DETERMINATION OF CADMIUM IN FERTILIZERS BY FLOW-INJECTION SPECTROPHOTOMETRY

A flow-injection procedure for spectrophotometric determination of cad mium in fertilizers based on formation of the blue ternary complex bet ween cadmium, iodide and Malachite Green (MG) is proposed. Addition or der and concentrations of reagents, interaction time between iodide an d MG, flow rates, pH and temperature for ternary complex formation, su rfactant addition, and presence of potential interferent ions were stu died. A 30-s interaction between iodide and MG, a temperature of 20 de grees C and use of picolinic acid for copper masking were selected. Li nearity of the calibration graph was improved with cadmium addition. F or selectivity enhancement, masking agents, kinetic discrimination, an d ion-exchange separation were investigated and a Chelex-100 resin min icolumn (50-100 mesh) was employed for in-line interferent removal. Th e proposed system is very stable and handles about 60 samples per hour (10.0-100.0 mu g Cd l(-1)) corresponding to 0.105 mg MG and 166 mg KI consumed per determination Linearity of the calibration plot is obser ved up to 200 mu g Cd l(-1), the detection limit being 2 mu g Cd l(-1) . Results are precise (R.S.D. = 1.3% and 4.0% for 93.0 and 35.3 mu g C d l(-1)) and in agreement with tungsten coil atomic absorption spectro metry. Accurate results are also obtained for lobster and soya bean sa mples.