Pl. Desbene et al., UTILIZATION OF FLUORESCEIN SODIUM-SALT IN LASER-INDUCED INDIRECT FLUOROMETRIC DETECTION OF IONS SEPARATED BY CAPILLARY ZONE ELECTROPHORESIS, Journal of chromatography, 689(1), 1995, pp. 135-148
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+).