Abstract: Continuous-flow and static dialysis coupled on-line to liquid chromatography was evaluated and an automated method for determination of ciprofloxacin in biological samples developed. A trace enrichment column packed with C18 material and coupled with a continuous dialysis and reversed-phase HPLC system with fluorescence detection enabled determination of ciprofloxacin in human blood serum at the 0.1-nmol/l level. The amount of analyte pre-concentrated and loaded on the HPLC system was linearly proportional to the concentration in the dialysed sample over more than 4 orders of magnitude (up to 1.10-6 M). Data for linearity, repeatability and detectability for each particular set-up are given. The trace enrichment step eliminates band broadening caused by solvents different from those of the eluent and affecting retention of ciprofloxacin on the analytical column (increase in k) due to the on-column change of eluent composition. In analysis of human serum samples phthalates leached from plastic materials may interfere due to coelution with the analyte.

Abstract: The effect of fluoride ions on the electrochemical behavior of a zirconium metal electrode was investigated. Since zirconium metal is always covered by a layer of oxide, the anodic characteristic of a Zr/ZrO2 electrode depends highly on the electrolyte composition. Only in hydrochloric and perchloric acid media was a direct proportionality between fluoride concentration and anodic current density found. In other electrolytes the fluoride ion-induced dissolution of the zirconium metal leads to an increase in ZrO2 film thickness, and as a consequence, the mass transport of fluoride through the oxide layer is hindered. The mechanism of the zirconium electrode dissolution at low concentrations of fluoride (below 1 x 10^-3 M) seems to be different from that at high concentrations. The dependence of the equilibrium potential on the fluoride concentration is far from the Nernstian one, and a zirconium electrode could be successfully applied in the potentiometric mode of operation only as an indicator electrode in titrations. The proportionality between the anodic current density and the fluoride ion concentration in perchloric acid media could be exploited for the amperometric detection of fluoride. With a thin-layer cell and a zirconium metal based indicator electrode, nanogram amounts of fluoride could be detected by a simple flow injection system.