New Potentiometric Sensors for Picrate Determination Using Flow‐Through System: Application to Kinetic Assessment of Se(IV)

Abstract

AbstractTwo new selective and sensitive poly(vinyl chloride) membrane sensors are developed for measuring picrate ions based on the use of nitron picrate [(Nit)(Pic)] and iron(II)‐bathophenanthroline picrate [Fe(bphen)3)(Pic)2] ion pairs in plasticized poly(vinyl chloride) membrane. The sensors display Nernstian response with slopes of −57.2±0.8 and −58.8±0.5 mV decade−1 over the range of 3.0×10−5 to −1.0×10−2 and 4.6×10−6–1.0×10−2 mol L−1 and detection limits of 7.4×10−6 and 3.07×10−6 mol L−1 for [(Nit)(Pic)] and [Fe(bphen)3)(Pic)2] membrane‐based sensors, respectively. The sensors exhibit long life‐span, long term potential stability, high reproducibility, fast response and good discrimination ability towards picrate ions in comparison with many other anions. A tubular detector based on [Fe(bphen)3][Pic]2 was further developed and coupled to a flow‐injection system for picrate (Pic) determination. Under optimized conditions, the linearity range is 1.0×10−5–1.0×10−1 mol L−1, with a slope of −47.9±0.1 mV decade−1 and a reproducibility of ±0.3 mV (n=5). The sensor is utilized for a kinetic quantification of selenium in pharmaceutical preparations. The alkaline solution of picrate is allowed to react in a batch system with Na2S, in the presence of selenium(IV) as a catalyst. The changes in potential, resulting from the decrease of the picrate anions are monitored with the picrate sensor. The calibration curve of Se is linear in the concentration range 0.14–0.7 µg mL−1, with a lower limit of detection of 1.0 ng mL−1.