Startseite Chiral and Achiral Enantiomeric Separation of (±)-Alprenolol
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Chiral and Achiral Enantiomeric Separation of (±)-Alprenolol

  • M.M. López Guerrero EMAIL logo , A. Navas Díaz , F. García Sánchez und H. Corrall
Veröffentlicht/Copyright: 12. Juni 2019
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Open Chemistry
Aus der Zeitschrift Open Chemistry Band 17 Heft 1

Abstract

The chiral separation of enantiomers is crucial for pharmacovigilance within drug discovery. Although a large number of prescribed medications are marketed as pure enantiomers, this is not always the case and many are in fact racemic mixtures. Drug scandals, such as that of Thalidomide in 1961, provide a clear example of the social and economic repercussions that can be caused by negligence of these chiral compounds. Two high performance liquid chromatography (HPLC) methods are presented to determine, separate and quantitate a commonly prescribed chiral beta blocker, (-)-Alprenolol. The first method utilises a chiral column to physically separate the two enantiomers of Alprenolol in 25 minutes, before quantitating with two detectors. Fluorimetry gave the better limit of detection of 0.16-0.41ng and a correlation coefficient of 0.999. The second method used an achiral column coupled with polarimetry to quantitate (-)-Alprenolol without the need for physical separation in 10 minutes. The limit of detection achieved was 27-37μg and demonstrated a correlation coefficient of -0.999.

Keywords: Separation; Enantiomer; Chiral; Achiral; HPLC

1 Introduction

Beta blockers impede the effects of epinephrine and norepinephrine within cardiac and smooth muscle resulting in a decrease in heart rate and blood pressure [1]. Alprenolol is a non-polar beta blocker commonly prescribed for the treatment of cardiovascular presentations such as hypertension, angina and cardiac arrythmia [2,3,4]. Numerous substances found in nature, many of them pharmaceutical medicines such as Alprenolol, are chiral [5]. Typically, only one enantiomer is therapeutically active, and the other is either inactive or toxic. This was highlighted in the media by the 1961 Thalidomide drug scandal, which demonstrated a further need for research into the separation of these two enantiomeric forms [6,7]. It has been verified that for beta blockers, including Alprenolol, the pharmacokinetics differ greatly between the two enantiomers [8]. For a class of drug that is marketed as a “racemic dose”, only the (-)-Alprenolol accounts for the majority of the beta blocking activity [9]. A large number of pharmaceutical products are sold under the ruse of being pure enantiomers but are still in fact racemic mixtures [10]. As a result, changes to pharmaceutical manufacturing guidelines aim to increase safety and subsequently avoid the reoccurrence of similar scandals [11]. This has led to a greater need for robust, reliable and high throughput analytical techniques to be developed for enantiomeric separation and detection.

Attempts at the resolution of enantiomeric forms of Alprenolol and other beta blockers has been done previously using capillary electrophoresis (CE) [12,13], micellar electrokinetic chromatography (MEKC) [14,15], capillary isotachophoresis coupled with nuclear magnetic resonance (cITP/NMR) [16], nano-LC [11] and HPLC with an acid glycoprotein (AGP) column [3,17, 18, 19]. These previous citations, however, have demonstrated various limitations such as poor sensitivity, inability to identify low purity chiral samples and lengthy method preparations [3,16, 17, 18, 19]. The ability of chromatographic methods to simultaneously separate, analyse and quantitate a multitude of substances within a mixture demonstrates their superiority over other analytical techniques [20]. While HPLC is an analytical technique that is rarely surpassed in achieving separation, one of the most difficult challenges it has faced is perfecting the resolution of enantiomers [21]. As a result of the rise in demand to characterise enantiomers and determine their purities, the development of new methods for the separation of a wide range of enantiomers has progressed rapidly [22, 23, 24].

There are two routes that can be taken with chiral separation by HPLC. Firstly, the use of a chiral column with standard detection and secondly the use of an achiral column with a chiral detector. Both methodologies will be investigated in this study. The advantages of a chiral HPLC method are that the high sensitivity of standard HPLC detectors, such as UV-Vis and Fluorescence, can be applied to chiral mixtures [3]. For the chiral opportunity, cyclodextrins (CDs) were employed as the chiral selector for the racemic separation, as compared to other selection options they offer many advantages [11]. The geometric arrangement of the molecule on the inner surface of the column creates a hydrophobic cavity to allow for chiral selectivity and the formation of inclusion complexes [25]. The size, polarity and structure of the guest analyte within the CDs surface all influence the formation of this inclusion complex, however if the molecular fit of the analyte is efficient then the chiral recognition will be more selective [26,27]. It has previously been reported that the presence of aromatic rings, such as that found within the structure of Alprenolol, increases the likelihood of inclusion complexes to develop [28]. Due to their opposite three-dimensional configurations the enantiomers of racemic mixtures associate differently with the cyclodextrin molecules and form inclusion complex diastereomers. It is expected in this case that there will be hydrophilic interactions between the C2 and C3 of the hydroxyl groups on the CD and the Alprenolol structure [29]. This type of column is characteristic for its enantioselectivity and is known for its elite separation of enantiomers and different pharmaceutical ingredients [30].

For the achiral method development, in-line polarimetry is chosen to distinguish the enantiomers as well as fluorescence and photometry for comparison. Although known for its low sensitivity up against the more commonly chosen detectors, such as a UV-Visible (UV-Vis) and Diode Array (DAD), polarimetry offers chiroptic data to explicitly separate and determine the identity of the enantiomers without the need for prior separation [31,32]. To the best of the authors knowledge the present study is the first to report two HPLC methods, one chiral and one achiral, capable of fully resolving racemic Alprenolol.

