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

For the first time, a continuous flow system with solid phase UV spectrophotometric detection (an optosensor) is described for the sequential determination of two analytes based on the alternate use of two carrier/self-eluting agents. The selective and sequential sorption of both on an active solid support (an anion exchanger gel placed in the detection zone into an appropriate quartz flow cell) is performed and their respective UV intrinsic absorbances monitored. Each carrier itself elutes the respective analyte from the solid support, so regenerating the sensing zone. Ascorbic acid and paracetamol in concentrations ranging from 0.3 to 20 μg ml−1 and from 0.4 to 25 μg ml−1, respectively, could be determined with 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 solutions and Sephadex QAE A-25 anion exchanger gel as solid phase placed in the inner of an 1 mm optical path length quartz flow cell. The RSDs % (n = 10) were lower than 1.3 (for ascorbic acid) and than 1.5 (for paracetamol). Detection limits (criterion 3σ) as low as 0.02 μg ml−1 were achieved in both cases. Application to the analysis of pharmaceutical samples (in addition to synthetic 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.