土壤中六价铬含量的测定方法比对

Comparison of determination methods of hexavalent chromium content in soil

铬(Ⅵ)是土壤环境质量标准中规定的必测指标之一,对比两种测定方法的稳定性和准确性,解决标准方法测定结果的不稳定性和低含量样品测定的准确性。本文采用Na_(2)CO_(3)-Na OH碱性混合液作为提取液,通过恒温水浴振荡浸提土壤样品,再经冷却、过滤、调节pH值后分别用火焰原子吸收分光光谱仪(AAS)和电感耦合等离子体发射光谱仪(ICP-OES)测定。结果表明,AAS法测定时吸光值小,灵敏度低,结果不稳定,而ICP-OES法灵敏度高,干扰小;当样品量为5.00g时,ICP-OES方法检出限(0.10mg·kg^(-1))、相对标准偏差(n=7,0.92%~1.22%)低于AAS(0.54mg·kg^(-1),2.43%~4.23%);标准物质验证实验结果相对误差也表现为ICP-OES法(0.38%)低于AAS法(3.87%),实际样品中铬(Ⅵ)的加标回收率分别为96.47%~103.40%(ICP-OES)和85.56%~117.43%(AAS)。ICP-OES法检出限低且具有良好的重复性、准确性与回收率,更适用于低浓度环境土壤监测领域。

Hexavalent chromium is one of the necessary indexes stipulated in soil environmental quality standard.The stability and accuracy of the two methods were compared to solve the instability of the standard method and the accuracy of low-content samples.A mixture of sodium carbonate and sodium hydroxide was used as the extraction solution,constant temperature water bath oscillation extraction of soil samples,after cooling,filtration and pH adjustment,they were determined by flame atomic absorption spectrometer(AAS)and inductively coupled plasma emission spectrometer(ICP-OES).The results show that the absorption value of AAS method is small,the sensitivity is low,and the results are unstable,while the sensitivity of ICP-OES method is high,and the interference is small;When the sample size was 5.00g,the detection limit(0.10 mg·kg^(-1))and relative standard deviation(n=7,0.92%~1.22%)of ICP-OES were lower than those of AAS(0.54mg·kg^(-1),2.43%~4.23%);the relative error RE of the experimental results of reference material verification was also lower than that of AAS(3.87)by ICP-OES(0.38%),and the recoveries of hexavalent chromium in actual samples were 96.47%~103.40%(ICP-OES)and 85.56%~117.43%(AAS),respectively.The ICP-OES method has low detection limit,good repeatability,accuracy and recovery,and is more suitable for low-concentration environmental soil monitoring.