2 Experimental

2.1 Chemicals and Reagents

Racemic Alprenolol and (-)-Alprenolol Hydrochloride (1-(o-Allylphenoxy)-3-(isopropylamino)-2-propanol hydrochloride) >98% were purchased from Sigma Aldrich, UK. Analytical grade Acetonitrile (ACN), Ethanol (EtOH), Glacial Acetic Acid, Trifluoroacetic Acid (TFA) and Triethylamine (TEA) were supplied by Merck, UK. LiChrosolv® Ultrapure Grade Methanol (MeOH) was supplied by Merck, UK. LC grade water (H2O) was prepared by passing de-mineralised water through a Milli-Q filtration system (Millipore, Bedford, MA).

2.2 Instrumentation

The chiral LiChroCART® 250-4 ChiraDex® (5μm) (Merck, UK) and the achiral Supelco LiChrospher® RP-8 125-4 (5μm) (Sigma, UK) chromatographic columns were tested. The flow rates used were in the ranges recommended by the manufacturers; 0.7mL/min for the chiral LiChroCART® column, and 1.0mL/min for the achiral LiChrospher®.

All measurements were achieved using a Hitachi-Merck (Darmstadt, Germany) high performance liquid chromatograph (HPLC) consisting of the following modules; a L6200 pump, an AS-4000 autosampler and a D-6000 interface. While the chiral stationary phase was in use, the following modules were coupled together; an L-4250 UV-visible detector (UV-Vis) and F-1080 fluorescence detector. The injection volume was set at 20μL. When the achiral stationary phase was applied, the F-1080 fluorescence detector and L-4250 UV-visible detector (UV-Vis) are employed alongside a ChiraMonitor® 2000 polarimeter. All integrations and instrument parameters were controlled with Hitachi-Merck HM software. Analog optical rotation data acquired from the ChiraMonitor® 2000 was transformed to digital by the Pico ADC-100 (Picotechnology Ltd., Cambridge, UK). The fluorescence detector was set at 230nm (absorption), 278nm (excitation) and 400nm (emission). The polarimeter laser was set, as described by Lloyd [33], providing 30mW of light at 830nm. The injection volume was set at 12μL. All injections were done in triplicate.

2.3 Chromatographic Conditions

The optimised reverse-phase chiral chromatographic separation was achieved with a total run time of 25 minutes. Experimentation used an isocratic gradient, with a mobile phase comprised of ACN:MeOH:Triethylamine:Acetic Acid (98:2:0.2:0.4, v/v). Flow rate was set at 1mL/min. The (+) and (-)-Alprenolol were identified based on standard retention times.

The optimised reverse-phase achiral chromatographic separation was achieved with a total run time of 10 minutes. Again, an isocratic gradient was used, with a mobile phase consisting of Methanol:Water:TFA (50:50:0.4, v/v). Flow rate was set at 0.7mL/min. The (+)and (-)-Alprenolol were identified based on their optical rotation as identified by polarimetric data.

All solvents were filtered through a 0.2-micron filter and degassed in an ultrasonic bath prior to analysis. The column temperature was controlled at room temperature in both instances.

2.4 Mobile Phase and Sample Preparation

Standard stock solutions of the (-)-Alprenolol and Racemic (±)-Alprenolol were prepared respectively at a concentration of 15mg/mL in methanol. The racemic (±)-Alprenolol was diluted appropriately with methanol to create five calibration standards utilised for the chiral method, based on the known sensitivity of the detectors. Calibration standards for the achiral method were made by mixing the two stock solutions to contain 50, 55, 65, 75, 85 and 100% (-)-Alprenolol. All solutions were prepared weekly and stored in the fridge (4°C).

Ethical approval: The conducted research is not related to either human or animal use.

3 Results and Discussion

3.1 Determination of Alprenolol Enantiomers using a Chiral Column

3.1.1 Optimisation of the Mobile Phase

Chiral separations are very sensitive to changes in temperature, pH, ionic strength, polarity and composition of the mobile phase [34]. A small change in these parameters can cause drastic changes in the retention and resolution of compounds within a mixture. Careful control of the experimental conditions, therefore, is necessary to obtain reproducible results. Optimising the mobile phase, in particular, is a key parameter required to be controlled as it has such a large influence on the signal received by the detectors [35]. Changing the constituents of the mobile phase can have a vast impact on resolution of structurally related compounds when using reversed-phase HPLC [36,37]. In this case, however, the high basicity of Alprenolol leads to complex mobile phase manipulation.

Initial injections of the racemic mixture utilised ACN as the mobile phase, however both enantiomers were observed to have a high affinity for the column and eluted slowly. From these initial trial runs, although lengthy, the time of the injection peak was eluded (~3 minutes). Development from this point forward aimed to fully resolve the enantiomers, but with elution as close to the injection peak as possible to ensure a quick run time. The literature expresses enantioresolution as an advantage of mobile phase modifiers, for which primary alcohols such as MeOH are seen as far superior to branched alcohols such as isopropanol (IPA) [38,39,40]. MeOH, therefore, was added to the mobile phase in small incremental amounts over a series of injections. This demonstrated a decrease in the retention of the Alprenolol analytes as the ratio of MeOH to ACN increased. Unfortunately, with this, the resolution of the enantiomers decreased. The optimum ratio of ACN to MeOH was found to be 98:2, finding a compromise between retention on the stationary phase and resolution. Other modifiers, such as acid buffer, were also trialled as previous studies have demonstrated how enantioselectivity is dependent on pH [39,40]. Acetic acid was chosen as the buffer of choice, as it also improved peak tailing, with the best output in results seen at 0.4% [41]. The literature also discusses the advantages of mobile phase additives, explaining how the type and ratio selected can impact enantioselectivity and resolution [38,42]. TFA is known to have a dominant effect on chiral separations, however for more basic drugs TEA has been proven to demonstrate a higher success rate [38]. In light of this, 0.2% TEA was added to the mobile phase.

