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8. Capillary Electrophoresis (CE)

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Organic Trace Analysis
This chapter is in the book Organic Trace Analysis
8 Capillary Electrophoresis (CE)8.1 General RemarksIn capillary electrophoresis (CE), an electric field is used to separate components ofa mixture dissolved in an electrolytic buffer solvent which is flowing through a nar-row tube, a capillary of sub-mm diameter, typically 25–75,m. When an electrical fieldis applied, charged molecules, cations and anions move toward the electrode of op-posing charge, that is, cations toward the cathode and anions toward the anode. InCE, even uncharged molecules can be analyzed due to the electroosmotic flow of thebuffer system (see below).Many types of CE have been developed which will briefly be described in thefollowing: capillary zone electrophoresis (CZE), capillary gel electrophoresis (CGE),capillary isoelectric focusing (CIEF), capillary isotachophoresis (CITP) and micellarelectrokinetic chromatography.The advantage of using capillaries in electrophoretic separations is that high elec-tric voltages (10–30 kV) and electrical fields (100–500 V/cm) can be applied with onlylittle heat generation because the high resistance of the capillary limits the currentgeneration; in addition, the large surface-to-volume ratio of the capillary efficientlyhelps dissipating the generated heat. Such high electrical fields lead to short analysistimes. The high resolution in CE separations with typically more than 105theoreticalplates is due in part to the electroosmotic plug flow (see below) which also enables thesimultaneous analysis of all charged and uncharged solutes. Only small amounts ofsamples are needed for CE (1–50 nL), but with high enough concentrations dependingon the detection method applied which will be presented below. CE can be applied forseparations of all kind of analytes, such as amino acids, drugs, vitamins, pesticides,inorganic ions, organic acids, dyes, surfactants, peptides and proteins, carbohydratesand oligonucleotides.8.2 Working Principles8.2.1 Interaction of Charged Analyte Species with an External Electric FieldIn CE, analytes move through electrolyte solutions under the influence of an electricfield. A basic scheme of a CE system is shown in Figure 8.1.The ends of a narrow-fused silica capillary are placed in buffer reservoirs whichcontain the electrodes providing the electrical contact between a high-voltage powersupply and the capillary. The sample is loaded onto the capillary by replacing one ofthe reservoirs (usually at the anode) with the sample reservoir and applying eitheran electric field or an external pressure. After replacing the buffer reservoir, theelectric field is applied and separation starts. Optical detection can be made at theDOI 10.1515/9783110441154-008
© 2017 Walter de Gruyter GmbH, Berlin/Munich/Boston

8 Capillary Electrophoresis (CE)8.1 General RemarksIn capillary electrophoresis (CE), an electric field is used to separate components ofa mixture dissolved in an electrolytic buffer solvent which is flowing through a nar-row tube, a capillary of sub-mm diameter, typically 25–75,m. When an electrical fieldis applied, charged molecules, cations and anions move toward the electrode of op-posing charge, that is, cations toward the cathode and anions toward the anode. InCE, even uncharged molecules can be analyzed due to the electroosmotic flow of thebuffer system (see below).Many types of CE have been developed which will briefly be described in thefollowing: capillary zone electrophoresis (CZE), capillary gel electrophoresis (CGE),capillary isoelectric focusing (CIEF), capillary isotachophoresis (CITP) and micellarelectrokinetic chromatography.The advantage of using capillaries in electrophoretic separations is that high elec-tric voltages (10–30 kV) and electrical fields (100–500 V/cm) can be applied with onlylittle heat generation because the high resistance of the capillary limits the currentgeneration; in addition, the large surface-to-volume ratio of the capillary efficientlyhelps dissipating the generated heat. Such high electrical fields lead to short analysistimes. The high resolution in CE separations with typically more than 105theoreticalplates is due in part to the electroosmotic plug flow (see below) which also enables thesimultaneous analysis of all charged and uncharged solutes. Only small amounts ofsamples are needed for CE (1–50 nL), but with high enough concentrations dependingon the detection method applied which will be presented below. CE can be applied forseparations of all kind of analytes, such as amino acids, drugs, vitamins, pesticides,inorganic ions, organic acids, dyes, surfactants, peptides and proteins, carbohydratesand oligonucleotides.8.2 Working Principles8.2.1 Interaction of Charged Analyte Species with an External Electric FieldIn CE, analytes move through electrolyte solutions under the influence of an electricfield. A basic scheme of a CE system is shown in Figure 8.1.The ends of a narrow-fused silica capillary are placed in buffer reservoirs whichcontain the electrodes providing the electrical contact between a high-voltage powersupply and the capillary. The sample is loaded onto the capillary by replacing one ofthe reservoirs (usually at the anode) with the sample reservoir and applying eitheran electric field or an external pressure. After replacing the buffer reservoir, theelectric field is applied and separation starts. Optical detection can be made at theDOI 10.1515/9783110441154-008
© 2017 Walter de Gruyter GmbH, Berlin/Munich/Boston

Chapters in this book

  1. Frontmatter I
  2. Preface V
  3. Contents VII
  4. 1. Overview 1
  5. 2. Statistical Evaluation 10
  6. 3. Quality Control Strategies 19
  7. 4. Sampling of Organic Trace Contaminants 33
  8. 5. Sample Treatment Before Analysis 76
  9. 6. Enrichment and Sample Cleanup 79
  10. 7. Chromatography 129
  11. 8. Capillary Electrophoresis (CE) 208
  12. 9. Mass Spectrometry 229
  13. 10. Receptor-based Bioanalysis for Mass Screening 250
  14. 11. Selected Applications 269
  15. List of Abbreviations 347
  16. Index 351
Readers are also interested in:
https://doi.org/10.1515/9783110441154-008

Chapters in this book

  1. Frontmatter I
  2. Preface V
  3. Contents VII
  4. 1. Overview 1
  5. 2. Statistical Evaluation 10
  6. 3. Quality Control Strategies 19
  7. 4. Sampling of Organic Trace Contaminants 33
  8. 5. Sample Treatment Before Analysis 76
  9. 6. Enrichment and Sample Cleanup 79
  10. 7. Chromatography 129
  11. 8. Capillary Electrophoresis (CE) 208
  12. 9. Mass Spectrometry 229
  13. 10. Receptor-based Bioanalysis for Mass Screening 250
  14. 11. Selected Applications 269
  15. List of Abbreviations 347
  16. Index 351
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