Spectrophotometric Determination of Pb(Ⅱ) in Fruits with Microwave Assisted Sample Digestion

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.