Note 11: The ISO 11843 series “Capability of detection” covers a wide field related to “the detection of a difference between an actual state of a system and its basic state”, which additionally includes cases in which the ‘basic state’ does not correspond to the absence (zero concentration) of a component [37].

12. Note 12: The use of the term “sensitivity” for limit of detection is erroneous as it refers to the slope of the calibration curve.

13. Note 13: The US Environmental Protection Agency defines ‘method detection limit’ (MDL) as “the minimum measured concentration of a substance that can be reported with 99 % confidence that the measured concentration is distinguishable from method blank results” [38].

14. [9, 13, 32, 39]. Entry replaces recommendation in [9] p 5.

3.36 limit of quantification (LOQ)

quantification limit

Smallest or largest measured quantity value [VIM 2.10], obtained by a given measurement procedure, which fulfils a requirement of fitness for purpose.

1. Note 1: The quantity [VIM 1.1] measured is usually a mass fraction or a concentration but can also be for example, a mass or an amount of substance.

2. Note 2: The requirement can, for example, be a standard deviation under repeatability conditions of measurement or a measurement uncertainty [VIM 2.26].

3. Note 3: The smallest and largest measured quantity values correspond to the lower limit of quantification (LLOQ) and the upper limit of quantification (ULOQ), respectively. The interval between the LLOQ and ULOQ is the working interval.

4. Note 4: If the LLOQ is estimated as a multiple of the standard deviation of measured values of a blank material (or one spiked with a small aliquot of the component) obtained under repeatability conditions of measurement, it is important to document the multiplication factor, which may be 5, 6, or 10, applied so that different values stated for the LLOQ can be compared.

5. [32, 40].

3.37 linearity of a measuring system

Ability of a measuring system [VIM 3.2] to provide measured quantity values [VIM 2.10] that are directly proportional to the quantity value [VIM 1.19] of the measurand.

1. [41]. See also: [42].

2. Note 1: The linearity of a measuring system is assessed during procedure validation.

3. Note 2: The set of measured quantity values for which linearity of a measuring system applies is usually termed “linear interval” or “linear range”.

4. Note 3: Linearity of a measuring system should not be confused with linearity of calibration.

3.38 linearity of calibration

calibration linearity

Closeness of agreement between indications [VIM 4.1] obtained using calibrators [VIM 5.12] in the first step of a calibration [VIM 2.39] and indications predicted by the calibration function for the calibrators’ reference quantity values [VIM 5.18].

1. The concept applies to calibration functions of any mathematical form. The term ‘linearity’ is historical and refers to a time when calibration graphs were constructed on paper and were invariably considered to be linear.

2. Linearity of calibration may be expressed by measures of agreement (for example, correlation coefficient) or deviation (for example, standard error of regression), obtained by regression of calibration data or assessed from a residual plot. See also: [43].

3. Linearity of calibration is assessed during procedure validation.

4. Calibration linearity should not be confused with linearity of a measuring system.

5. See also: [20].

3.39 lot

Material which is assumed to be uniform for the purpose of sampling.

1. Note: Some vocabularies assume “lot” and “batch” to be synonymous. The distinction made here with respect to the knowledge of production history permits a lot to consist of one or more batches and is useful in interpreting the results of chemical analysis. See also definitions in ISO 11961 [44], ISO 472 [45], ISO 15736 [46], and ISO 18113-1 [47].

Entry replaces recommendation in [18] entry 2.2.2.

3.40 mass balance

See: chemical purity.

3.41 material homogeneity

homogeneity

Uniform structure or composition of a material with respect to one or more specified properties.

1. Note 1: A material is said to be homogeneous with respect to a specified quantity [VIM 1.1] if the quantity values [VIM 1.19] measured using aliquots of a specified size do not fall outside a specified interval. See minimum sample size.

2. In the homogeneity study of a candidate reference material, it is distinguished whether the analytical samples are taken from different supply units or from a single supply unit (“termed between-bottle homogeneity” or “within-bottle homogeneity”, respectively) [2].

3. Inhomogeneity is a source of measurement uncertainty [VIM 2.26].

4. Detailed guidance for the assessment of homogeneity of reference materials [VIM 5.13] is given in ISO Guide 35 [48].

Entry replaces recommendation in [18] p 1201.

3.42 material recovery

recovery

Mass (volume, amount of substance) of a specified component isolated from a system divided by the mass (volume, amount of substance) of the system prior to isolation.

1. [49].

2. Note 1: The measurement unit [VIM 1.9] of material recovery is the measurement unit of the quantity [VIM 1.1] related to the specified component divided by the unit of the quantity describing the system. When these units are the same, material recovery may be expressed as a percentage, and the quantity specified.

3. Note 2: The term “recovery” is also used to describe a recovered quantity value ratio. Therefore, the term “recovery” should not be used without qualification unless the meaning is clear from the context.

See also: [50].

3.43 material stability

stability

Constancy of a property of a material over time.

1. Note 1: A material is said to be stable with respect to a specified property if its measured or examined property value does not fall outside a specified interval during storage under specified conditions over a specified period of time.

2. Note 2: A reference material is assessed for the stability of an embodied property under conditions of transport (‘short-term stability’) and storage (‘long-term stability’).

3. [2].

4. Note 3: The variation of the property value over time adds a contribution to the uncertainty budget [VIM 2.33] or the examination uncertainty [12], as applicable. Regarding the assessment of stability of the reference material, detailed guidance is given in ISO Guide 35 [48].

5. Note 4: The term ‘stability’ is also used for stability of a measuring instrument [VIM 4.19] or process (see control limit).

3.44 matrix

Analytical sample excluding the analyte.

1. In matrix reference material, the concept ‘matrix’ is used in the sense of a kind of material.

See also: blank material Note 2. Entry replaces recommendation in [19] p 1660.

3.45 matrix effect

Systematic measurement error [VIM 2.17] caused by the matrix.

See also: multiplicative matrix effect and additive matrix effect. Entry replaces recommendation in [26] definition 1.

3.46 measurand

Quantity [VIM 1.1] intended to be measured.

1. Note 1: The specification of a measurand requires knowledge of the kind of quantity [VIM 1.2], description of the state of the phenomenon, body, or substance embodying the quantity, including any relevant component, and the chemical entities involved.

2. Note 3: The measurement, including the measuring system [VIM 3.2] and the conditions under which the measurement is carried out, might change the phenomenon, body, or substance such that the quantity being measured may differ from the measurand as defined. In this case, adequate correction [VIM 2.53] is necessary.

3. The length of a steel rod in equilibrium with an ambient Celsius temperature of 23 °C will be different from the length at the specified temperature of 20 °C, which is the measurand. In this case, a correction is necessary.

4. Note 4: In chemistry, “analyte”, or the name of a substance or compound, is the term sometimes used for ‘measurand’. This usage is erroneous because these terms do not refer to quantities.

5. The electric potential difference between the terminals of a battery decreases when using a voltmeter with a significant internal conductance to perform the measurement. The open-circuit potential difference can be calculated from the internal resistances of the battery and the voltmeter.

6. Source: [VIM 2.3] with Note 2 and Example 1 omitted.

7. Note 5: The measurand may be operationally defined by reference to a documented measurement procedure to which only quantity values [VIM 1.19] obtained by the same procedure can be compared.

8. Source: [51]. Entry replaces recommendation in [52] p 980.

3.47 measurement

Process of experimentally obtaining one or more quantity values [VIM 1.19] that can reasonably be attributed to a quantity [VIM 1.1].

1. Note 1: Measurement does not apply to nominal properties [VIM 1.30].

2. Note 2: Measurement implies comparison of quantities or counting of entities.

3. Note 3: Measurement presupposes a description of the quantity commensurate with the intended use of a measurement result [VIM 2.9], a measurement procedure, and a calibrated measuring system [VIM 3.2] operating according to the specified measurement procedure, including the measurement conditions.

4. [VIM 2.1].

5. Note 4: Measurement is a subordinate concept of determination, and so, the term “determination” should not be used when “measurement” applies.

6. Note 5:  If a measurement result is assessed with respect to conditions implied by a norm, standard, or specified requirement (that is, in conformity assessment), measurement is often termed testing.

Entry replaces recommendation in [53] p 1565.

3.48 measurement procedure

Detailed description of a measurement according to one or more measurement principles [VIM 2.4] and to a given measurement method [VIM 2.5], based on a measurement model [VIM 2.48] and including any calculation to obtain a measurement result [VIM 2.9].

