UTILIZATION OF FLUORESCEIN SODIUM-SALT IN LASER-INDUCED INDIRECT FLUOROMETRIC DETECTION .2. APPLICATION TO ORGANIC-ANIONS

Previously, we have used the fluorescein sodium salt to generate the background signal in the indirect fluorimetric detection of inorganic cations (alkaline; alkaline earth metals and transition metals) separated by capillary zone electrophoresis (CZE). In this work, we report that the use of fluorescein sodium salt can be extended to the detection of organic anions. A study of the detection thresholds and of reproducibility (elution times and effective electrophoretic mobilities) was performed. As samples we used, on the one hand, a mixture of n-alkane sulfonates (from C-1 to C-10) and, on the other hand, a mixture of carboxylic acids (from C-1 to C-18). Under the optimal conditions, detection thresholds of about 700 to 800 ppb were obtained and the reproducibility of effective electrophoretic mobilities was characterized by a relative standard deviation of about 0.5%. Calibration curves were also established (correlation coefficients were found to be between 0.995 and 0.9998). Finally, we compared the evolution of the experimental response coefficients of these two series of samples as a function of alkyl chain length with theoretical response coefficients obtained from findings reported by Ackermans et al. [J. Chromatogr., 549 (1991) 345].