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 spectrophotometric determination of cadmium in foodstuffs, plants and similar based on the formation of a cadmium iodide-Malachite Green (MG) associate. Improved sensitivity and selectivity are attained since cadmium is in-line concentrated as chlorocomplexes whereas lead, copper and other potential interferents are discarded. Reagent compositions, flow rates, commutation times, mean available time for chlorocomplexes formation, and conditions for concentration and elution were investigated. A 2.0 M NaCl-0.1 M HC1 solution was elected for chlorocomplexes formation, 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 proposed system handles about 25 samples per hour (2.50–25.0 μg Cd l−1), consuming ca. 8 ml of sample, 0.25 mg MG and 0.41 g KI per determination. The detection limit is 0.11 μg Cd l−1. Results are precise (R.S.D. 2.72 and 2.26% for 5.12 and 19.7 μg Cd l−1) and in agreement with certified values of standard reference materials. Recoveries within 99.1 and 111.2% were found. With two resin minicolumns, the applicability of the system is expanded, and samples solubilized with nitric and perchloric acids can also be run. The first minicolumn stands for in-line perchlorate removal before chlorocomplex formation, and the second one for cadmium concentration. Although more complex, similar system performance and results quality relatively to the system with a single minicolumn are attained.