1. Note 1:A measurement procedure is usually documented in sufficient detail to enable an operator to perform a measurement.

2. Note 2:A measurement procedure can include a statement concerning a target measurement uncertainty.

3. [VIM 2.6] with Note 3 omitted.

4. Note 4:Measurement procedures in chemistry can be structured according to ISO 78-2 [54] or Annex A of the Eurachem Guide “The Fitness for Purpose of Analytical Methods” [20].

5. Note 5:An authorized measurement procedure is sometimes termed “standard operating procedure” (SOP) or “recommended operating procedure” (ROP).

6. Note 6:In ISO/IEC 17025 [23], the term “method” is used for measurement procedure. “Examination procedure” is defined for medical laboratories [7, 55].

7. Note 7:The historical term “assay” is now largely obsolete as a synonym for metrological terms such as measurement procedure but still used in composite terms, for example, immunoassay and bioassay.

3.49 measurement procedure bias

measurement method bias

Contribution to measurement bias [VIM 2.18] that is attributed to systematic effects on measurement results [VIM 2.9] made according to a measurement procedure.

1. Measurement procedure bias covers instrumental bias [VIM 4.20].

2. Contributions to measurement procedure bias are calculated during procedure validation [20].

3. Measurement bias in analytical chemistry may be considered to include run bias, laboratory bias, and measurement procedure bias [56].

3.50 measurement procedure with standard addition

standard addition

Measurement procedure in which indications [VIM 4.1] are obtained for an analytical sample as well as for analytical samples with addition(s) of a measurement standard [VIM 5.1].

1. Note: A measurement procedure with standard addition provides an unbiased measurement result [VIM 2.9] if there is a multiplicative matrix effect.

2. [14].

3.51 measurement reproducibility

reproducibility

Measurement precision [VIM 2.15] under reproducibility conditions of measurement [VIM 2.24].

1. Note 1: Relevant statistical terms are given in ISO 5725-1 [57] and ISO 5725-2 [58].

2. [VIM 2.25].

3. Note 2: The term “interlaboratory precision” or “between-laboratory precision” is sometimes used as a synonym of measurement reproducibility.

3.52 measuring interval

See: working interval.

3.53 metrological compatibility of measurement results

metrological compatibility

Property of a set of measurement results [VIM 2.9] for a specified measurand, such that the absolute value of the difference of any pair of measured quantity values [VIM 2.10] from two different measurement results is smaller than some chosen multiple of the standard measurement uncertainty [VIM 2.30] of that difference.

1. Note 1: Metrological compatibility of measurement results replaces the traditional concept of ‘staying within the error’, as it represents the criterion for deciding whether two measurement results refer to the same measurand or not. If in a set of measurements of a measurand, thought to be constant, a measurement result is not compatible with the others, either the measurement was not correct (for example, its measurement uncertainty [VIM 2.26], was assessed as being too small), or the measured quantity [VIM 1.1] changed between measurements.

2. Note 2: Correlation between the measurements influences metrological compatibility of measurement results. If the measurements are completely uncorrelated, the standard measurement uncertainty of their difference is equal to the root square sum of their standard measurement uncertainties, while it is lower for positive covariance or higher for negative covariance.

3. [VIM 2.47] with corrected Note 2.

4. Note 3: As required by the Mutual Recognition Arrangement (MRA) of the International Committee for Weights and Measures (CIPM), through which national metrology institutes demonstrate the international equivalence of their measurement standards [VIM 5.1], the concept ‘degree of equivalence’ is applied in special interlaboratory comparisons termed “key comparisons”. The degree of equivalence of each national measurement standard [VIM 5.3] is expressed quantitatively by two terms: its deviation from the reference quantity value [VIM 5.18] of the key comparison and the measurement uncertainty of this deviation (at a level of confidence of approximately 95 %). See also: metrological equivalence of measurement results.

5. [59].

3.54 metrological equivalence of measurement results

equivalence of measurement results

Property of two or more measurement results [VIM 2.9] for a given measurand which have metrologicalcompatibility of measurement results, so that they are each acceptable for the same specified intended use.

1. Note: Measurement results are either metrologically equivalent or they are not.

2. [60].

3.55 minimum sample size

minimum sample intake

Lower limit of sample size stipulated in documentation taken for chemical analysis.

1. Note 1: Examples of documentation include a measurement procedure, product information sheets (see reference material), and reference material certificates.

2. Note 2: Values associated with performance characteristics of a measurement procedure and the property values stated in documentation are rendered invalid if the minimum sample size is not taken.

3. Adapted from [2] entry 2.1.8.

3.56 multiplicative matrix effect

Matrix effect that is proportional to the measured quantity value [VIM 2.10] of the measurand.

1. A multiplicative matrix effect can be compensated for by following a measurement procedure with standard addition.

2. A multiplicative matrix effect affects the slope, not the intercept, of a linear calibration curve.

3. The effect is sometimes termed “rotational matrix effect” or “proportional interference” [14].

4. A multiplicative matrix effect may originate from non-analyte components of the measurement standard [VIM 5.1] if these contribute to the signal attributed to the analyte.

3.57 non-certified property value

Property value that is provided for information only but is not certified by a reference material producer.

1. Note 1: A non-certified property value cannot be used as reference in a metrological traceability chain [VIM 2.42].

2. Note 2: A non-certified property value may be included in the reference material certificate or supplied in other form.

3. Note 3: In ISO Guide 30 [2], “indicative value”, “information value”, and “informative value” are admitted terms.

4. [2, 61].

3.58 object traceability

traceability

deprecated: trackability

Ability to trace the history, application, or location of an object.

1. Note 1: When considering a product or a service, traceability can relate to: the origin of materials and parts, the processing history, or the distribution and location of the product or service after delivery.

2. Note 2: In [62], the term defined is “traceability”. However, because of the potential confusion with metrological traceability [VIM 2.41], it is recommended to use the full term if there is ambiguity.

3. [62].

3.59 primary sample

Collection of one or more sampling increments initially taken from material intended to be analysed.

1. [18].

2. Note: The term primary, in this case, does not refer to the quality of the sample, rather the fact that the sample was taken during the earliest stage of measurement.

See also: [17] Appendix B.

3.60 property value assignment

value assignment

Determination of property values obtained in the course of the production of a reference material.

See also: [2], assigned value.

3.61 recovered quantity value ratio, R

analytical recovery

recovery

Measured quantity value [VIM 2.10] relating a component to a system divided by a reference value [VIM 5.18].

1. Note 1:The quantities [VIM 1.1] involved are rational unitary quantities and of the same kind of quantity [VIM 1.2], usually either a concentration or content.

2. Note 2:The respective measurement procedure must be specified.

3. Note 3:The definition can be symbolized by RB=QB,measured/QB,reference, where R denotes the recovered ratio of the quantity values [VIM 1.19] Q, and B identifies the component.

4. Note 3:The term “recovery” is also used to describe material recovery. Therefore, the term “recovery” should not be used without qualification unless the meaning is clear from the context.

5. Note 5:Recovery quantity value ratio is used in procedure validation to evaluate and correct for the measurement procedure bias [20].

6. Note 6:Recovered quantity value ratio may be estimated from the measured change of the quantity value of the component of interest upon the addition of a known amount of substance or mass of the component. The added material containing the component is often termed “spike”. See also: blank material Note 5, measurement procedure with standard addition, and spike.

7. [20, 50]. Entry replaces recommendation in [26] definition 2.

3.62 repeatability condition of measurement

repeatability condition

Condition of measurement, out of a set of conditions that includes the same measurement procedure, same operators, same measuring system [VIM 3.2], same operating conditions, and same location, and replicate measurements on the same or similar objects over a short period of time.

1. Note 1: A condition of measurement is a repeatability condition only with respect to a specified set of repeatability conditions.

2. [VIM 2.20] with Note 2 omitted.

3. Note 3: In ISO 3534-2, “same operator” (singular) is stipulated as a repeatability condition. The VIM request of “same operators” (plural) should be understood such that if two or more operators contribute to one measurement, they should be involved in the same way in repeated measurements [4].

4. Note 4: In analytical chemistry, the phrase “under repeatability conditions” refers to the above specified set of conditions.

5. Note 5: A set of measurements under repeatability conditions is often termed “analytical run”.

3.63 replicate (duplicate) samples

Multiple (two) samples taken under compatible conditions.

1. Note 1:This selection may be accomplished by taking sampling increments adjacent in time or space. Although the replicate samples are expected to be identical, often the only thing replicated is the act of taking the physical sample.

