基体稀释或基体匹配石墨炉原子吸收光谱法测定土壤样品中铅和镉

用石墨炉原子吸收光谱法测定土壤样品中Pb和Cd时,有时候直接按照方法标准GB/T 17141—1997操作,测定结果不能满足质控要求。研究结果表明,目标元素系列标准溶液中,分别含和不含土壤基体元素Na、Mg、Al、Si、Fe、Ca等元素混合成分时,校准曲线斜率明显不同。为减小基体效应的影响,基于文献调研和实验结果,对上述方法标准实验步骤进行了下列改进:(1)取相同体积实际样品消解液混合后,定量加入到用于建立校准曲线的系列标准溶液中,用于基体匹配;(2)对消解液进行适度稀释,仍采用标准溶液建立校准曲线。用4个土壤标样和土壤样品加标测定结果对改进后的方法进行了验证,结果表明,基体稀释法测定Pb的回收率范围分别为90.4%~114%;测定低含量Cd时,回收率范围为84.1%~125%。基体匹配法测定Pb和Cd的回收率范围分别为93.0%~105%和102%~119%,基本满足土壤样品中重金属回收率为80%~120%的质控要求。样品中痕量镉在测定下限附近时,应严格控制稀释倍数,或采用基体匹配法测定。改进后的操作步骤适合日常检测工作中大批量土壤样品中Pb和Cd的准确测定。

Determination of lead and cadmium in soil samples by graphite furnace atomic absorption spectrometry based on matrix dilution or matrix matching

During the determination of lead and cadmium in soil sample by graphite furnace atomic absorption spectrometry, the results cannot meet the requirements of quality control sometimes if it is operated directly according to the standard GB/T 17141-1997. The results showed that the slope of calibration curve was significantly different when the standard solution series of target elements contained or did not contain the mixed elements of soil matrix elements including Na, Mg, Al, Si, Fe and Ca. In order to reduce the influence of matrix effect, the procedures in standard method above were improved based on literatures and experiments as follows: (1) the digestion solution of actual sample with same volume was mixed and then quantitatively added into the standard solution series for preparation of calibration curves for matrix matching; (2) the digestion solution was diluted appropriately and the calibration curves were still established with the standard solutions. The improved method was verified using four soil standard samples and spiked results of soil sample. The results showed that the recovery range of Pb in matrix dilution method was 90.4%-114%. For the low content of Cd, the recovery range was 84.1%-125%. The recovery range of Pb and Cd in matrix matching method was 93.0%-105% and 102%-119%, respectively, which could basically meet the quality control requirements of recovery for heavy metals in soil sample, i.e., 80%-120%. When the content of trace cadmium in sample was near the lower determination limit, the dilution factor should be strictly controlled or the sample should be determined by matrix matching method. The modified operation procedures in this study were suitable for the accurate determination of Pb and Cd in large batches of soil samples in routing inspection.