flow injection spectrophotometric determination of sulphide by catalytic reduction of toluidine blue

sulphide was determined spectrophotometrically at 628 nm and ph 6.7 based on its catalytic reduction of toluidine blue in the presence of se(iv) using a flow injection system. after optimization of the measuring conditions the calibration curve was found linear up to 25 mg/ml and the detection limit was 0.3 mg/ml (30 ml injections). the relative standard deviation for the determination of 10 mg/ml sulphide was 1.2% (n=14). the injection rate was 30 h-1.