Retention times for the (-) and (+)-Alprenolol enantiomers were achieved at approximately 19 and 21 minutes (Figures 1 and 2). Due to broad peak shapes, complete baseline separation between the two enantiomers was not achieved (<0.8 USP Resolution, Peak Tailing >1.5) [43]. Regardless of further changes made to the mobile phase, including trial of a gradient and other method parameters, this resolution and peak shape could not be improved. Mechanisms for enantiomer separation are not clearly defined in the literature, however Pirkle & Pochapsky detail a three-point rule that requires at least three instantaneous stereochemical interactions between the chiral stationary phase and the analyte [44]. A lack of these published interactions between the stationary phase and the enantiomers could explain the subpar baseline resolution. Despite this, it was deemed that the method was acceptable for use, and development moved onto determination of enantiomeric purity.

Figure 1 Final chiral method parameters for the separation of Alprenolol racemic mixture using photometric detection. Elution of (-)-Alprenolol and (+)-Alprenolol were seen at ~19 and 21 minutes respectively.
Figure 1

Final chiral method parameters for the separation of Alprenolol racemic mixture using photometric detection. Elution of (-)-Alprenolol and (+)-Alprenolol were seen at ~19 and 21 minutes respectively.

Figure 2 Final chiral method parameters for the separation of Alprenolol racemic mixture using fluorescence detection. Elution of (-)-Alprenolol and (+)-Alprenolol were seen at ~19 and 21 minutes respectively.
Figure 2

Final chiral method parameters for the separation of Alprenolol racemic mixture using fluorescence detection. Elution of (-)-Alprenolol and (+)-Alprenolol were seen at ~19 and 21 minutes respectively.

3.1.2 Quantitation of Alprenolol Enantiomers

Early injections of the racemic mixture demonstrate that the peak heights/areas of the Alprenolol enantiomers are not identical. This is an immediate indication that the racemic mixture is not entirely racemic and does not contain exactly 50% of each enantiomer. Using the analytical signals received from the photometric and fluorometric detectors, alongside the method previously published by Sanchez et al., the ratio of each enantiomer in the sample can be determined [45]. Here, the peak height, molar absorption coefficient and the concentrations of each enantiomer in the racemic mixture are used to calculate the enantiomeric purity as 52.5% (-)-Alprenolol and 47.5% (+)-Alprenolol. These values assigned to each enantiomer within the racemic mixture were used to calculate the total μg of (±)-Alprenolol contained in each calibration standard. This transpires to be 49-75μg across the calibration range. Linearity was assessed at five levels between these two values.

Least squares regression has been discussed in the literature as the most commonly used multivariate regression method, particularly for building calibration models [46]. When compared with other multivariate regression models, the least squares method demonstrates a higher separation power as its algorithms are designed in such a way as to counteract the presence of predictor variables when there are relatively few samples [47]. The linear calibration model is most easily achieved by performing a linear least squares regression of the instrument response versus the mass of the analyte.

Calibration plots were generated to investigate the linearity of the method, by plotting the total peak area (or peak height) for both enantiomers against the total (±)-Alprenolol present in each calibration standard (μg). The tested standards were prepared according to the sensitivity of the detectors. Peak area calibration plots for photometric detection gave a correlation coefficient of 0.993, and fluorometric detection gave a correlation coefficient of 0.991 (Figures 3 and 4). Peak height calibration plots for photometric detection gave a correlation coefficient of 0.991, and fluorometric detection gave a correlation coefficient of 0.990.

Figure 3 Photometry calibration plot using peak area as a function of the total (±)-Alprenolol in each calibration standard (μg).
Figure 3

Photometry calibration plot using peak area as a function of the total (±)-Alprenolol in each calibration standard (μg).

Figure 4 Fluorescence calibration plot using peak area as a function of the total (±)-Alprenolol in each calibration standard (μg).
Figure 4

Fluorescence calibration plot using peak area as a function of the total (±)-Alprenolol in each calibration standard (μg).

It was also determined exactly how much of each enantiomer (μg) was present in the calibration standards, as a result of knowing the initial ratio in the racemic mixture. Calibration plots were therefore constructed using the individual enantiomer peak heights/areas instead of the combined values at each chosen calibration level. The regression equations, correlation coefficients and limits of detection generated for both enantiomers using the peak heights and areas with photometric and fluorometric detection are shown in Table 1.

Table 1

Calibration data for L (-) Alprenolol and D (+) Alprenolol (N = 3).

PhotometricFluorometric
Regression EquationCorrelationLoDRegression EquationCorrelationLoD
(y=m x +c)Coefficient (R2)(ng)(y=m x +c)Coefficient (R2)(ng)
L(-)Alprenolol Areay =12.35x + 313.180.991340y = 1275.96 x + 1808.280.9990.41
L(-)Alprenolol Heighty = 22.14x + 200.080.99626y = 1872.97x + 6353.840.9960.19
D(+)Alprenolol Areay = 15.95x + 373.450.941630y = 1640 x + 2236.630.9980.25
D(+)Alprenolol Heighty = 20.05x + 238.330.99436y = 1765.67x + 3114.940.9990.16

Results demonstrate that fluorometric detection, for both peak area and peak height, produce the best results. Limits of detection (LoD) were considered to be the calibration standards which produced signal-to-noise ratios of 3, as per ICH guidelines [43]. The LoD determined for the fluorescence signals were between 0.16-0.41ng, whereas those for the photometric signals were much higher with great variation between 26-630ng. Interestingly, although peak area typically gives better

results with chromatographic methods than peak height in terms of calibrations, the better limit of detection for the photometric results are those of the peak height [48]. This can be seen across both data sets, as the results derived from the peak heights deduct higher sensitivity than those of peak areas. The literature does suggest, however, that peak height can be more reliable when dealing with the lower end of a calibration set i.e. determination of limit of detection [49]. The correlation coefficients for both fluorescence and photometric detection are close to 1, but the data from the fluorescence detector is again superior.

