ONLINE ISOTACHOPHORESIS-CAPILLARY ZONE ELECTROPHORESIS VERSUS SAMPLE SELF STACKING CAPILLARY ZONE ELECTROPHORESIS - ANALYSIS OF HIPPURATE IN SERUM

This paper is aimed at the problem of sensitive analysis of a microcom ponent in a sample with a bulk macrocomponent and complex matrix by ca pillary electrophoresis. In such samples, the simple way to increase t he sensitivity by increasing the injected sample volume is counterwork ed by the stacking-destacking processes due to the presence of transie nt isotachophoresis (ITP) and a certain maximum sample load exists whi ch gives useful results. The important analytical task of the analysis of hippuric acid (benzoyl glycine) was selected as the model problem. The aim was to reach the highest possible sensitivity in the analysis of hippuric acid in serum of healthy persons where hippuric acid repr esented a microcomponent and serum was a representative of a sample ma trix containing varying amounts of macrocomponents. In order to find t he maximum allowable sample load (volume) that enabled maximum sensiti vity, various stacking techniques in two types of instrumentation for capillary zone electrophoresis (CZE) and a commercially available inst rumentation for the on-line ITP-CZE combination were compared. The sys tems for CZE differed in detectors and in using an open or closed capi llary of different diameter and material, which resulted in different sensitivity of the analyses of model samples. In analyses of serum sam ples, however, comparable limits of detection were obtained using both a single ITP and CZE with the open or closed capillary (6.10(-5) M hi ppurate). A limit of detection two-orders of magnitude lower (7.10(-7) M hippurate) was reached in the instrumentation for the ITP-CZE combi nation even though the parameters of the capillary and the detector th at were available for the CZE step were substantially worse than those of the open CZE system that was used.