Coupled Systems Involving Capillary Electrophoresis

Electropherograms of a urine sample (8 ml) spiked with non-steroidal anti-inflammatory drugs (10 p-g/ml each) after direct CE analysis (b) and at-line SPE-CE (c). Peak identification is as follows I, ibuprofen N, naproxen K, ketoprofen P, flurbiprofen. Reprinted from Journal of Chromatography, 6 719, J. R. Veraait et al., At-line solid-phase exti action for capillary electrophoresis application to negatively charged solutes, pp. 199-208, copyright 1998, with permission from Elsevier Science. 

The use of SPME for CE has not (yet) been studied widely. Li and Weber (170) reported an off-line SPME-CE approach for the determination of barbiturates in urine and serum, utilizing a sorbent of plasticized PVC coated around a stainless steel rod. Eor extraction, the coated rod was inserted for 4 min in a Teflon tube containing 50 p.1 of sample, and next the rod was repeatedly desorbed in another Teflon tube which each time contained 5 p.1 of desorption solution. This solution was transferred to an injection vial and an aliquot was injected into the CE system (Eigure 11.19). The extraction procedure appeared to be selective and effectively allowed the handling of very small samples. 

Analogous to two-dimensional LC, the on-line coupling of LC and CE has been carried out both in the heart-cut and the comprehensive mode. In a heart-cut LC-CE study, a protein G immunoaffinity LC column was used to selectively preconcentrate insulin from serum (171). A 1 p.1 elution plug comprising the insulin was switched on-line to the CE system where a part was injected into the capillary for final separation. With CE, efficient separations can be obtained in a 

Hennion, Solid-phase exti action method development, sorbents and coupling with liquid cliromatography , J. Chromatogr. A 856 3-54 (1999). 

R Regnier and G. Huang, Future potential of targeted component analysis by multidimensional liquid cliromatography-mass spectrometry , J. Chromatogr. A 750 3-10 (1996). 

Opiteck, J. W. Jorgenson, M. A. Moseley III and R. J. Anderegg, Two-dimensional microcolumn HPLC coupled to a single-quadrupole mass spectrometer for the elucidation of sequence tags and peptide mapping , J. Microcolumn Sep. 10 365-375 (1998). 

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Chromatographic and electrophoretic separations are truly orthogonal, which makes them excellent techniques to couple in a multidimensional system. Capillary electrophoresis separates analytes based on differences in the electrophoretic mobilities of analytes, while chromatographic separations discriminate based on differences in partition function, adsorption, or other properties unrelated to charge (with some clear exceptions). Typically in multidimensional techniques, the more orthogonal two methods are, then the more difficult it is to interface them. Microscale liquid chromatography (p.LC) has been comparatively easy to couple to capillary electrophoresis due to the fact that both techniques involve narrow-bore columns and liquid-phase eluents. 

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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