3.2 Determination of Alprenolol Enantiomers using an Achiral Column

3.2.1 Optimisation of the Mobile Phase

Aside from the alternate column, another difference from the previous method is the detectors used. Polarimetry has a high dependence on many variables, including the composition of the mobile phase, the temperature, oscillations of the flow and the impurities of the solvents [50]. The selection of the mobile phase, specifically, is crucial since it intervenes in the optical rotation of the enantiomers in the polarimetric detector [51, 52, 53, 54]. Biot’s law states that this rotational power produced by an enantiomer will be directly proportional to the quantity of each enantiomer present and therefore the output signal given. This, in turn, has a direct effect on the sensitivity of the technique [54]. In a racemic mixture, however, the rotation being produced in the plane of polarised light by the positive enantiomer is counteracted by the rotation being produced by the negative enantiomer, which gives a final optical rotation of zero [52]. From this it could be inferred that the optical rotation produced by a sample of a chiral substance will be proportional to the difference in quantities of the two enantiomers and, therefore, their concentrations.

The mobile phase composition of the achiral method was optimised, similarly to the chiral method reported, by altering the buffers and mobile phase modifiers. Initial injections of the racemic mixture utilised MeOH as the mobile phase to analyse the retention of the enantiomers. MeOH was chosen over ACN as it is commercially cheaper, however the literature suggests that the RP column interactions are stronger than those of ACN, which leads to increased separation power of compounds [55]. Alprenolol was poorly retained by the column, however, and eluted prior to the injection peak (~2 minutes). The addition of water was investigated with the aim to increase the retention of the analytes on the column, therefore separating the injection peak and the Alprenolol. After various ratios of MeOH:H2O were trialled it was observed that there was a linear relationship between the ratio of water added to the mobile phase and the retention of the analyte on the column. This is a common relationship that has been observed in the literature since the 1990’s [56]. The optimal composition of mobile phase here was deemed to be MeOH:H2O 50:50. TFA was utilised as a mobile phase additive (0.4%) as it has been previously demonstrated to have a dominant effect on chiral separations for both acidic and basic chiral drugs [38].

It was identified that under these conditions the polarimetric detector was sufficiently sensitive, and two signals are obtained for the enantiomers at 7.08 minutes (425 secs) and 7.92 mins (475 secs). For the photometric and fluorescence detectors, a broad single peak for Alprenolol eluted at ~7 minutes indicating coelution of the two enantiomers, lending these detectors somewhat obsolete. This lack of physical separation of the enantiomers was expected due to the achiral nature of the RP-8 column, however the signals received from these detectors can still be used to determine the total amount of the enantiomers in a sample.

Unfortunately, as the polarimeter required a high sample concentration in order to get a signal observable over the high level of noise, the resulting peak of interest when detected using photometry and fluorescence has prominent tailing. The peak broadening is also increased further as a result of the columns inability to resolve the enantiomers. This will in turn cause deviations in the linearity of the response from these detectors, as they are close to their capability limits, and will therefore not be used for any calculations.

3.2.2 Determination of Alprenolol Enantiomeric Purity using an Achiral Column

Calibration standards, produced as detailed previously, were run on the now optimised achiral method. The calibrations plot the difference in polarimetric peak area or peak height of the two enantiomers as a function of the percentage of (-)-Alprenolol in the mixture. The calibrations for difference in peak height and peak area showed peak area to be the superior measurement, with a correlation coefficient of 0.996. The correlation coefficient for difference in peak height was 0.980. Both calibrations display a strong, robust correlation to the percentage of (-)-Alprenolol present in the sample, however the linearity of the method still requires improvement.

The calibration equations generated for the data sets shown were used to calculate the percentage of (-)-Alprenolol in the prepared racemic mixture at 51.8% (which would therefore put the (+)-enantiomer at 48.2%). Comparing these results to those obtained using the chiral column it is seen that they are very close; 52.5% with the chiral column and 51.8% with the achiral column. This initially suggests that these two methods are comparable with each other, however it cannot be said which is superior as the true value of the (-) and (+)-Alprenolol in the mixture is unknown.

3.2.3 Correcting Linearity Deviations from the Polarimetric Signal

Deviations of a polarimetric signal from ideal linearity can be demonstrated through an exploration of refractive index artefacts (RIA) and chemical law [54]. In order to eliminate these phenomena of measurements, corrections must be made to calibration equations [52,54]. As previously discussed, Biot’s law explains that the response from positive and negative enantiomers either counteract each other or give a response that indicates a higher presence of one enantiomer [54]. It would be logical to assume that this value is obtained only due to the effect of optical rotation, however, this is not entirely accurate [57]. Signals obtained from pure enantiomer injections give only positive values for (+)-enantiomers and only negative values for (-)-enantiomers, and as a result the effect of RIA is low compared to the analyte signal. The closer the ratio of the enantiomers in a mixture is to 50%, however, the greater the impact of these other factors [54]. Literature suggests that the main factors that influence RIA are the refractive index of the mobile phase, the analyte concentration and the flow of the mobile phase, all of which can be corrected [5]. RIA corrections were applied to each of the calibration points, and calibration equations updated. Excellent correlation coefficients of 0.999 for both peak area and peak height are achieved after reprocessing, further demonstrating the importance of applying RIA corrections to data obtained by polarimetric

detection. The negative correlation coefficients represent the negative correlation seen throughout the calibrations, with LoD seen between 27-37μg. The degree of RIA corrections can be seen in Figures 5 and 6.

Figure 5 Achiral calibration plots before and after RIA corrections, plotting the difference in polarimetric signal peak area as a function of L(-)-Alprenolol percentage.
Figure 5

Achiral calibration plots before and after RIA corrections, plotting the difference in polarimetric signal peak area as a function of L(-)-Alprenolol percentage.

