Steady-state capillary electrophoresis

Isotachophoresis. In isotachophoresis (ITP), or displacement electrophoresis or multizonal electrophoresis, the sample is inserted between two different buffers (electrolytes) without electroosmotic flow. The electrolytes are chosen so that one (the leading electrolyte) has a higher mobility and the other (the trailing electrolyte) has a lower mobility than the sample ions. An electric field is applied and the ions start to migrate towards the anode (anions) or cathode (cations). The ions separate into zones (bands) determined by their mobilities, after which each band migrates at a steady-state velocity and steady-state stacking of bands is achieved. Note that in ITP, unlike ZE, there is no electroosmotic flow and cations and anions cannot be separated simultaneously. Reference 26 provides a recent example of capillary isotachophoresis/zone electrophoresis coupled with nanoflow ESI-MS. 

The most common classification scheme in electrophoresis focuses on the nature of electrolyte system. Using this scheme, electrophoretic modes are classified as continuous or discontinuous systems. Within these groupings the methods may be further divided on the basis of constancy of the electrolyte if the composition of the background electrolyte is constant as in capillary zone electrophoresis, the result is a kinetic process. If the composition of the electrolyte is not constant, as in isoelectric focusing, the result is a steady-state process. 

The concentration depends only on that of the leading ion it is independent of the initial concentration in the sample. Therefore, ITP can act as an enrichment method, analogous to displacement chromatography and in contrast to zone electrophoresis and elution chromatography. The concentration in the steady state is adjusted to the value given in Eq. (2). If the concentration of the analyte species is lower in the initial sample, the higher steady-state concentration is established. This concentration is independent of the migration distance there is no dilution with a BGE as there is in capillary zone electrophoresis (CZE). 

In capillary electrophoresis (CE), analytes are separated due to their different velocities under the influence of an electric field. The analytes reach a steady-state velocity that can be expressed independently of the field strength as the electrophoretic mobility (pe). 

Beckers, J.L., Steady-state models in electrophoresis From isotachophoresis to capillary zone electrophoresis. Electrophoresis, 16, 1987-1998, 1995. 

Thormann, W., Caslavska, J., and Mosher, R.A., Impactof electroosmosis on isotachophoresis in open-tubular fused-sUica capillaries Analysis of the evolution of a stationary steady-state zone structure by computer simulation and experimental validation. Electrophoresis, 16, 2016, 1995. 

However, the analytical techniques for thiamine and its phosphate esters seem to be in a steady state during the recent past for nearly 10 years. No marked developments in practical techniques and/or methodology in the theoretical basis for the analysis of thiamine and its phosphates have been reported. For example, mass spectrometry and capillary electrophoresis seem to increase in importance in the whole field of vitamin analysis other than thiamine. As described in the text, however, these techniques were applied only in a limited number of thiamine analyses. 

Results on the evaluation of the analytical and isotope ratio performance of ICP-TOF-MS measurements in steady-state signals"" " were discussed earlier in this chapter. However, the major application field of ICP-TOF-MS involves the multi-element and multiisotope analysis of rapid transient signals such as those commonly encountered in flow injection, 27,28,29-35 electrothermal vaporisation, laser ablation, "" capillary electrophoresis, (CE)" and chromatography.From the number of references related to the coupling of ICP-TOF-MS with a separation system, TOF-MS seems to be an attractive alternative to scanning-based systems for hyphenated speciation analysis. Leach et have recently reviewed the different hyphenated speciation systems that employ ICP-TOF-MS. 

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