微波碱性体系消解-电感耦合等离子体发射光谱法测定固体废物中的六价铬

六价铬Cr(Ⅵ)是建设用地土壤及固体废物环境监测的必测指标之一,为了配套现行土壤环境质量标准,建立操作简便、准确精密的Cr(Ⅵ)前处理和分析测定方法势在必行。本文采用0.1mol/L磷酸氢二钠溶液(pH=9.0)作为提取剂,微波炉消解,在优化的微波消解温度和时间内,保证了对固体样品基体的破坏作用,将晶格中的Cr(Ⅵ)全部释放到溶液中,并有效抑制了Cr(Ⅲ)氧化。用0.45μm滤膜在pH=9.0条件进行过滤后,可以将六价铬(溶液)与三价铬(沉淀)分离,借助电感耦合等离子体发射光谱法(ICP-OES)完成样品溶液中Cr(Ⅵ)的定量。结果表明:当样品量为1.00g,微波消解温度为90℃,消解时间为20min时能够保证固体废物中Cr(Ⅵ)的完全提取及准确测定。方法检出限为0.057mg/kg,相对标准偏差(n=7)低于3.20%,与HJ 687标准方法进行比对,测得的相对偏差介于-5.6%~7.6%;实际固体废物中Cr(Ⅵ)的加标回收率为94.3%~96.6%。与前人相关的电感耦合等离子体发射光谱法(检出限0.83mg/kg,加标回收率均值87.2%)相比,本方法的检出限更低,样品前处理时间更短,自动化程度高,可应用于环境监测领域。

Determination of Hexavalent Chromium in Solid Waste by Inductively Coupled Plasma-Optical Emission Spectrometry with Microwave Digestion

BACKGROUND:Hexavalent chromium is one of the necessary indices for monitoring the soil environment of solid waste and construction land.OBJECTIVES:To establish a simple,accurate and precise method for the determination of Cr(Ⅵ).METHODS:Using 0.1mol/L disodium hydrogen phosphate solution(pH=9.0)as the extractant,the sample was treated by microwave digestion at the optimized temperature and time,ensuring the destruction of the solid sample matrix.All Cr(Ⅵ)in the lattice was dissolved into the solution,and oxidation of Cr(Ⅲ)was effectively inhibited.The hexavalent chromium(solution)and trivalent chromium(precipitation)was separated by 0.45μm filter membrane at pH=9.0.Cr(Ⅵ)in the sample solution,and the content of Cr(Ⅵ)was determined by inductively coupled plasma-optical emission spectrometry(ICP-OES).RESULTS:When the sample quantity was 1.00g,the microwave digestion temperature was 90℃,and the digestion time was 20min,the complete extraction and accurate determination of Cr(Ⅵ)in solid waste was guaranteed.The detection limit was 0.057mg/kg,the relative standard deviation(n=7)was lower than 3.20%,compared with HJ 687 standard method,the relative deviation is-5.6%-7.6%,and the recoveries of Cr(Ⅵ)in solid waste were 94.3%and 96.6%.Compared with the previous ICP-OES method with the detection limit of 0.83 mg/kg and recovery of 87.2%,the detection limit of this method was lower by 10 times.CONCLUSIONS:The proposed method has a lower detection limit,short sample pretreatment time,and high degree of automation and can be widely used in the field of environment monitoring.