Figure 6 Achiral calibration plots before and after RIA corrections, plotting the difference in polarimetric signal peak height as a function of L(-)-Alprenolol percentage.
Figure 6

Achiral calibration plots before and after RIA corrections, plotting the difference in polarimetric signal peak height as a function of L(-)-Alprenolol percentage.

The corrections eliminated any deviations in linearity due to the aforementioned effects and, as expected, the racemic mixture gives a signal difference of zero for both data sets. Using the corrected calibration lines, the percentage of (-)-Alprenolol in the racemic mixture is calculated. Based on the difference in area of the polarimetric signals 52.7% is obtained. The difference made when applying RIA corrections can be seen by comparing pre and post RIA results with that of the chiral method.

4 Conclusions

Previous attempts at the resolution of Alprenolol enantiomers, as well as other beta blockers, has been attempted but have demonstrated various limitations. Here, two high performance liquid chromatography methods are presented which separate and quantitate (±)-Alprenolol using chiral and achiral routes.

Mobile phase parameters such as mobile phase modifiers, acids and additives were investigated to achieve optimised chromatographic conditions. The (±)-Alprenolol analytes had a high affinity for the column under initial chiral conditions and eluted slowly. Development, leading to a final mobile phase of ACN:MeOH:TEA:Acetic Acid (98:2:0.2:0.4 v/v), allowed enantioresolution of the two compounds in 25 minutes.. The mobile phase manipulation for the achiral method was crucial due to the nature of the polarimetric detector. This method utilised Methanol:Water:TFA (50:50:0.4, v/v) to separate the (±)-Alprenolol enantiomers in just 10 minutes.

Using the developed chiral method, it was determined that the racemic (±)-Alprenolol standard did not contain equal quantities of both enantiomers. Peak height, molar absorption coefficient and the concentrations of each enantiomer were used to calculate enantiomeric purity at 52.5% (-)-Alprenolol. Least squares regression algorithms were used to investigate linearity of the method for each individual enantiomer. The analysis was carried out for both detectors using peak area/height versus mass of analyte. Fluorescence was deemed the far superior detector, achieving correlation coefficients between 0.996 and 0.999, and limits of detection between 0.16-0.14ng.

Calibrations standards were run on the optimised achiral method parameters to assess linearity of the method. Peak area was found to be the statistically superior variable over peak height in this instance with a correlation coefficient of 0.996, showing that the linearity of the method still required improvement. Linearity deviations from the polarimetric signal were corrected in order to eliminate refractive index artefacts, which produced updated correlation coefficients of 0.999, and limits of detection between 27-37ug. Enantiomeric purity, here, was determined to be 52.7% (-)-Alprenolol.

The calibration models for both methods demonstrated above acceptable limits, indicating their strength and utility. They present two ways to separate, detect and quantitate (±)-Alprenolol enantiomers although each with their limitations. The chiral method produces enantioresolution in 25 minutes with good limits of detection, although the unique columns can be expensive. The achiral method allows for determination of both enantiomers in 10 minutes, using relatively inexpensive instrumentation, although limits of detection suffer as a result. The shorter run time lends the advantage, however, of being more environmentally viable with less solvent waste.

  1. Conflict of interest: Authors declare no conflict of interest.

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Received: 2018-09-25
Accepted: 2019-03-30
Published Online: 2019-06-12

© 2019 M.M. López Guerrero et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 Public License.

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https://doi.org/10.1515/chem-2019-0049
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Separation; Enantiomer; Chiral; Achiral; HPLC
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Artikel in diesem Heft

