UTILIZATION OF FLUORESCEIN SODIUM-SALT IN LASER-INDUCED INDIRECT FLUOROMETRIC DETECTION OF IONS SEPARATED BY CAPILLARY ZONE ELECTROPHORESIS

Indirect detection, the principles of which were demonstrated some yea rs ago, has attracted renewed interest in both UV-visible and fluorime tric detection. This paper reports the implementation of laser-induced indirect fluorimetric detection using a commercially available detect or and its association with high-performance capillary electrophoresis for the determination of inorganic ions. In order to optimize the res ponse sensitivity, the fluorescent agent being fluorescein sodium salt , the influence of the fluorescein sodium salt concentration, the ioni c strength, the electrolyte pH and the gain on the signal-to-noise rat io were studied successively, the injection mode being either electrok inetic or hydrodynamic. In the case of a 75 mu m I.D. fused-silica cap illary, detection limits were in the ppb range or about 10 ppb for alk ali metal cations using injection in the electrokinetic or in the hydr odynamic mode, respectively. As the detection system used had its maxi mum sensitivity at basic pH, the use of a complexing agent was require d in order to perform the determination of alkaline earth metal cation s, because they precipitate or are adsorbed at basic pH. Therefore, us ing ethylenediaminetetraacetic acid sodium salt (EDTA), it is possible to analyse at pH 7.5, in less than 5 min, a mixture containing three alkaline earth metal cations (Ba2+, Ca2+ and Mg2+) and three transitio n metals cations (Fe3+, Zn2+ and Cu2+) in addition to the previously m entioned alkali metal cations (Li+ and K+).