2. [18] p 1203.

3. Note 2:In ISO 3534-2, ‘replicate sampling’ is defined [4] entry 5.2.5.

3.64 run bias

Contribution to measurement bias [VIM 2.18] that is attributed to systematic effects on measurement results [VIM 2.9] made in a single analytical run.

1. Measurement bias in analytical chemistry may be considered to include run bias, laboratory bias, and measurement procedure bias.

3.65 sample

Portion of a material taken for qualitative analysis or quantitative analysis.

1. Note 1:Taking a sample from a material implies the existence of a sampling error [17], that is, the measured quantity values [VIM 2.10] of the portion’s properties are only estimates of those of the parent material.

2. Note 2:If the portion is removed with negligible sampling error, it is termed an aliquot or specimen. ‘Specimen’ is used to denote a portion taken under conditions such that the sampling variability cannot be assessed and is assumed, for convenience, to be zero.

3. Note 3:The sampling plan should detail how a sample is obtained and any subsequent manipulations (see sample pre-treatment).

4. Note 4:Fundamentals of sampling and sample pre-treatment in analytical chemistry are detailed in [63, 64].

5. In analytical chemistry, ‘sample’ must not be confused with a subset of a population for which the term “sample” is used in statistics.

6. [9]. See also: analytical sample, primary sample, replicate sample, and spike. Entry replaces recommendation in [26] entry S05451 (https://doi.org/10.1351/goldbook.S05451).

3.66 sample pre-treatment

sample preparation

Collective noun for all procedures used for conditioning a sample to a defined state which allows subsequent chemical analysis or long-term storage (see material stability).

1. Note: Sample pre-treatment includes, for example, mixing, splitting, drying, crushing, stabilization, dissolving, extracting, diluting, precipitating, and derivatizing.

2. [17] Appendix B.

3.67 sampling

Act of taking or constituting a sample.

1. Note: Sampling often provides a contribution to the measurement uncertainty budget [VIM 2.33] or the examination uncertainty [12], as applicable. See: [17].

2. [4].

3.68 sampling increment

increment

Individual portion of material collected by a single operation of a sampling device.

1. [17] Appendix B. See also: primary sample.

3.69 sampling plan

Predetermined procedure for the selection, withdrawal, preservation, transportation, and preparation (see sample pre-treatment) of the portions to be removed from a material as a sample.

1. [17] Appendix B. Entry replaces recommendation in [18] p 1201.

3.70 sampling target

Portion of material, at a particular time, that the sample is intended to represent.

1. Note 1: The sampling target should be defined prior to designing the sampling plan.

2. Note 2: The sampling target may be defined by Regulations (for example, lot size).

3. [17] Appendix B.

3.71 shelf life

Time interval during which a reference material producer warrants the material stability of the reference material.

1. Note: The shelf life is equivalent to the ‘period of validity’ of the reference material certificate and is ended by the ‘expiry date’.

2. [48].

3.72 spike

Material with known quantity values [VIM 1.19] added to an analytical sample.

1. The material can be a reference material or a certified reference material [VIM 5.14].

2. The known quantity value is often a fraction or concentration.

3. A spike may be used to estimate the recovered quantity value ratio or compensate for systematic measurement error [VIM 2.17].

4. “Spike” used as a verb is the addition of a spike to a sample.

3.73 system

Part or phenomenon of the perceivable or conceivable universe consisting of a demarcated arrangement of a set of entities and a set of relations between these entities.

1. Source: [27].

2. Note: The concept covers both immaterial systems such as the International System of Units (SI) [VIM 1.16] and material systems such as a measuring system [VIM 3.2]. In laboratory medicine, the term “system” usually denotes a composite object [7] such as a living organism or tissue; in analytical chemistry, the term is used to emphasize complex interaction of components.

3. The tailings dam of a mine containing water and suspended solids, heavy metals, and other chemical substances, at a particular time, subject to investigation by an environmental protection agency.

4. Residue from a flask suspected to contain illegal drugs seized by the police and submitted for forensic examination.

3.74 systematic effect

Recognized effect of an influence quantity [VIM 2.52] on a measured quantity value [VIM 2.10].

1. A systematic effect can be compensated for by a correction [VIM 2.53].

3.75 testing

test

Determination of one or more characteristics of an object of conformity assessment, according to a specified procedure.

1. [65]. See also: inspection.

2. Note: In analytical chemistry, testing may be a measurement to obtain a quantity value [VIM 1.19] or an examination [12], such as identifying a chemical substance (see qualitative analysis).

3.76 unitary quantity

Quantity [VIM 1.1] with a magnitude expressed as a reference quantity multiplied by a number.

1. In the VIM [1], the concept is denoted as “quantity expressed by a measurement unit” in the concept diagram Figure A.1 and is referred to as “quantities other than ordinal quantities”, for example, in entry 1.21, and as “non-ordinal quantity” in Note 1 to entry 2.41.

2. Source: [66]. See also: [27].

3.77 working interval

working range

Set of quantity values [VIM 1.19] over which a measuring instrument [VIM 3.1] or measuring system [VIM 3.2] provides measurement results [VIM 2.9] with acceptable measurement uncertainty [VIM 2.26] under defined conditions.

1. Note 1: In some fields, the term is “measurement range”. In entry 4.7 of VIM [1], a similar concept termed “measuring interval” is defined.

2. Note 2: The working interval is bounded by the lower and upper limit of quantification.

3. Note 3: The lower limit of a working interval should not be confused with the detection limit.

4. [20] section 6.3. See also: linearity of a measuring system Note 2.

4.78 acceptance interval

acceptance zone

Interval of permissible measured quantity values [VIM 2.10].

1. Note 1: Unless otherwise stated in the specification, the acceptance limits belong to the acceptance interval.

2. Note 2: An acceptance interval is termed an ‘acceptance zone’ in the Eurachem guide on compliance assessment [69].

3. [70] entry 3.3.9. See also: decision rule in conformity assessment, rejection interval.

4.79 acceptance limit

Specified upper or lower bound of permissible measured quantity values [VIM 2.10].

1. [70] entry 3.3.8.

2. Note: Permissible measured quantity values are associated with items that conform to specified requirements with at least a predetermined conformance probability and lie within the acceptance interval.

See also: conformity assessment.

4.80 accreditation of a laboratory

Third-party attestation related to a laboratory conveying formal demonstration of its competence to carry out specific conformity assessment tasks.

1. Accreditation of an analytical chemistry laboratory to ISO/IEC 17025 [23] for the measurement of the mass concentration of lead in environmental samples.

2. Note 1: Examples of conformity assessment tasks for which accreditation can be granted are measurement, testing, inspection, provision of proficiency testing schemes, and production of reference materials.

3. Note 2: The criteria for determining a laboratory’s competence are based on relevant international standards, for example, ISO/IEC 17025 [23], ISO 15189 [55], or ISO 15195 [71], and include adequate quality assurance and quality control procedures, such as qualifications, training and experience of staff, appropriate equipment that is properly calibrated and maintained, use of validated measurement procedures, participation in interlaboratory comparisons, and appropriate sampling practices.

4. Source: [65].

4.81 analytical selectivity

selectivity

Selectivity of a measuring system [VIM 4.13] in analytical chemistry.

1. Selectivity should be qualified by ‘analytical’ if there is potential confusion with selectivity in catalysis or in organic reaction mechanisms.

See also: [20, 72]. Entry replaces recommendation in [35] p 555.

4.82 assessor

Person, assigned by an accreditation body, with relevant professional expertise and experience who can determine the competence of a laboratory.

1. Note 1: The assessor may work alone or as part of a team and be engaged in a voluntary or paid capacity.

2. Note 2: The work of an assessor is often referred to as “assessment” and sometimes as “peer review”.

3. Note 2: Depending on the role and responsibilities of an assessor, terms such as “lead assessor” and “technical assessor” are often used.

4. adapted from [73] entry 3.30.

4.83 assigned value

Value attributed to a particular property of an item and that serves as an agreed reference for comparison.

1. Note 1: The value may be a reference quantity value [VIM 5.18] or a value of a nominal property [VIM 1.30].

2. Note 2: Options for establishing an assigned value for some types of proficiency testing schemes are detailed in ISO/IEC 17043 [30] and ISO 13528 [28].

3. [74] entry 2.7, [30]. See also: property value assignment.

4.84 audit

Systematic, independent, and documented process for obtaining objective evidence and evaluating it objectively to determine the extent to which the audit criteria are fulfilled.

