MULTICOMMUTATION IN FLOW-ANALYSIS - PART-6 - BINARY SAMPLING FOR WIDECONCENTRATION RANGE TURBIDIMETRIC DETERMINATION OF SULFATE IN PLANT DIGESTS

An automatic continuous flow procedure for turbidimetric determination of sulphate in acidic digests of plant materials, employing a flow ne twork based on multicommutation and binary sampling is described. The method is based on the precipitation of sulphate anions with barium io ns followed by photometric monitoring of the resulting suspension. A s ingle pumping channel was used, handling both samples and reagents by means of computer-controlled three-way solenoid valves. In order to ex tend the determination concentration range up to 500 mg l(-1) SO42- wi thout any modification in the structure of the flow network two analyt ical curves are generated. The first curve comprized the concentration range from 10-150 mg l(-1) SO42- and the second one, that from 100-50 0 mg l(-1) SO42-. Results presented good agreement at the 95% confiden ce level with those obtained by the usual FIA system. Other relevant f eatures such as a throughput of 100 determinations per hour, a relativ e standard deviation of 2% (n=11) and a reagent consumption of 7 mg Ba Cl2.2H(2)O plus 1.5 mg EDTA per determination were also achieved. (C) 1998 Elsevier Science B.V.