  1. Regular Articles
  2. Research on correlation of compositions with oestrogenic activity of Cistanche based on LC/Q-TOF-MS/MS technology
  3. Efficacy of Pyrus elaeagnifolia subsp. elaeagnifolia in acetic acid–induced colitis model
  4. Anti-inflammatory and antinociceptive features of Bryonia alba L.: As a possible alternative in treating rheumatism
  5. High efficiency liposome fusion induced by reducing undesired membrane peptides interaction
  6. Prediction of the Blood-Brain Barrier Permeability Using RP-18 Thin Layer Chromatography
  7. Phytic Acid Extracted from Rice Bran as a Growth Promoter for Euglena gracilis
  8. Development of a validated spectrofluorimetric method for assay of sotalol hydrochloride in tablets and human plasma: application for stability-indicating studies
  9. Topological Indices of Hyaluronic Acid-Paclitaxel Conjugates’ Molecular Structure in Cancer Treatment
  10. Thermodynamic properties of the bubble growth process in a pool boiling of water-ethanol mixture two-component system
  11. Critical Roles of the PI3K-Akt-mTOR Signaling Pathway in Apoptosis and Autophagy of Astrocytes Induced by Methamphetamine
  12. Characteristics of Stable Hydrogen and Oxygen Isotopes of Soil Moisture under Different Land Use in Dry Hot Valley of Yuanmou
  13. Specific, highly sensitive and simple spectrofluorimetric method for quantification of daclatasvir in HCV human plasma patients and in tablets dosage form
  14. Chromium-modified cobalt molybdenum nitrides as catalysts for ammonia synthesis
  15. Langerhans cell-like dendritic cells treated with ginsenoside Rh2 regulate the differentiation of Th1 and Th2 cells in vivo
  16. Identification of Powdery Mildew Blumeria graminis f. sp. tritici Resistance Genes in Selected Wheat Varieties and Development of Multiplex PCR
  17. Computational Analysis of new Degree-based descriptors of oxide networks
  18. The Use Of Chemical Composition And Additives To Classify Petrol And Diesel Using Gas Chromatography–Mass Spectrometry And Chemometric Analysis: A Uk Study
  19. Minimal Energy Tree with 4 Branched Vertices
  20. Jatropha seed oil derived poly(esteramide-urethane)/ fumed silica nanocomposite coatings for corrosion protection
  21. Calculating topological indices of certain OTIS interconnection networks
  22. Energy storage analysis of R125 in UIO-66 and MOF-5 nanoparticles: A molecular simulation study
  23. Velvet Antler compounds targeting major cell signaling pathways in osteosarcoma - a new insight into mediating the process of invasion and metastasis in OS
  24. Effects of Azadirachta Indica Leaf Extract, Capping Agents, on the Synthesis of Pure And Cu Doped ZnO-Nanoparticles: A Green Approach and Microbial Activity
  25. Aqueous Micro-hydration of Na+(H2O)n=1-7 Clusters: DFT Study
  26. A proposed image-based detection of methamidophos pesticide using peroxyoxalate chemiluminescence system
  27. Phytochemical screening and estrogenic activity of total glycosides of Cistanche deserticola
  28. Biological evaluation of a series of benzothiazole derivatives as mosquitocidal agents
  29. Chemical pretreatments of Trapa bispinosa's peel (TBP) biosorbent to enhance adsorption capacity for Pb(ll)
  30. Dynamic Changes in MMP1 and TIMP1 in the Antifibrotic Process of Dahuang Zhechong Pill in Rats with Liver Fibrosis
  31. The Optimization and Production of Ginkgolide B Lipid Microemulsion
  32. Photodynamic Therapy Enhanced the Antitumor Effects of Berberine on HeLa Cells
  33. Chiral and Achiral Enantiomeric Separation of (±)-Alprenolol
  34. Correlation of Water Fluoride with Body Fluids, Dental Fluorosis and FT4, FT3 –TSH Disruption among Children in an Endemic Fluorosis area in Pakistan
  35. A one-step incubation ELISA kit for rapid determination of dibutyl phthalate in water, beverage and liquor
  36. Free Radical Scavenging Activity of Essential Oil of Eugenia caryophylata from Amboina Island and Derivatives of Eugenol
  37. Effects of Blue and Red Light On Growth And Nitrate Metabolism In Pakchoi
  38. miRNA-199a-5p functions as a tumor suppressor in prolactinomas
  39. Solar photodegradation of carbamazepine from aqueous solutions using a compound parabolic concentrator equipped with a sun tracking system
  40. Influence of sub-inhibitory concentration of selected plant essential oils on the physical and biochemical properties of Pseudomonas orientalis
  41. Preparation and spectroscopic studies of Fe(II), Ru(II), Pd(II) and Zn(II) complexes of Schiff base containing terephthalaldehyde and their transfer hydrogenation and Suzuki-Miyaura coupling reaction
  42. Complex formation in a liquid-liquid extraction-chromogenic system for vanadium(IV)
  43. Synthesis, characterization (IR, 1H, 13C & 31P NMR), fungicidal, herbicidal and molecular docking evaluation of steroid phosphorus compounds
  44. Analysis and Biological Evaluation of Arisaema Amuremse Maxim Essential Oil
  45. A preliminary assessment of potential ecological risk and soil contamination by heavy metals around a cement factory, western Saudi Arabia
  46. Anti- inflammatory effect of Prunus tomentosa Thunb total flavones in LPS-induced RAW264.7 cells
  47. Collaborative Influence of Elevated CO2 Concentration and High Temperature on Potato Biomass Accumulation and Characteristics
  48. Methods of extraction, physicochemical properties of alginates and their applications in biomedical field – a review
  49. Characteristics of liposomes derived from egg yolk
  50. Preparation of ternary ZnO/Ag/cellulose and its enhanced photocatalytic degradation property on phenol and benzene in VOCs
  51. Influence of Human Serum Albumin Glycation on the Binding Affinities for Natural Flavonoids
  52. Synthesis and antioxidant activity of 2-methylthio-pyrido[3,2-e][1,2,4] triazolo[1,5-a]pyrimidines
  53. Comparative study on the antioxidant activities of ten common flower teas from China
  54. Molecular Properties of Symmetrical Networks Using Topological Polynomials
  55. Synthesis of Co3O4 Nano Aggregates by Co-precipitation Method and its Catalytic and Fuel Additive Applications
  56. Phytochemical analysis, Antioxidant and Antiprotoscolices potential of ethanol extracts of selected plants species against Echinococcus granulosus: In-vitro study
