MULTICOMMUTATION IN FLOW-ANALYSIS .2. BINARY SAMPLING FOR SPECTROPHOTOMETRIC DETERMINATION OF NICKEL, IRON AND CHROMIUM IN STEEL ALLOYS

Multicommutation now systems for the spectrophotometric determination of nickel, iron and chromium in acid solutions of steel alloys employing a binary sampling approach are described. Dimethylglyoxime, salicylic acid and diphenylcarbazide were used as chromogenic reagents for nickel, iron and chromium, respectively. The now networks were designed with active devices in order to provide facilities to handle reagent solutions employing a single pumping channel to propel all reagent solutions. Interference caused by iron on the nickel determination was suppressed on-line by using triethanolamine as masking agent. For sample concentrations ranging from 5 to 50 mg/l, the proposed method is characterized by a throughput of 60 determinations per hour and a relative standard deviation of about 1%. Consumptions of potassium peroxodisulphate and dimethylglyoxime solutions were 56 and 78 mu l per determination, respectively. Iron and chromium were determined sequentially, with a reagent consumption of 80 mu l and 26 mu l, respectively. For sample concentrations ranging from 25 to 200 mg/l Fe and 20 to 60 mg/l Cr a throughput of 130 determinations per hour was achieved. Results compared well with those obtained by inductively coupled argon plasma atomic emission spectrometry.