提出一种基于低共熔溶剂(DES)的微波消解-石墨炉原子吸收光谱法(GFAAS)测定粮谷中铅、镉、铬含量的方法。采用尿素作为氢键受体、丙三醇作为氢键供体,二者按物质的量比为1∶2加入,在转速为700 r·s^-1、温度为90 ℃下搅拌混合至澄清透明的液体,形成DES。将2 g制备好的DES加至0.2 g待测粮谷样品中,并用30%(质量分数)过氧化氢溶液2 mL和5%(体积分数)硝酸溶液5 mL在功率500 W、温度90 ℃的条件下微波消解5 min,所得消解液用水定容至10 mL,经过滤后,采用GFAAS测定其中铅、镉和铬的含量。结果表明:铅、镉、铬的质量浓度在一定范围内与对应的吸光度呈线性关系,检出限(3s/k)均不大于0.010 mg·kg^-1。按照标准加入法进行回收试验,回收率为89.0%~101%,测定值的相对标准偏差(n=6)均小于5.0%。该方法与国家标准方法比较,所得测定结果基本一致,且能够满足国家标准方法规定的检出限要求,可用于日常粮谷样品中重金属元素的抽样检测。

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.