  57. Silver nanoparticles enhanced fluorescence for sensitive determination of fluoroquinolones in water solutions
  58. Simultaneous Quantification of the New Psychoactive Substances 3-FMC, 3-FPM, 4-CEC, and 4-BMC in Human Blood using GC-MS
  59. Biodiesel Production by Lipids From Indonesian strain of Microalgae Chlorella vulgaris
  60. Miscibility studies of polystyrene/polyvinyl chloride blend in presence of organoclay
  61. Antibacterial Activities of Transition Metal complexes of Mesocyclic Amidine 1,4-diazacycloheptane (DACH)
  62. Novel 1,8-Naphthyridine Derivatives: Design, Synthesis and in vitro screening of their cytotoxic activity against MCF7 cell line
  63. Investigation of Stress Corrosion Cracking Behaviour of Mg-Al-Zn Alloys in Different pH Environments by SSRT Method
  64. Various Combinations of Flame Retardants for Poly (vinyl chloride)
  65. Phenolic compounds and biological activities of rye (Secale cereale L.) grains
  66. Oxidative degradation of gentamicin present in water by an electro-Fenton process and biodegradability improvement
  67. Optimizing Suitable Conditions for the Removal of Ammonium Nitrogen by a Microbe Isolated from Chicken Manure
  68. Anti-inflammatory, antipyretic, analgesic, and antioxidant activities of Haloxylon salicornicum aqueous fraction
  69. The anti-corrosion behaviour of Satureja montana L. extract on iron in NaCl solution
  70. Interleukin-4, hemopexin, and lipoprotein-associated phospholipase A2 are significantly increased in patients with unstable carotid plaque
  71. A comparative study of the crystal structures of 2-(4-(2-(4-(3-chlorophenyl)pipera -zinyl)ethyl) benzyl)isoindoline-1,3-dione by synchrotron radiation X-ray powder diffraction and single-crystal X-ray diffraction
  72. Conceptual DFT as a Novel Chemoinformatics Tool for Studying the Chemical Reactivity Properties of the Amatoxin Family of Fungal Peptides
  73. Occurrence of Aflatoxin M1 in Milk-based Mithae samples from Pakistan
  74. Kinetics of Iron Removal From Ti-Extraction Blast Furnace Slag by Chlorination Calcination
  75. Increasing the activity of DNAzyme based on the telomeric sequence: 2’-OMe-RNA and LNA modifications
  76. Exploring the optoelectronic properties of a chromene-appended pyrimidone derivative for photovoltaic applications
  77. Effect of He Qi San on DNA Methylation in Type 2 Diabetes Mellitus Patients with Phlegm-blood Stasis Syndrome
  78. Cyclodextrin potentiometric sensors based on selective recognition sites for procainamide: Comparative and theoretical study
  79. Greener synthesis of dimethyl carbonate from carbon dioxide and methanol using a tunable ionic liquid catalyst
  80. Nonisothermal Cold Crystallization Kinetics of Poly(lactic acid)/Bacterial Poly(hydroxyoctanoate) (PHO)/Talc
  81. Enhanced adsorption of sulfonamide antibiotics in water by modified biochar derived from bagasse
  82. Study on the Mechanism of Shugan Xiaozhi Fang on Cells with Non-alcoholic Fatty Liver Disease
  83. Comparative Effects of Salt and Alkali Stress on Antioxidant System in Cotton (Gossypium Hirsutum L.) Leaves
  84. Optimization of chromatographic systems for analysis of selected psychotropic drugs and their metabolites in serum and saliva by HPLC in order to monitor therapeutic drugs
  85. Electrocatalytic Properties of Ni-Doped BaFe12O19 for Oxygen Evolution in Alkaline Solution
  86. Study on the removal of high contents of ammonium from piggery wastewater by clinoptilolite and the corresponding mechanisms
  87. Phytochemistry and toxicological assessment of Bryonia dioica roots used in north-African alternative medicine
  88. The essential oil composition of selected Hemerocallis cultivars and their biological activity
  89. Mechanical Properties of Carbon Fiber Reinforced Nanocrystalline Nickel Composite Electroforming Deposit
  90. Anti-c-myc efficacy block EGFL7 induced prolactinoma tumorigenesis
  91. Topical Issue on Applications of Mathematics in Chemistry
  92. Zagreb Connection Number Index of Nanotubes and Regular Hexagonal Lattice
  93. The Sanskruti index of trees and unicyclic graphs
  94. Valency-based molecular descriptors of Bakelite network BNmn
  95. Computing Topological Indices for Para-Line Graphs of Anthracene
  96. Zagreb Polynomials and redefined Zagreb indices of Dendrimers and Polyomino Chains
  97. Topological Descriptor of 2-Dimensional Silicon Carbons and Their Applications
  98. Topological invariants for the line graphs of some classes of graphs
  99. Words for maximal Subgroups of Fi24‘
  100. Generators of Maximal Subgroups of Harada-Norton and some Linear Groups
  101. Special Issue on POKOCHA 2018
  102. Influence of Production Parameters on the Content of Polyphenolic Compounds in Extruded Porridge Enriched with Chokeberry Fruit (Aronia melanocarpa (Michx.) Elliott)
  103. Effects of Supercritical Carbon Dioxide Extraction (SC-CO2) on the content of tiliroside in the extracts from Tilia L. flowers
  104. Impact of xanthan gum addition on phenolic acids composition and selected properties of new gluten-free maize-field bean pasta
  105. Impact of storage temperature and time on Moldavian dragonhead oil – spectroscopic and chemometric analysis
  106. The effect of selected substances on the stability of standard solutions in voltammetric analysis of ascorbic acid in fruit juices
  107. Determination of the content of Pb, Cd, Cu, Zn in dairy products from various regions of Poland
  108. Special Issue on IC3PE 2018 Conference
  109. The Photocatalytic Activity of Zns-TiO2 on a Carbon Fiber Prepared by Chemical Bath Deposition
  110. N-octyl chitosan derivatives as amphiphilic carrier agents for herbicide formulations
  111. Kinetics and Mechanistic Study of Hydrolysis of Adenosine Monophosphate Disodium Salt (AMPNa2) in Acidic and Alkaline Media
  112. Antimalarial Activity of Andrographis Paniculata Ness‘s N-hexane Extract and Its Major Compounds
  113. Special Issue on ABB2018 Conference
  114. Special Issue on ICCESEN 2017
  115. Theoretical Diagnostics of Second and Third-order Hyperpolarizabilities of Several Acid Derivatives
  116. Determination of Gamma Rays Efficiency Against Rhizoctonia solani in Potatoes
  117. Studies On Compatibilization Of Recycled Polyethylene/Thermoplastic Starch Blends By Using Different Compatibilizer
