A flow-through solid phase UV spectrophotometric biparameter sensor for the sequential determination of ascorbic acid and paracetamol

For the first time, a continuous flow system with solid phase UV spectropho tometric detection (an optosensor) is described for the sequential determin ation of two analytes based on the alternate use of two carrier/self-elutin g agents. The selective and sequential sorption of both on an active solid support (an anion exchanger gel placed in the detection zone into an approp riate quartz flow cell) is performed and their respective UV intrinsic abso rbances monitored. Each carrier itself elutes the respective analyte from t he solid support, so regenerating the sensing zone. Ascorbic acid and paracetamol in concentrations ranging from 0.3 to 20 mu g ml(-1) and from 0.4 to 25 mu g ml(-1), respectively, could be determined w ith this UV flow-through optosensor using sodium acetate/acetic acid (pH 5. 6) and 0.05 M NaCl (pH 12.5), respectively as carrier/self-eluting solution s and Sephadex QAE A-25 anion exchanger gel as solid phase placed in the in ner of an 1 mm optical path length quartz flow cell. The RSDs % (n = 10) we re lower than 1.3 (for ascorbic acid) and than 1.5 (for paracetamol). Detec tion limits (criterion 3 sigma) as low as 0.02 mu g ml(-1) were achieved in both cases. Application to the analysis of pharmaceutical samples (in addition to synth etic ones) testifies the utility of this sequential sensor, which tolerates amounts of the species usually accompanying the analytes much higher than those ones found in these samples. (C)2000 Elsevier Science B.V. All rights reserved.