微波辅助消解-固相萃取-氢化物产生-原子荧光光谱联用检测乌龙茶茶叶中无机砷

Determination of inorganic arsenic in Oolong tea leaves by microwave assisted digestion-solid phase extraction-hydride generation-atomic fluorescence spectroscopy

目的建立微波辅助消解-固相萃取-氢化物产生-原子荧光光谱法测定乌龙茶茶叶中无机砷的分析检测方法。方法以0.06 mol/L HNO_3-3%H_2O_2为消解液,在最大微波功率800 W下,120℃微波消解35 min,提取茶叶中的无机砷,并基于As(Ⅲ)、As(Ⅴ)、一甲基砷(monomethylarsonic acid,MMA)和二甲基砷(dimethylarsinic acid,DMA)解离常数的差异,通过强阴离子交换柱(strong anion exchange cartridge,SAX)实现无机砷和有机砷的有效分离,最后采用氢化物产生-原子荧光光谱法进行无机砷含量测定。结果在0~30μg/L浓度范围内,无机砷的标准曲线方程线性良好(相关性系数r=0.9994),检出限(limit of detection,LOD)为0.208μg/L,样品加标回收率在95.7%~103.6%,相对标准偏差为1.8%~6.8%。结论该方法采用微波辅助消解结合固相萃取提取、分离茶叶中无机砷,具有效率高、成本低、易操作等优点,且可实现乌龙茶茶叶中无机砷高选择性、高灵敏度的分离分析检测。

Objective To establish a method for determination of inorganic arsenic in Oolong tea leaves by microwave assisted digestion combined with solid phase extraction and hydride generation atomic fluorescence spectroscopy. Methods Inorganic arsenic was extracted from tea by microwave assisted digestion （MAD） in 0.06 mol/L HNO3-3%H202, and the digestion was performed at 120℃ for 35 min under the maximal power of 800 W. Inorganic arsenic and organic arsenic were seperated from other arsenic species using strong anion exchange cartridge （SAX） based on the difference of dissociation constants among As（III）, As（V）, monomethylarsonic acid （MMA） and dimethylarsinic acid （DMA）, and the concentration of inorganic arsenic was finally detected by hydride generation atomic fluorescence spectrometry. Results Inorganic arsenic had a good relationship with correlation coefficients of 0.9994 in the range of 0-30 μg/L. The limit of detection （LOD） was 0.208 μg/L, the recoveries of sample addition were 95.7%-103.6% with the relative standard deviations （RSDs） were 1.8%-6.8%. Conclusion The method adopts solid phase extraction to separate inorganic arsenic from tealeaves, and it has the advantages of high efficiency, low cost and easy operation, and can prove highly sensitiveand specific for inorganic arsenic quantification in Oolong tea leaves.