低温灰化-悬浮液进样石墨炉原子吸收光谱法测定煤中镉

针对煤质复杂,而煤中的镉元素具有低含量且易挥发的特点,提出了采用氧等离子体低温灰化技术对煤进行预处理,再加入硝酸钯作为基体改进剂使镉在灰化过程中生成难离解物质,建立了悬浮液进样石墨炉原子吸收光谱法(GFAAS)测定煤中镉的方法。研究过程中主要探讨了样品基质的影响,通过对比分析低温灰化前后的样品,发现低温灰化处理明显提高了分析的灵敏度和精密度;优化了悬浮液样品的灰化温度和原子化温度及基体改进剂的用量,确定灰化温度和原子化温度分别为650 ℃和2 200 ℃,基体改进剂硝酸钯的最佳质量浓度为1.0 g/L。实验表明,在优化条件下,标准悬浮液样品中镉在0.1～2.0 μg/L范围内呈现较好的线性关系,线性相关系数为0.999 5。方法检出限为0.012 mg/kg。对煤实际样品和标准物质进行分析,相对标准偏差(RSD,n=5)为2.9%～5.9%,测定结果与密闭消解法处理样品后的测定值或认定值吻合。

Determination of cadmium in coal by low temperature ashing-slurry sampling graphite furnace atomic absorption spectrometry

The composition of coal is complicated. The content of cadmium in coal is low, and it is easily volatile. According to these characteristics, the coal was firstly pretreated by oxygen plasma low temperature ashing. Then, the palladium nitrate was added as matrix modifier to make cadmium form non-dissociative substance in ashing process. The determination method of cadmium in coal by graphite furnace atomic absorption spectrometry(GFAAS) with slurry sampling was established. The influence of sample matrix was mainly studied. The samples before and after low temperature ashing were compared and analyzed. The results indicated that the analytical sensitivity and precision could be significantly improved by low temperature ashing treatment. The ashing temperature and atomization temperature of slurry sample and the dosage of matrix modifier were optimized. The ashing temperature and atomization temperature was 650 ℃ and 2 200 ℃, respectively. The optimal mass concentration of matrix modifier (i.e., palladium nitrate) was 1.0 g/L. Under the optimized conditions, the standard slurry sample showed good linear in range of 0.1-2.0 μg/L for cadmium. The linear correlation coefficient was 0.999 5. The detection limit was 0.012 mg/kg. The actual sample and certified reference material of coal were analyzed according to the experimental method. The relative standard deviation (RSD, n=5) was between 2.9% and 5.9%. The found results were consistent with those obtained by airtight digestion method or the certified values.