TRACE ANALYSIS OF PROTEINS BY CAPILLARY ZONE ELECTROPHORESIS WITH ON-COLUMN TRANSIENT ISOTACHOPHORETIC PRECONCENTRATION

The qualitative and quantitative aspects of transient isotachophoretic (ITP) sample preconcentration in the capillary zone electrophoretic a nalysis of protein samples have been demonstrated. By the proper selec tion of components of the background electrolyte and/or additives to t he sample solution, two basic electrolyte arrangements have been emplo yed. In the first, a typical isotachophoretic electrolyte system consi sting of a leading and terminating electrolyte was used, and after foc using and preconcentration, the terminating electrolyte was replaced b y the leading electrolyte, with the separation being continued in the zone electrophoretic mode. In the second, only one background electrol yte was used, containing a co-ion with low electrophoretic mobility, a nd the sample was supplemented with a salt of a highly mobile co-ion. In this case transient isotachophoretic migration of the sample ions t ook place at the beginning of the migration and gradually changed to t he zone electrophoretic mode. Sample mixtures containing basic (positi vely charged) or acidic (negatively charged) proteins were examined us ing surface-coated fused-silica capillaries. For acidic proteins, bare silica was also tested. The isotachophoretic sample stacking permitte d injection and preconcentration of sample volumes two to three orders of magnitude higher than usual in capillary zone electrophoresis. For example, up to 1 muL was injected into a 75 mum ID capillary. This ap proach afforded quantitative analysis of protein samples in the concen tration range of 10(-7)-10(-8) M, with detection limits of approximate ly 10(-9) M. Furthermore, with constant sample volume injected, good r eproducibility of migration times was obtained. Finally, the determina tion of trace components in the presence of a major sample component u sing transient ITP preconcentration has been demonstrated.