1. Note 1: The fundamental elements of an audit include the determination of the conformity of an object according to a procedure carried out by personnel not being responsible for the object audited.

2. Note 2: An audit can be an internal audit (first party) or an external audit (second party or third party), and it can be a combined audit or a joint audit.

3. Note 3: Internal audits, sometimes termed first-party audits, are conducted by, or on behalf of, the organization itself for management review and other internal purposes and can form the basis for an organization’s declaration of conformity. Independence can be demonstrated by the freedom from responsibility for the activity being audited.

4. Note 4: External audits include those generally termed second and third-party audits. Second-party audits are conducted by parties having an interest in the organization, such as customers, or by other persons on their behalf. Third-party audits are conducted by external, independent auditing organizations such as those providing certification/registration of conformity or governmental agencies.

5. [62] entry 3.13.1.

4.85 candidate certified reference material

candidate CRM

Reference material subjected to a process of reference material certification.

4.86 candidate reference material

candidate RM

Material subjected to the procedures necessary to show its fitness for intended use (see fitness for purpose).

1. Note: A candidate reference material for a given property may already be a reference material for other properties.

2. [2].

4.87 capability

Ability of an object to realize an output that will fulfil the requirements for that output.

1. Note: Process capability terms in the field of statistics are defined in ISO 3534-2 [4].

2. [62].

4.88 cause-and-effect diagram

Ishikawa diagram

herringbone diagram

fishbone diagram

Diagram indicating the causes of a specific event or condition.

1. Note: In analytical chemistry, Ishikawa diagrams are used to indicate sources of measurement uncertainty [VIM 2.26]. See Fig. 4.88-1.

2. [75].

Fig. 4.88-1:

Ishikawa diagram for the titration of a hydrochloric acid solution with sodium hydroxide solution that has been standardized using potassium hydrogen phthalate (KHP). When used for identification of sources of measurement uncertainty, the diagram illustrates how the quantity value [VIM 1.19] of the measurand (c_HCl) depends on input quantities in a measurement model [VIM 2.50] (symbols in bold), which in turn depend on other quantities [VIM 1.1]. Symbols have their usual meanings. f_precision is a is a factor in the measurement function [VIM 2.49] to account for measurement precision [VIM 2.15] with value 1 and standard measurement uncertainty [VIM 2.30] (see [75] Fig. A3.5).

4.89 certification

Third-party attestation related to products, processes, systems, or persons.

1. Note 1: Certification of a management system is sometimes also termed registration.

2. Note 2: Certification is applicable to all objects of conformity assessment except for conformity assessment bodies themselves, to which accreditation is applicable.

3. [65].

4.90 commutability of a reference material

Property of a reference material, demonstrated by the closeness of agreement between the relation among the measurement results [VIM 2.9] for a stated quantity [VIM 1.1] in this material, obtained according to two given measurement procedures, and the relation obtained among the measurement results for other specified materials.

1. Note 1: The reference material in question is usually a calibrator and the other specified materials are usually routine samples.

2. Note 2: The measurement procedures referred to in the definition are the one preceding and the one following the reference material (calibrator) in question in a calibration hierarchy [VIM 2.40] (see ISO 17511 [76]).

3. Note 3: The material stability of commutable reference materials should be monitored regularly.

4. [VIM 5.15].

5. Note 4: Cases in which a reference material producer is required to conduct assessment of commutability are outlined in ISO 15194 [77].

6. Note 5: Guidance for assessment of commutability of reference material in laboratory medicine is provided by IFCC [78], [79], [80].

4.91 competence

Ability to apply knowledge and skills to achieve intended results.

1. Note: Demonstrated competence is sometimes referred to as “qualification”.

2. [62].

4.92 conformance probability

Probability that an item fulfils a specified requirement.

1. [70].

4.93 conformity assessment

compliance assessment

Activity to determine whether specified requirements relating to a product, process, system, person, or body are fulfilled.

1. Note 1: The subject field of conformity assessment includes activities, such as testing, calibration [VIM 2.39], carrying out an audit, inspection, and certification, as well as the accreditation of conformity assessment bodies.

2. Note 2: The expression “object of conformity assessment” or “object” is used to encompass any particular material, product, installation, process, system, person, or body to which conformity assessment is applied.

3. [65] entry 3.3.1.

4. Note 3: “Body” refers to an organization.

See also: tolerance interval, acceptance interval, rejection interval, decision rule, guard band, and Figs. 4.102-1 and 4.102-2.

Fig. 4.102-1:

Guarded acceptance. Two-sided acceptance interval created by reducing the tolerance interval on either side by a guard band, thus reducing the probability of falsely accepting a non-conforming item.

Fig. 4.102-2:

Guarded rejection. Two-sided acceptance interval created by increasing the tolerance interval on either side by a guard band, thus reducing the probability of falsely rejecting a conforming item.

4.94 control chart

Chart with control limits on which some statistical measure related to a series of samples is plotted in a particular order to steer the process with respect to that measure.

1. Note 1: The particular order is usually based on time or sample number order. Repeated sampling may be avoided where in-situ measurements are applicable.

2. Note 2: The control chart operates most effectively when the measure is a process variable which is correlated with an ultimate product or service characteristic.

3. [4] entry 2.3.1.

4. Note 3: Examples of control charts are Shewhart means chart, Shewhart range chart, and cumulative sum control chart.

5. Note 4: Control charts are commonly used in the regular monitoring of the performance of a measurement procedure, as part of the laboratory’s internal quality control.

4.95 control limit

Value defining an intended level of stability for a process.

1. [81].

2. Note 1:A control limit may be a statistical value or be related to a predetermined target value, calculated, for example, from a target measurement uncertainty. See [82].

3. Note 2:A typical control chart will consist of a centre line that reflects the level around which the plotted value can be expected to vary. In addition, this control chart will have two lines, called control limits, placed one on each side of the centre line, which define a band within which the value can be expected to lie randomly for a process in a state of statistical control.

4. Note 3:Control limits on a Shewhart control chart are placed at a distance of ±2σ and ±3σ where σ is the known or estimated standard deviation of the population [83]. This gives approximate probabilities of 0.05 and 0.003, respectively, of finding values outside the control limits. These limits are known as the upper and lower warning limit (UWL and LWL) and upper and lower action limit (UAL and LAL), respectively. See Fig. 4.159-1.

5. Note 4:A typical response to a value outside a warning limit is to monitor the process and, if this condition is repeated, to stop and investigate.

6. Note 5: A value outside an action limit is normally taken as evidence that the process is no longer in statistical control. A typical response to such a value is to stop and investigate. (See process in a state of statistical control).

4.96 coordinator of an interlaboratory comparison

coordinator

Person(s) with responsibility for organizing and managing all of the activities involved in the operation of an interlaboratory comparison.

1. [30].

4.97 cumulative sum control chart (CUSUM chart)

Control chart where the cumulative sum of deviations of successive measured quantity values [VIM 2.10] from a reference quantity value [VIM 5.18] is plotted to detect shifts in the level of the measurand.

1. Note 1: The ordinate of each plotted point represents the algebraic sum of the previous ordinate and the most recent deviation from the reference, target, or control value.

2. Note 2: The best discrimination of changes in the level is achieved when the reference quantity value is equal to the overall mean value.

3. Note 3: The chart can be used for control, diagnostic, or predictive purposes.

4. Note 4: When used for process control, it can be interpreted graphically using a mask (for example, V-mask) superimposed on the graph. An out-of-control criterion is when the path of the cumulative sum intersects or touches the boundary of the mask.

5. [4].

6. Note 5: More suited to spreadsheet analysis, the following quantities [VIM 1.1] are calculated for N measured quantity values x_i (i = 1; …, N) Shi(i)=max(0,Shi(i−1)+xi−μ−k); Shi(0)=0Slo(i)=max(0,Slo(i−1)−xi+μ−k); Slo(0)=0

   . μ is a suitably chosen target value and k is a reference quantity value such that only shifts away from the target value greater than k will add to the cumulative sum. k is usually taken as half the shift in the process mean that is required to be detected divided by the standard deviation (σ) obtained under repeatability conditions of measurement. An out-of-control criterion is when Shi(i) or Slo(i) becomes greater than a limiting value h (usually h = 4σ). (Note that the reference quantity value k is not a coverage factor [VIM 2.38]).

7. Note 6: CUSUM charts are particularly sensitive to reveal a small measurement bias [VIM 2.18].

4.98 decision rule in conformity assessment

decision rule

Documented rule that describes how measurement uncertainty [VIM 2.26] will be accounted for with regard to accepting or rejecting an item, given a specified requirement and a measured quantity value [VIM 2.10].

