Capillary zone electrophoresis of orotic acid in urine with on-line isotachophoresis sample pretreatment and diode array detection

Potentialities of capillary zone electrophoresis with on-line isotachophore sis sample pretreatment and diode array detection (ITP-CZE-DAD) to the sepa ration, detection and identification of trace analytes present in biologica l matrices were investigated. Urine represented a multicomponent, variable and high ionic strength matrix while erotic acid was chosen as a model anal yte of a practical clinical relevance in this investigation. Using the ITP- CZE combination in the column-coupling configuration of the. separation sys tem ITP provided an enhanced sample load capacity to the separation system (a 30 mul sample injection volume), concentrated the analyte and served as an on-line sample clean up technique. On the other hand, CZE performed a fi nal separation of the analyte from matrix constituents present in the ITP p retreated sample and provided favorable conditions for its detection and id entification by DAD. using current correction and smoothing procedures anal ytically relevant DAD spectra of erotic acid could be obtained also in inst ances when this was injected in a model sample at a 2 . 10(-7) mol/l concen tration (an estimated limit of determination of erotic acid at a 218 mm det ection wavelength). ITP-CZE separations of urine samples (based on differen ces in acid-base properties and host-guest complexations of the analyte and matrix anionic constituents) led to significant sample clean ups. Conseque ntly, DAD spectra of erotic acid matching its reference spectrum, could be acquired also in instances when the acid was present in urine matrices (loa ded in 30 mul injection volumes of 20-fold diluted urine samples) at 4-6 . 10(-7) mol/l concentrations. Here, residual trace matrix interferents preve nted a closer approach to the above value attainable for model samples. Alt hough this work was focused only on one analyte: and urine matrix it implie s very promising potentialities of the ITP-CZE-DAD combination in the ident ification and quantitation of trace analytes present in biological matrices , in general. (C) 2001 Elsevier Science BN. All rights reserved.