DETERMINATION OF CADMIUM IN FOODSTUFFS AND PLANT MATERIALS BY FLOW INJECTION-SPECTROPHOTOMETRY INCLUDING ION-EXCHANGE

A flow-injection system with a minicolumn packed with a strongly basic anion exchanger (AG1-X8 resin, 200-400 mesh) is proposed for the spec trophotometric determination of cadmium in foodstuffs, plants and simi lar based on the formation of a cadmium iodide-Malachite Green (MG) as sociate. Improved sensitivity and selectivity are attained since cadmi um is in-line concentrated as chlorocomplexes whereas lead, copper and other potential interferents are discarded. Reagent compositions, flo w rates, commutation times, mean available time for chlorocomplexes fo rmation, and conditions for concentration and elution were investigate d. A 2.0 M NaCl-0.1 M HCl solution was elected for chlorocomplexes for mation, and a 90-s concentration time was set. The eluant, also sample carrier stream, was a 2.0 M NaNO3 plus 0.1 M HNO3 solution. The propo sed system handles about 25 samples per hour (2.50-25.0 mu g Cd l(-1)) , consuming ca. 8 ml of sample, 0.25 mg MG and 0.41 g KI per determina tion. The detection limit is 0.11 mu g Cd l(-1). Results are precise ( R.S.D. 2.72 and 2.26% for 5.12 and 19.7 mu g Cd l(-1)) and in agreemen t with certified values of standard reference materials. Recoveries wi thin 99.1 and 111.2% were found. With two resin minicolumns, the appli cability of the system is expanded, and samples solubilized with nitri c and perchloric acids can also be run. The first minicolumn stands fo r in-line perchlorate removal before chlorocomplex formation, and the second one for cadmium concentration. Although more complex, similar s ystem performance and results quality relatively to the system with a single minicolumn are attained.