1. [70]. See also: conformity assessment.

2. Note 1:Decision rules in conformity assessment give a prescription for the acceptance or rejection of an item based on the measured quantity value and the associated measurement uncertainty and limit(s) expressed or implied by specified requirements, taking into account the acceptable level of the probability of making a wrong decision. On the basis of the decision rules, an ‘acceptance interval’ and ‘rejection interval(s)’ are determined, such that if the measured quantity value lies in the acceptance interval, the item is declared as conforming and if in the rejection interval, it is declared as non-conforming.

3. [69]. See guard band.

4.99 fitness for purpose

fitness for intended use

Ability of a product, process, or service to serve a defined purpose under specific conditions.

1. [67].

4.100 good laboratory practice (GLP)

Quality system concerned with the organizational process, and conditions under which non-clinical health and environmental safety studies are planned, performed, monitored, recorded, archived, and reported.

1. Note 1: GLP is generally associated with the guidelines laid down by the Organization for Economic Co-operation and Development (OECD). The use of the term GLP outside these guidelines is not recommended.

2. Note 2: A GLP approval should not be confused with accreditation of a laboratory.

3. [84].

4.101 good manufacturing practice (GMP)

Combination of manufacturing and quality procedures aimed at ensuring that products are consistently manufactured to their specified requirements and to avoid contamination of the product by internal or external sources.

1. [85]. See also: [86].

4.102 guard band

Interval between a tolerance limit and a corresponding acceptance limit.

1. [70] entry 3.3.11.

2. Note 1:A guard band is used to restrict or to extend an acceptance interval to reduce the probability of an unwanted decision on conformance due to the measurement uncertainty [VIM 2.26] of the actual measurement. The width of a guard band is scaled with the measurement uncertainty. (See: decision rule in conformity assessment).

3. Note 2:If the acceptance limits lie within the tolerance limits, the decision for conformity of the item is known as guarded acceptance. The probability of falsely accepting a non-conforming item is reduced. This is most often found in chemistry. See Fig. 4.102-1.

4. Note 3:If the acceptance limits lie outside the tolerance limits, the decision for conformity of the item is known as guarded rejection. The probability of falsely rejecting a conforming item is reduced. See Fig. 4.102-2.

See also conformity assessment.

4.103 Horwitz equation

Horwitz trumpet curve

Horwitz horn curve

Horwitz curve

Empirical relationship providing a standard deviation under reproducibility conditions of measurement [VIM 2.24] (sR,H) to be expected for typical measurements of the mass fraction (w) of a component in a material: sR,H=0.02w0.8495.

1. Note:The shape of the curve is called a trumpet [87] when the relative standard deviation is plotted against the logarithm of the mass fraction as shown in Fig. 4.103-1. The reference justifies the mirror curve for negative ordinate values by “… the lines are best regarded as confidence boundaries.”

2. [87].

Fig. 4.103-1:

Horwitz curve (trumpet, horn). Expected relative standard deviation under reproducibility conditions of measurement, ±sR,H/w plotted against logarithm of mass fraction, w.

4.104 Horwitz ratio (Horrat, HorRat, HORRAT), H

Standard deviation of a mass fraction of a component under reproducibility conditions of measurement [VIM 2.24] divided by the corresponding standard deviation calculated from the Horwitz equation.

1. Note 1: The Horwitz ratio is used as a test of the fitness for purpose of methods of chemical analysis.

2. Note 2: The experimental measurement precision [VIM 2.15] is better than to be expected from the Horwitz equation if the Horwitz ratio is less than 1 and poorer if greater than 1. In practice, ratios between 0.5 and 2.0 are acceptable.

3. Note 3: In [88], the “Horwitz ratio” is defined as the ratio of the standard deviation under reproducibility conditions of measurement and standard deviation under repeatability conditions of measurement. This use is discouraged because of the possibility of confusion with the older usage.

4. [89].

4.105 in-house reference material

laboratory reference material

Reference material produced and used by an analytical laboratory.

1. The preparation, characterization, and use of in-house reference materials for quality control purposes are described in ISO Guide 80 [90].

2. Various terms are used to distinguish among reference materials intended for different uses and with assigned values established applying different procedures.

See also: conventional quantity value and property value assignment.

4.106 inspection

Examination of a product, process, service, or installation or their design and determination of conformity with specific requirements or on the basis of professional judgment, with general requirements.

1. Note 1: Inspection of processes can include personnel, facilities, technology, or methodology.

2. Note 2: Inspection procedures or schemes can restrict inspection to examination only.

3. Note 3: If the result of an inspection shows conformity, it can be used for purposes of verification.

4. [62, 91].

5. Note 4: The result of an inspection can show conformity or non-conformity or a degree of conformity, where conformity is defined as fulfilment of a requirement.

4.107 interlaboratory comparison (ILC)

Organization, performance, and evaluation of measurements or tests on the same or similar items by two or more laboratories in accordance with predetermined conditions.

1. Source: [30] entry 3.4.

2. Note 1:Interlaboratory comparison is a generic term, and the purpose and detailed objectives of an interlaboratory comparison must be specified. Some types of interlaboratory comparisons have special names, for example, proficiency testing scheme and key comparison [92].

3. Note 2:Interlaboratory comparisons are organized at all metrological levels and have the following steps in common. a) A coordinator of an interlaboratory comparison plans the interlaboratory comparison; b) One or more items are sourced by the coordinator, assessed as appropriate, and distributed to the participants in an interlaboratory comparison with instructions; c) The participants conduct measurements, tests, examinations [12], or other work on the item(s) and report the results back to the coordinator; d) The coordinator evaluates the results and provides feedback to the participants; and e) The coordinator and/or the participants act on the results.

4. A proficiency testing provider may be requested by legislation to report an unsatisfactory result to a regulatory body (for example, a false negative result for a test of an infectious disease).

5. A coordinator of a material characterization study for a candidate reference material may decide to ask for some measurements to be repeated.

6. A coordinator of an interlaboratory method performance study may decide to recommend the issuing of a standard operating procedure.

7. Note 3:In some circumstances, one of the laboratories involved in an interlaboratory comparison may be the laboratory that provides the assigned value for the item. The assignment enables the determination of the metrological equivalence of measurement results of the participants but does not, by itself, establish metrological traceability [VIM 2.41].

8. Note 4:The minimum number of laboratories participating in an interlaboratory comparison will depend on the metrological properties of the measurement procedures used, for example, measurement precision [VIM 2.15] and analytical selectivity. See [28] section 5.4, performance characteristics of a measurement procedure.

9. Note 5:Determination of performance characteristics of a measurement procedure as part of procedure validation or characterization of a candidate reference material can be done by means of an interlaboratory comparison. (See method performance study and material characterization study.)

10. Note 6:Key comparisons and supplementary comparisons are organized by the International Bureau of Weights and Measures (BIPM) in support of the International Committee for Weights and Measures (CIPM) Mutual Recognition Arrangement (MRA) in which National Metrology Institutes demonstrate the international equivalence of their measurement standards [VIM 5.1] and the calibration certificates and measurement certificates they issue [92].

11. Note 7:Accredited laboratories and laboratories seeking accreditation are expected to participate in interlaboratory comparisons, for example, proficiency testing schemes, where available and appropriate.

12. Note8:The use of terms such as “ring test”, “round robin”, “intercalibration”, “intercomparison”, “collaborative study”, etc. for interlaboratory comparisons is not recommended in formal documents.

4.108 intermediate precision limit

See: precision limit.

4.109 internal quality control (IQC)

Quality control within a specified laboratory.

4.110 intralaboratory comparison

Organization, performance, and evaluation of measurements or tests on the same or similar items within the same laboratory in accordance with predetermined conditions.

1. [23].

4.111 laboratory information management system (LIMS)

laboratory information system (LIS)

Information system which can provide services to one or more measuring systems [VIM 3.2].

1. [68, 93].

2. Note 1:Services include the control of automated analyses and collecting, processing, storing, and managing of data.

3. Note 2:LIMS functionality can include sample registration and tracking (through barcodes, chips, etc.), electronic laboratory notebooks, report generation, quality control, and financial control.

4. Note 3:In laboratory medicine, the term “Laboratory Information System” is common.

4.112 material characterization study

Intralaboratory comparison or interlaboratory comparison with the aim of assigning a reference quantity value [VIM 5.18] to a quantity [VIM 1.1] with stated measurement uncertainty [VIM 2.26] or value to a reference nominal property value with stated examination uncertainty [12].

