Monosegmented flow system exploiting multicommutation applied to spectrophotometric determination of manganese in soybean digests Original Research Article

A flow system combining binary sampling and monosegmented flow implemented by multicommutation was developed to improve sensitivity and sampling rate of spectrophotometric methods based on slow chemical reactions. The flow network was assembled from a set of computer controlled three-way solenoid valves. The spectrophotometric method was based on manganese (II) oxidation by periodate in phosphoric acid medium to form the permanganate anion. The reaction is relatively slow and at 47°C a sample residence time of ca. 5 min is necessary to attain equilibrium conditions. However, by exploiting binary sampling and monosegmented flow analysis, quantitative conversion with a sampling rate of 50 determinations per hour was achieved. The procedure was applied to Mn determination in soybean digests, showing as profitable features a linear response for sample concentrations ranging from 2.50 to 40.00 mg l−1 Mn2+, a relative standard deviation of 0.27% (n=9) for a sample solution containing 17.1 mg l−1 Mn2+, a low reagent consumption (30 mg NaIO4 per determination) and a detection limit of 1.2 mg l−1 (99.7% confidence level). Results agreed with those obtained by inductively coupled argon plasma atomic emission spectrometry at 95% confidence level.