IMPROVED PHOTOMETRIC DETECTION OF METAL-IONS BY CAPILLARY-ZONE-ELECTROPHORESIS AFTER PRECAPILLARY COMPLEXATION

Precapillary reactions using complexing reagents are increasingly bein g used to carry out separations of metal ions by capillary zone electr ophoresis. To compensate for the sensitivity limitations of on-column photometric detection, several approaches were evaluated. Parameters a ffecting the sensitivity response of a direct detection system, such a s the detection wavelength, sample size, applied voltage, and electrol yte concentration, were examined to produce the best possible sensitiv ity for metal ions complexed with cyclohexane-1,2-diaminetetraacetic a cid. Using injection in the electrokinetic mode, a 2-fold increase in detectability over hydrodynamic (gravity) injection was obtained for c ertain metal analytes that corresponds to the detection limits in the sub-mu g/l range. A characterization and optimization of photometric d etection in an indirect format have been conducted. An organic dye, co mbined with the carrier electrolyte to impart an absorbance background in the visible range and selected with due account for its spectral a nd electrophoretic characteristics, was found to provide micromolar-le vel sensitivities. Feasibility of on-line (stacking) sample concentrat ion for metal complexes has also been demonstrated. (C) 1998 Elsevier Science B.V. All rights reserved.