1. A material characterization study often utilizes selected (routine or reference) laboratories to measure quantity values of a candidate reference material by measurement procedure(s) judged most likely to provide the smallest associated measurement uncertainty.

2. Although proficiency testing is not primarily intended as a material characterization study, reference materials are sometimes certified on the basis of results from a proficiency testing scheme after appropriate quality assurance procedures.

4.113 matrix reference material

Reference material that is characteristic of a real sample.

1. Note 1:Matrix reference materials may be obtained directly from biological, environmental, or industrial sources.

2. Note 2:Matrix reference materials may also be prepared by a spike of the component(s) of interest into an existing material.

3. Note 3:A chemical substance dissolved in a pure solvent is not a matrix reference material.

4. Note 4:Matrix reference materials are intended to be used in conjunction with the chemical analysis of real samples of the same or a similar matrix.

5. Source: [2].

6. Soil, drinking water, metal alloys, and blood which fulfil the requirements of a reference material.

4.114 measurement capability

Ability to measure a quantity [VIM 1.1] in a specified interval of quantity values [VIM 1.19], embodied in a specified material, as demonstrated by measurement uncertainty [VIM 2.26].

1. Note: A comparison of the measurement uncertainty in the measurement result [VIM 2.9] obtained by one laboratory to that of the measurement result obtained by another laboratory for the same quantity in the same material compares their respective measurement capabilities.

2. [60].

4.115 measurement precision control material

precision control material

Quality control material with or without reference quantity value [VIM 5.18] used in quality control to assess measurement precision [VIM 2.15].

1. [1] entry 5.13 Note 2.

4.116 measurement trueness control material

trueness control material

Quality control material with reference quantity value [VIM 5.18] used in quality control to estimate a systematic measurement error [VIM 2.17].

1. [1] entry 5.13 Note 2.

4.117 method performance study

Intra- or interlaboratory study of one or more performance characteristics of a measurement procedure.

1. Note 1:The study is normally conducted in the frame of procedure validation or procedure verification.

2. Note 2:Details regarding organizing and conducting the study, for example, type of samples and number of measurements, are specified in a validation plan or in a protocol for interlaboratory comparison.

3. Note 3:The general term “collaborative study” should not be used for an interlaboratory method performance study.

4. [57, 94].

4.118 organization

Person or group of people that has its own functions with responsibilities, authorities, and relationships to achieve its objectives.

1. Note: The concept of ‘organization’ includes, but is not limited to, sole-trader, company, corporation, firm, enterprise, authority, partnership, association, charity, or institution, or part or combination thereof, whether incorporated or not, public or private.

2. [62].

3. Note 2: In formal documents, the term “body” is often used to denote an organization, for example, “accreditation body”, “certification body”, “inspection body”, “legislative body”, and “regulatory body”.

4.119 out-of-control criteria

Set of decision rules for identifying the presence of special causes.

1. Note 1: Decision rules may include those relating to measured quantity values [VIM 2.10] inside and outside of control limits in a control chart. They cover runs, trends, cycles, periodicity, concentration of points near the centre line or control limits, unusual spread of points within control limits (large or small dispersion), and relationships among values within subgroups.

2. [4] entry 2.2.8.

3. Note 2: Examples of decision rules and guidelines for the daily interpretation of a control chart are provided by Nordtest [39].

4.120 participant in an interlaboratory comparison

participant

Laboratory, organization, or person that receives test items and submits results for review by the coordinator of an interlaboratory comparison.

1. [30].

4.121 performance characteristic of a measurement procedure

performance characteristic of a measurement method

performance characteristic

Aspect of a measurement procedure that may be quantitatively investigated and assessed as part of procedure validation.

1. Note 1: Performance characteristics that may be considered in procedure validation are analytical selectivity, sensitivity of a measuring system, working interval, ruggedness of a measurement procedure, linearity of a measuring system, linearity of calibration, critical value, limit of detection, limit of quantification, measurement trueness [VIM 2.14], and measurement precision [VIM 2.15].

2. Note 2: Measurement uncertainty [VIM 2.26] is not a performance characteristic of a particular measurement procedure but a property of the measurement result [VIM 2.9] obtained using that measurement procedure.

3. [20, 31].

4.122 performance score

performance statistic

Statistic, derived from a result reported by a participant in a proficiency testing scheme, used in interpretation of participant performance and to allow comparison with defined objectives.

1. Note 1: The purpose of a performance score is to express the deviation of the reported value from the assigned value in a proficiency testing scheme in a manner that allows comparison with performance criteria.

2. Note 2: Names and defining equations of frequently used performance scores are listed in Table 4.122-1. Their definitions and interpretations are given in ISO/IEC 17043 [30] and ISO 13528 [28].

3. [28].

4.123 precision limit

Quantity value [VIM 1.19], less than or equal to what the absolute difference between two measured quantity values [VIM 2.10] obtained under specified conditions of measurement is expected to be with a given probability.

1. [95].

2. Note 1:ISO 3534-2 [4] defines three kinds of precision limit: repeatability limit (r), intermediate precision limit, and reproducibility limit (R) obtained under repeatability conditions of measurement, intermediate precision conditions of measurement [VIM 2.22], and reproducibility conditions of measurement [VIM 2.24], respectively. The recommended probability is 95 %.

3. Note 2:Precision limit at approximately 95 % is estimated by multiplying the standard deviation obtained under the specified conditions of measurement by 2√2.

4.124 procedure validation

method validation

Process of defining an analytical requirement and confirming that the procedure under consideration has capabilities consistent with that requirement.

1. Note 1:Inherent in procedure validation is the need to evaluate performance characteristics of a measurement procedure.

2. Note 2:The corresponding term in ISO 15189 [55] is “validation of examination procedures”.

3. Note 3:In ISO/IEC 17025 [23], the term “method” is used as a synonym for measurement procedure.

4. Note 4:Procedure validation is either done in a single laboratory or in the framework of an interlaboratory comparison.

5. [20].

4.125 procedure verification

method verification

Confirmation, through the provision of objective evidence, that the procedure fulfils specified requirements.

1. Note 1:A laboratory that implements a procedure described in, for example, an international standard or in a manufacturer’s documentation needs to verify that the procedure fulfils the specified requirements.

2. Note 2:The corresponding term in ISO 15189 [55] is “verification of examination procedures”.

3. Note 3:In ISO/IEC 17025 [23], the term “method” is used as a synonym for measurement procedure.

4. [20].

4.126 process in a state of statistical control

process in statistical control

stable process

Process subject only to random causes.

1. Note 1:The random variation is considered to follow a Gaussian distribution and is characterized by its variance (standard deviation)

2. Note 2:This state does not imply that the random variation is large or small, within or outside of specification, but rather that the variation is predictable using statistical techniques.

3. Note 3:A control chart can be used to monitor a process and to determine whether the process is, or is not, in a state of statistical control. See out-of-control criteria and control limit.

4. [4, 22].

4.127 proficiency test item

PT item

Sample, product, artefact, reference material, piece of equipment, measurement standard [VIM 5.1], data set, or other information used for proficiency testing.

1. [30] entry 3.8.

4.128 proficiency testing (PT)

Evaluation of the performance of a participant in an interlaboratory comparison against pre-established criteria.

1. Note 1: Proficiency testing is achieved by the distribution of proficiency test items for unsupervised measurement or examination [12] by the participants.

2. Note 2: Participation in proficiency testing schemes is not a substitute for internal quality control measures or vice versa.

3. Note 3: The evaluation of quantitative results of a participant in a proficiency testing scheme may be given as a z score, z’ score, ζ score, or E_n score (see performance score).

4. Note 4: The term “proficiency testing” includes, but is not limited to, a) quantitative scheme—where the objective is to quantify one or more measurands of the proficiency test item; b) qualitative scheme—where the objective is to identify or describe one or more characteristics of the proficiency test item; c) sequential scheme—where one or more proficiency test items are distributed sequentially for testing or measurement and results returned to the proficiency testing provider at intervals; d) simultaneous scheme—where proficiency test items are distributed for concurrent testing or measurement within a defined time period; e) single occasion exercise—where proficiency test items are provided on a single occasion; f) continuous scheme—where proficiency test items are provided at regular intervals; g) sampling—where samples are taken for subsequent chemical analysis; and h) data transformation and interpretation—where sets of data or other information are furnished and the information is processed to provide an interpretation (or other outcome).

