Determination of Cadmium in Rice by Microwave Digestion and Graphite Furnace Atomic Absorption Spectrometry

An analytical method for cadmium (Cd) in rice by microwave digestion and graphite furnace atomic absorption spectrometry (AAS) was developed. A sample of 0.50g was predigested overnight in 7mL of nitric acid. The mixture was treated with 2mL of hydrogen peroxide solution and immediately exposed to microwave irradiation. The digested solution was evaporated to just before dryness on a hotplate and then made up to 10mL with 0.2% nitric acid. Cd in the sample solution was determined by graphite furnace AAS using a calibration method. 0.5% ammonium dihydrogen phosphate/0.2% nitric acid and 2% ascorbic acid were used as matrix modifiers. Recoveries of Cd added to rice were 97-108%, the CV was 1.6-6.3% and the detection limit was 5ng/g. Cd was detected at 28-96ng/g in polished rice, 18-226ng/g in brown rice and 7-49ng/g in cooked rices.