  118. Liquid−Liquid Extraction of Linalool from Methyl Eugenol with 1-Ethyl-3-methylimidazolium Hydrogen Sulfate [EMIM][HSO4] Ionic Liquid
  119. Synthesis of Graphene Oxide Through Ultrasonic Assisted Electrochemical Exfoliation
  120. Special Issue on ISCMP 2018
  121. Synthesis and antiproliferative evaluation of some 1,4-naphthoquinone derivatives against human cervical cancer cells
  122. The influence of the grafted aryl groups on the solvation properties of the graphyne and graphdiyne - a MD study
  123. Electrochemical modification of platinum and glassy carbon surfaces with pyridine layers and their use as complexing agents for copper (II) ions
  124. Effect of Electrospinning Process on Total Antioxidant Activity of Electrospun Nanofibers Containing Grape Seed Extract
  125. Effect Of Thermal Treatment Of Trepel At Temperature Range 800-1200˚C
  126. Topical Issue on Agriculture
  127. The effect of Cladophora glomerata exudates on the amino acid composition of Cladophora fracta and Rhizoclonium sp.
  128. Influence of the Static Magnetic Field and Algal Extract on the Germination of Soybean Seeds
  129. The use of UV-induced fluorescence for the assessment of homogeneity of granular mixtures
  130. The use of microorganisms as bio-fertilizers in the cultivation of white lupine
  131. Lyophilized apples on flax oil and ethyl esters of flax oil - stability and antioxidant evaluation
  132. Production of phosphorus biofertilizer based on the renewable materials in large laboratory scale
  133. Human health risk assessment of potential toxic elements in paddy soil and rice (Oryza sativa) from Ugbawka fields, Enugu, Nigeria
  134. Recovery of phosphates(V) from wastewaters of different chemical composition
  135. Special Issue on the 4th Green Chemistry 2018
  136. Dead zone for hydrogenation of propylene reaction carried out on commercial catalyst pellets
  137. Improved thermally stable oligoetherols from 6-aminouracil, ethylene carbonate and boric acid
  138. The role of a chemical loop in removal of hazardous contaminants from coke oven wastewater during its treatment
  139. Combating paraben pollution in surface waters with a variety of photocatalyzed systems: Looking for the most efficient technology
  140. Special Issue on Chemistry Today for Tomorrow 2019
  141. Applying Discriminant and Cluster Analyses to Separate Allergenic from Non-allergenic Proteins
  142. Chemometric Expertise Of Clinical Monitoring Data Of Prolactinoma Patients
  143. Chemomertic Risk Assessment of Soil Pollution
  144. New composite sorbent for speciation analysis of soluble chromium in textiles
  145. Photocatalytic activity of NiFe2O4 and Zn0.5Ni0.5Fe2O4 modified by Eu(III) and Tb(III) for decomposition of Malachite Green
  146. Photophysical and antibacterial activity of light-activated quaternary eosin Y
  147. Spectral properties and biological activity of La(III) and Nd(III) Monensinates
  148. Special Issue on Monitoring, Risk Assessment and Sustainable Management for the Exposure to Environmental Toxins
  149. Soil organic carbon mineralization in relation to microbial dynamics in subtropical red soils dominated by differently sized aggregates
  150. A potential reusable fluorescent aptasensor based on magnetic nanoparticles for ochratoxin A analysis
  151. Special Issue on 13th JCC 2018
  152. Fluorescence study of 5-nitroisatin Schiff base immobilized on SBA-15 for sensing Fe3+
  153. Thermal and Morphology Properties of Cellulose Nanofiber from TEMPO-oxidized Lower part of Empty Fruit Bunches (LEFB)
  154. Encapsulation of Vitamin C in Sesame Liposomes: Computational and Experimental Studies
  155. A comparative study of the utilization of synthetic foaming agent and aluminum powder as pore-forming agents in lightweight geopolymer synthesis
  156. Synthesis of high surface area mesoporous silica SBA-15 by adjusting hydrothermal treatment time and the amount of polyvinyl alcohol
  157. Review of large-pore mesostructured cellular foam (MCF) silica and its applications
  158. Ion Exchange of Benzoate in Ni-Al-Benzoate Layered Double Hydroxide by Amoxicillin
  159. Synthesis And Characterization Of CoMo/Mordenite Catalyst For Hydrotreatment Of Lignin Compound Models
  160. Production of Biodiesel from Nyamplung (Calophyllum inophyllum L.) using Microwave with CaO Catalyst from Eggshell Waste: Optimization of Transesterification Process Parameters
  161. The Study of the Optical Properties of C60 Fullerene in Different Organic Solvents
  162. Composite Material Consisting of HKUST-1 and Indonesian Activated Natural Zeolite and its Application in CO2 Capture
  163. Topical Issue on Environmental Chemistry
  164. Ionic liquids modified cobalt/ZSM-5 as a highly efficient catalyst for enhancing the selectivity towards KA oil in the aerobic oxidation of cyclohexane
  165. Application of Thermal Resistant Gemini Surfactants in Highly Thixotropic Water-in-oil Drilling Fluid System
  166. Screening Study on Rheological Behavior and Phase Transition Point of Polymer-containing Fluids produced under the Oil Freezing Point Temperature
  167. The Chemical Softening Effect and Mechanism of Low Rank Coal Soaked in Alkaline Solution
  168. The Influence Of NO/O2 On The NOx Storage Properties Over A Pt-Ba-Ce/γ-Al2O3 Catalyst
  169. Special Issue on the International conference CosCI 2018
  170. Design of SiO2/TiO2 that Synergistically Increases The Hydrophobicity of Methyltrimethoxysilane Coated Glass
  171. Antidiabetes and Antioxidant agents from Clausena excavata root as medicinal plant of Myanmar
  172. Development of a Gold Immunochromatographic Assay Method Using Candida Biofilm Antigen as a Bioreceptor for Candidiasis in Rats
  173. Special Issue on Applied Biochemistry and Biotechnology 2019
  174. Adsorption of copper ions on Magnolia officinalis residues after solid-phase fermentation with Phanerochaete chrysosporium
  175. Erratum
  176. Erratum to: Sand Dune Characterization For Preparing Metallurgical Grade Silicon
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Heruntergeladen am 9.9.2025 von https://www.degruyterbrill.com/document/doi/10.1515/chem-2019-0049/html
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