SANDWICH TECHNIQUES IN FLOW-INJECTION ANALYSIS .3. SIMULTANEOUS DETERMINATION OF CR(VI) IN 2 CONCENTRATION RANGES

A flow-injection system based on the sandwich technique is proposed for the determination of Cr(VI). Two simultaneous working ranges of concentration are achieved by appropriate selection of the reagent composition at the two reagent-sample interfaces. The optimized system allows the determination of Cr(VI) at levels up to 1-mu-g ml-1 with a detection limit of 0.01-mu-g ml-1 for one of the interfaces. For the other, determinations up to 30-mu-g ml-1 with a detection limit of 0.5-mu-g ml-1 are possible. The sample throughput achieved was about 45 h-1 with a relative standard deviation < 1% in the middle of both ranges.