Determination of Lead, Cadmium and Chromium in Grain by Graphite Furnace Atomic Absorption Spectrometry with Microwave Digestion Based on Deep Eutectic Solvent

A method for the determination of lead, cadmium and chromium in grain by graphite furnace atomic absorption spectrometry (GFAAS) with microwave digestion based on deep eutectic solvent (DES) was proposed. Urea was used as hydrogen bond acceptor and glycerol was used as hydrogen bond donor. Both of the above were added at a molar ratio of 1∶2, and then mixed at a rotating speed of 700 r·s^-1 and a temperature of 90 ℃ until the liquid was clear and transparent to form DES. 2 g of the prepared DES was added into 0.2 g of the grain sample to be tested, and the solution was treated for 5 min by microwave digestion in 30% (mass fraction) hydrogen peroxide solution and 5 mL of 5% (volume fraction) nitric acid solution under the condition of 500 W of power and 90 ℃ of temperature. The digestion solution was made its volume up to 10 mL, and then filtered, in which lead, cadmium and chromium were determined by GFAAS. As shown by the results, linear relationships between values of the corresponding absorbance and mass concentration of lead, cadmium and chromium were found in definite ranges, with detection limits (3s/k) not greater than 0.010 mg·kg^-1. Test for recovery was made by standard addition method, giving results in the range of 89.0%-101%, with RSDs (n=6) of the determined values less than 5.0%. Compared with the national standard method, the determination results obtained by this method were basically consistent, and could meet the detection limit requirements specified by the national standard method, which could be used for the sampling detection of heavy metal elements in daily grain samples.