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Biomedical and Pharmaceutical Applications                      289











































                           Figure 11.19 SPME–CE analysis of urine samples: (a) blank urine (a) directly injected and
                           extracted for (b) 5 (c) 10 and (d) 30 min; (b) Urine spiked with barbiturates, extracted for (e)
                           30 and (f, g) 5 min. Peak identification is as follows: 1, pentobartibal; 2, butabarbital; 3, seco-
                           barbital; 4, amobarbital; 5, aprobarbital; 6, mephobarbital; 7, butalbital; 8, thiopental.
                           Concentrations used are 0.15–1.0 ppm (e, f) and 0.05–0.3 ppm (g). Reprinted from
                           Analytical Chemistry, 69, S. Li and S. G. Weber, ‘Determination of barbiturates by solid-
                           phase microextraction and capillary electrophoresis,’ pp. 1217–1222, copyright 1997, with
                           permission from the American Chemical Society.


                           11.8.2  LC–CE

                           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  l 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
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