Flow-injection system with enzyme reactor for differential amperometric determination of hydrogen peroxide in rainwater

Differential determinations of hydrogen peroxide (H2O2) have been performed by amperometry, combining flow-injection analysis (FIA) and a tubular reactor containing immobilized enzymes. A gold microelectrode modified by electrochemical deposition of platinum was employed as working electrode. Hydrogen peroxide was quantified in rainwater using amperometric differential measurements at +0.60 V versus Ag/AgCl(sat). For the enzymatic consumption of H2O2, a tubular reactor containing immobilized catalase was constructed, using a novel way for immobilization of enzymes on Amberlite IRA-743 resin. The linear dynamic range in H2O2 extends from 1 to 100×10-6 mol/l, at pH 7.0. At flow rate of 2.0 ml/min and injecting 150 mul sample volumes, the sampling frequency of the 90 determinations/h is afforded. The reproducibility of the current peaks for hydrogen peroxide in 10-5 mol/l range concentration shown a R.S.D. better than 1%. The detection limit of the method is 2.9×10-7 mol/l (1.5 ng of H2O2 in a 150 mul sample). The rainwater samples analyses were compared with the parallel amperometric determinations using static mercury electrode and by spectrophotometry, showing very good correlation between the three methods.