提出了石墨炉原子吸收光谱法测定食盐中镉含量的方法。称取食盐样品0.5 g,用1%(体积分数,下同)硝酸溶液溶解并定容至50 mL,摇匀,配制成待测样品溶液。以1%硝酸溶液为溶剂,配制成含10 g·L^-1磷酸二氢铵和10 g·L^-1抗坏血酸的基体改进剂。测定时,采用自动进样器吸取1.0 μL基体改进剂至20 μL待测样品溶液中。优化后的石墨炉升温条件:干燥温度为120℃,灰化温度为350℃,原子化温度为700℃,净化温度为2 700℃。结果显示:镉的质量浓度在0.1~2.0 μg·L^-1内与其对应的吸光度呈线性关系,检出限(3s/k)为0.001 mg·kg^-1;对含不同质量分数镉的氯化钠加标溶液进行测定,测定值的相对标准偏差(n=6)均小于4.0%;对不同类型的食盐样品进行加标回收试验,镉回收率为92.0%~101%。

A method for the determination of Cd in edible salt by graphite furnace atomic absorption spectrometry was proposed. Edible salt sample (0.5 g) was dissolved and made its volume up to 50 mL with 1% (φ) nitric acid solution to prepare the test sample solution after shaking. 1% (φ) nitric acid solution was used as solvent, the matrix modifier containing 10 g·L^-1 ammonium dihydragen phosphate and 10 g·L^-1 ascorbic acid was obtained. Matrix modifier (1.0 μL) was absorbed into the test sample solution (20 μL) by an automatic sampler. The optimized heating conditions of graphite furnace were as follows: the drying temperature of 120 ℃, the ashing temperature of 350 ℃, the atomization temperature of 700 ℃, and the purification temperature of 2 700 ℃. As shown by the results, linear relationship between values of mass concentration of Cd and its absorbance was kept in the range of 0.1-2.0 μg·L^-1, with detection limits (3s/k) of 0.001 mg·kg^-1. Spiked solutions of sodium chloride containing different mass fractions of Cd were determined, and RSDs (n=6) of the determined values were less than 4.0%. Test for recovery was made on different types of edible salt samples by standard addition method, giving results in the range of 92.0%-101%.