5. Note 5: Some proficiency testing providers in the laboratory medicine area use the term “external quality assessment (EQA)” for their proficiency testing schemes or for their broader programmes, or both.

6. [30] entry 3.7.

4.129 proficiency testing provider

PT provider

Organization which takes responsibility for all tasks in the development and operation of a proficiency testing scheme.

1. [30] entry 3.9.

4.130 proficiency testing round

PT round

Single complete sequence from distribution of proficiency test items to reporting of the evaluation results to the participants. (See participant in an interlaboratory comparison).

1. [30] entry 3.10.

4.131 proficiency testing scheme

PT scheme

Proficiency testing designed and operated in one or more proficiency testing rounds for a specified area of testing, measurement, calibration [VIM 2.39], or inspection.

1. Note 1: A proficiency testing scheme might cover a particular type or number of tests, measurements, calibrations or inspections on proficiency test items.

2. [30] entry 3.11.

3. Note 2: The use of terms such as “ring test”, “round robin”, “intercalibration”, “intercomparison”, “collaborative study”, etc. for proficiency testing schemes is not recommended in formal documents.

4.132 protocol for interlaboratory comparison

Detailed set of instructions describing the objectives, design, conduct, and reporting of an interlaboratory comparison.

4.133 quality

Degree to which a set of inherent characteristics of an object fulfils requirements.

1. Note 1: The term “quality” can be used with adjectives such as poor, good, or excellent.

2. Note 2: “Inherent”, as opposed to “assigned”, means existing in the object.

3. [62].

4. Note 3: Measurement uncertainty [VIM 2.26] provides a quantitative measure of the quality of a measurement result [VIM 2.9].

4.134 quality assurance (QA)

Part of quality management focused on providing confidence that specified requirements for quality will be fulfilled.

1. [62]. Entry replaces recommendation in [21] p 2208.

4.135 quality control (QC)

Part of quality management focused on fulfilling specified requirements for quality.

1. [62]. Entry replaces recommendation in [96] p 1535 and [21] p 2208.

4.136 quality control material

control material

Material used for the purposes of quality control and subjected to the same or part of the same measurement procedure as that used for analytical samples.

1. Note:Blank materials, analytical samples, reference materials, and certified reference materials [VIM 5.14] can be used as quality control materials.

2. [82, 97].

4.137 quality improvement

Part of quality management focused on increasing the ability to fulfil requirements for quality.

1. Note:The requirements can be related to any aspect such as effectiveness, efficiency, or object traceability.

2. [62].

4.138 quality management

Coordinated activities to direct and control an organization with regard to quality.

1. Note:Quality management can include establishing quality policies and quality objectives.

2. [62].

4.139 quality management system

Part of a set of interrelated or interacting elements of an organization to establish quality policies and quality objectives and processes to achieve those objectives.

1. [62].

2. Note 1: A laboratory’s structure, roles and responsibilities, planning, operation, practices, rules, and beliefs are also established within the quality management system.

3. Note 2: Other common parts of a laboratory’s management system are financial management and environmental management. These management systems should not be confused with a laboratory information management system.

4.140 quality manual

Specification for the quality management system of an organization.

1. Note:Quality manuals can vary in detail and format to suit the size and complexity of an individual organization.

2. [62].

4.141 quality objective

Result to be achieved related to quality.

1. Note 1: Quality objectives are generally based on the quality policy of the organization.

2. Note2: Quality objectives are generally specified for relevant functions, levels and processes in the organization.

3. [62].

4. Note 3: In the context of quality management systems, quality objectives are set by the laboratory, consistent with the quality policy, to achieve specific results.

4.142 quality plan

Specification of the procedures and associated resources to be applied when and by whom to a specific object.

1. Note 1: These procedures generally include those referring to quality management processes and to product and service realization processes.

2. Note 2: A quality plan often refers to parts of the quality manual or to procedure documents.

3. Note 3: A quality plan is generally one of the results of quality planning.

4. [62].

4.143 quality planning

Part of quality management focused on setting quality objectives and specifying necessary operational processes and related resources to achieve the quality objectives.

1. Note: Establishing quality plans can be part of quality planning.

2. [62].

4.144 quality policy

Intentions and direction of a laboratory as formally expressed by its top management related to quality.

1. Note: Generally, the quality policy is consistent with the overall policy of the laboratory, can be aligned with the laboratory’s vision and mission, and provides a framework for the setting of quality objectives.

2. [62].

4.145 reference laboratory

Laboratory that applies a reference measurement procedure [VIM 2.7], a reference examination procedure [12], or performs a calibration [VIM 2.39].

1. The term “reference laboratory” may have other connotations in a national context.

2. In laboratory medicine, a reference measurement laboratory is defined in ISO 15195 [71].

4.146 reference material (RM)

Material, sufficiently homogeneous and stable with reference to specified properties, which has been established to be fit for its intended use in measurement or in examination of nominal properties [VIM 1.30].

1. Note 1: Examination of a nominal property provides a nominal property value and associated examination uncertainty.

2. Note 2: Reference materials with or without assigned quantity values [VIM 1.19] can be used for measurement precision [VIM 2.15] control, whereas only reference materials with assigned quantity values can be used for calibration [VIM 2.39] or measurement trueness [VIM 2.14] control.

3. Note 3: ‘Reference material’ comprises materials embodying quantities [VIM 1.1] as well as nominal properties.

4. Examples of reference materials embodying quantities:

   1. water of stated purity, the dynamic viscosity of which is used to calibrate viscometers;

   2. human serum without an assigned quantity value for the amount-of-substance concentration of the inherent cholesterol, used only as a measurement precision control material;

   3. fish tissue containing a stated mass fraction of a dioxin, used as a calibrator [VIM 5.12].

5. Examples of reference materials embodying nominal properties:

   1. colour chart indicating one or more specified colours;

   2. DNA compound containing a specified nucleotide sequence;

   3. urine containing 19-androstenedione.

6. Note 5: Some reference materials have assigned quantity values that are metrologically traceable to a measurement unit [VIM 1.9] outside a system of units [VIM 1.13]. Such materials include vaccines to which International Units (IU) have been assigned by the World Health Organization.

7. Note 6: In a given measurement, a given reference material can only be used for either calibration [VIM 2.39] or quality assurance.

8. Note 7: The specified requirements of a reference material should include its material traceability, indicating its origin and processing [98].

9. Source: [VIM 5.13] with Notes 4 and 8 omitted. See also: material stability, material homogeneity, and fitness for purpose. For Note 1, see [12] entry 3.9. For Note 2, see also property value assignment, conventional quantity value, and measurement trueness control material. For Note 3 Example 1a, see chemical purity. For Note 7, see also object traceability.

10. Note 9: The ‘product information sheet’ is a document containing all the information that is essential for using a reference material [2].

11. Note 10: Good practice in using reference materials and certified reference materials [VIM 5.14], in particular in measurement processes, is described in ISO Guide 33 [97].

Entry replaces recommendation in [21] p 2210.

4.147 reference material certificate

Document, issued by a reference material producer, containing the essential information for the use of a certified reference material [VIM 5.14] and confirming that the necessary procedures have been carried out to ensure the validity and traceability of the stated property values.

1. Note 1: A reference material certificate is usually valid for a stated period of time (‘period of validity’ or as described by its ‘expiry date’), which defines the shelf life of the certified reference material.

2. Note 2: Documents containing the information described above may not, for legal or other (non-technical) reasons, be termed “certificate” (compare Note 1 to certified reference material).

3. Note 3: ISO Guide 31 [61] is the guidance document to the required and recommended content of a reference material certificate.

4. Note 3: In this definition, “traceability” covers both metrological traceability [VIM 2.41] of a measurement result [VIM 2.9] and examination traceability [12], but not object traceability.

5. [2, 48, 61].

4.148 reference material certification

certification of a reference material

Process that formally establishes the certified property value(s) of a candidate certified reference material.

1. Note 1: The process is the responsibility of the reference material producer.

2. Note 2: Properties of a material include qualitative properties such as identities of chemical substances and quantitative properties such as mass concentration.

3. Note 3: The outcome of the process is a reference material certificate.

4. Note 4: Reference material certification is a ‘first-party attestation’ in accordance with the definition of the term “declaration” (see [65] section 5.4).

5. [2].

4.149 reference material certification report

certification report

Document giving detailed information, in addition to that contained in a reference material certificate.

1. Note:The information may refer to, for example, the preparation of the reference material, measurement procedures, factors affecting measurement accuracy [VIM 2.13], statistical treatment of measurement results [VIM 2.9], and the way in which metrological traceability [VIM 2.41] was established.

