微波消解-分光光度法测定水果中铅(Ⅱ)含量
Spectrophotometric Determination of Pb(Ⅱ) in Fruits with Microwave Assisted Sample Digestion
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摘要: 在pH 5.6的六次甲基四胺(简称六胺)缓冲介质中,铅(Ⅱ)与二甲酚橙(XO)及溴化十六烷基三甲铵(CTMAB)形成三元配合物,其吸收峰在570~580 nm之间。试验选择的显色反应条件:于25 mL总体积中依次加入400 g·L-1六胺溶液3.6 mL,2.0 g·L-1 XO溶液2 mL和2.0 g·L-1 CTMAB溶液2.5 mL,加水定容放置10 min,于波长570 nm处测量吸光度。制作了铅(Ⅱ)的质量浓度在0.2~1.0 mg·L-1范围内的标准曲线,线性关系良好。将上述方法用于测定水果中含铅量,水果样品(3.0 g)用硝酸(5 mL)和过氧化氢(2 mL)进行微波消解,所得溶液蒸缩至约1~2 mL,用水定容至50 mL。分取5.00 mL试液,按上述方法测定其中铅量。取5种水果样品进行分析,并同时用火焰原子吸收光谱法测定,所得结果表明两种方法的测定值之间无显著差异。Abstract: In a hexamine buffer medium of pH 5.6, a ternary coordination complex was formed among Pb(Ⅱ), xylenol orange (XO) and CTMAB, with its absorption maximum at 570-580 nm. Conditions for the color reaction were optimized and given as follows: in a total volume of 25 mL, 3.6 mL of 400 g·L-1 hexamine solution, 2.0 mL of 2.0 g·L-1 XO solution and 2.5 mL of 2.0 g·L-1 CTMAB solution were added; water was added to make up the volume to 25 mL and the solution was let to stay for 10 min. The absorbance of the solution was measured at 570 nm. Standard curve for Pb(Ⅱ) in the range of 0.2-1.0 mg·L-1 was prepared which was good in linearity. This method was applied to determination of Pb(Ⅱ) in fruit samples. The fruit sample (3.0 g) was treat by microwave assisted digestion with HNO3 (5 mL) and H2O2 (2 mL). The solution obtained was evaporated to a volume of 1-2 mL, and then made up the volume to 50 mL with water. An aliquot of 5.00 mL was taken for the determination. Five samples of different fruits were analyzed by this method, and results were checked by analysis of the samples by FAAS. It was shown that no significant difference was found between the results of the 2 methods.