2. [2, 48, 61].

4.150 reference material producer

RM producer

Technically competent body that produces a reference material compliant with the appropriate guidance documents and issues the reference material documentation.

1. Note 1: ‘Body’ refers to an organization.

2. Note 2: The relevant guidance documents are the ISO Guides 31 [61] and 35 [48].

3. Note 3: ISO 17034 [51] provides the general requirements for the competence of reference material producers.

4. [2].

4.151 rejection interval

rejection zone

Interval of non-permissible measured quantity values [VIM 2.10].

1. [70] entry 3.3.10.

2. Note: Non-permissible measured quantity values are associated with items that do not conform to specified requirements and lie outside the acceptance interval.

See also: [69], conformity assessment.

4.152 repeatability limit, r

See: precision limit.

4.153 reproducibility limit, R

See: precision limit.

4.154 requirement

Need or expectation that is stated, generally implied or obligatory.

1. ‘Generally implied’ means that it is custom or common practice for the organization and interested parties that the need or expectation under consideration is implied.

2. A specified requirement is one that is stated, for example, in documented information.

3. [62].

4.155 ruggedness of a measurement procedure

robustness of a measurement procedure

Ability of a measurement procedure to maintain acceptable performance under minor changes in operating conditions.

1. Note 1: Ruggedness is normally investigated as a part of procedure development and may be part of procedure validation.

2. Note 2: The outcome of a ruggedness test provides objective evidence of the applicability of the measurement procedure during normal usage.

3. Note 3: A measurement procedure, the performance of which remains unaffected by minor changes in operating conditions, is usually said to be “rugged” or “robust”.

4. [20].

4.156 sensitivity of a measuring system

analytical sensitivity

sensitivity

Quotient of the change in an indication [VIM 4.1] of a measuring system [VIM 3.2] and the corresponding change in a quantity [VIM 1.1] being measured.

1. Note 1: Sensitivity of a measuring system can depend on the value of the quantity being measured.

2. Note 2: The change considered in a value of a quantity being measured must be large compared with the resolution [VIM 4.14].

3. [VIM 4.12].

4. Note 3: Sensitivity of a measuring system can be obtained from the slope of the calibration curve.

5. Note 4: Sensitivity of a measuring system should not be confused with diagnostic sensitivity in laboratory medicine.

6. Note5: Sensitivity of a measuring system should not be confused with limit of detection or limit of quantification.

See [20]. Entry replaces recommendation in [21] p 2167. See also: selectivity of a measuring system [VIM 4.13].

4.157 Shewhart control chart

Control chart with Shewhart control limits intended primarily to distinguish between the variation in the plotted measure due to random causes and that due to special causes.

1. [4]. See also: [83].

4.158 Shewhart control limit

Control limit determined statistically from the variation of the process due to random causes alone.

1. [81]. See also: [83].

4.159 Shewhart means chart

Shewhart control chart in which the means of measured quantity values [VIM 2.10] are plotted against time.

1. A Shewhart means chart with mean values from a process in a state of statistical control with a simulated change in the process mean after 10 days is shown in Fig. 4.159-1.

2. Note: Nordtest [82] terms a control chart with measured quantity values [VIM 2.10] scaled by the mean or target value an “X-chart”. ISO uses the term “X-control chart” for a control chart which plots single values [81] entry 3.17.

3. Source: [83].

Fig. 4.159-1:

Shewhart means chart of the means of duplicate analyses of a quality control material, twice per day (d) over 20 days. Each point is the mean of the day’s four results (n = 4). Upper and lower warning limits (UWL and LWL) are at x‾ ± 2s/√n, where x‾ is the process mean, s is the standard deviation under repeatability conditions of measurement, and upper and lower action limits (UAL and LAL) are at x‾ ± 3s/√n. A simulated measurement bias [VIM 2.18] of one standard deviation is applied after day 10.

4.160 Shewhart range chart

Shewhart control chart in which the ranges of measured quantity values [VIM 2.10] are plotted against time.

1. Note 1: The range is the greatest measured quantity value minus the least measured quantity value.

2. Note 2: Warning and action limits are given in tables (for example, [83] 6.1) as a function of the number of measured quantity values (n) taken to obtain the range and of the expected average range.

3. Note 3: Nordtest [82] p 13 advises that for Shewhart range charts, the best samples to be used are test samples selected from among the samples to be analysed in that analytical run.

4. [83].

4.161 specified requirement

Need or expectation that is stated.

1. [70] entry 3.3.3

4.162 standard deviation for proficiency assessment, σ_PT

Measure of dispersion used in the evaluation of results of proficiency testing.

1. Note: Not all proficiency testing schemes evaluate proficiency based on the dispersion of results.

2. [28] entry 3.4.

4.163 standard operating procedure (SOP)

recommended operating procedure (ROP)

standard method

Authorized, documented procedure or set of procedures with detailed instructions for specified activities.

1. Note: Laboratory activities for which standard operating procedures are issued include sampling, measurement, testing, and examination [12].

2. [99].

4.164 statistical process control (SPC)

Activities focused on the use of statistical techniques to reduce variation, increase knowledge about the process, and steer the process in the desired way.

1. Note: Although statistical process control originally was concerned primarily with manufactured goods, it is also equally applicable to processes producing services, for example, a measurement procedure.

2. [4].

4.165 target measurement uncertainty

target uncertainty

measurement uncertainty [VIM 2.26] specified as an upper limit and decided on the basis of the intended use of measurement results [VIM 2.9].

1. [VIM 2.34].

2. Note: Setting and using target uncertainty is described in [100].

4.166 tolerance

specified tolerance

Difference between upper and lower tolerance limits.

1. [70] entry 3.3.6. See also: conformity assessment.

2. Note: Tolerance should not be confused with measurement uncertainty [VIM 2.26].

4.167 tolerance interval

specification zone

Interval of permissible quantity values [VIM 1.19].

1. Note 1: Unless otherwise stated in a specified requirement, the tolerance limits belong to the tolerance interval.

2. Note 2: The term “tolerance interval” as used in conformity assessment has a different meaning from the same term as it is used in statistics.

3. [70] entry 3.3.5. See also: [69], conformity assessment.

4. Note 3: A permissible quantity value of a specified quantity [VIM 1.1] is required of an item fulfilling a specified requirement.

5. Note 4: Permissible quantity values must not be confused with permissible measured quantity value of an acceptance interval.

4.168 tolerance limit

specification limit

Specified upper or lower bound of permissible quantity values [VIM 1.19] of a property.

1. [70] entry 3.3.4. See also: conformity assessment.

4.169 total quality management (TQM)

Organization-wide efforts to install a permanent climate in which an organization continuously improves its ability to deliver high-quality products and services to customers.

1. [85].

4.170 validation

Confirmation, through the provision of objective evidence, that the requirements for a specific intended use or application have been fulfilled.

1. Note 1: The objective evidence needed for a validation is the result of a test or other form of determination such as performing alternative calculations or reviewing documents.

2. Note 2: The term “validated” is used to designate the corresponding status.

3. Note 3: The use conditions for validation can be real or simulated.

4. [62].

5. Note 4: In the VIM [1], ‘validation’ is defined as “verification, where the specified requirements are adequate for an intended use”.

4.171 verification

Confirmation, through the provision of objective evidence, that specified requirements have been fulfilled.

1. Note 1: The objective evidence needed for verification can be the result of an inspection or of other forms of determination such as performing alternative calculations or reviewing documents.

2. Note 2: The activities carried out for verification are sometimes termed “qualification process”.

3. Note 3: The term “verified” is used to designate the corresponding status.

4. [62] entry 3.8.12.

5. Note 4: In the VIM [1], ‘verification’ is defined as “provision of objective evidence that a given item fulfils specified requirements”.

4.172 Youden plot

Graphical technique for evaluating an interlaboratory comparison when each participant has made two measurements on the same sample or one measurement on each of two different samples.

1. The coordinates of each point may be the measured quantity values [VIM 2.10] themselves or any transformation thereof such as a performance score, for example, a z score (see Fig. 4.172-1).

2. The Youden plot is a simple but effective method for comparing both within-laboratory variability and between-laboratory variability.

Fig. 4.172-1:

Youden plot of the z scores of samples #9 and #10 of Round 5 of U39 of the proficiency testing program held by the RCPA Australia for the analysis of creatinine in urine by 218 laboratories. (Reproduced from [101] with permission).