The determination of trace lead in Chinese medicinal herbs by flow injection analysis in polyethyleneglycol medium

In this work, a new flow injection analysis (FIA) for the determination of Pb2+ in Chinese medicinal herbs was developed. In the buffer solution of borax-NaOH (pH 10.5), Pb2+ reacted with 2-[(5-bromo-2-pyridyl)-azo]-5-(diethyl-amino)phenol (5-Br-PADAP) to form a complex. The experimental results showed that the sensitivity was enhanced in the presence of polyethyleneglycol-800 (PG-800). The main factors affecting the determination were investigated in detail. Under the optimum conditions, the linear range and detection limit is 0.0-0.3 μg/mL and 1.5 ng/mL (correlation coefficient r = 0.9996), respectively. The linear regression equation is A = −0.005 + 0.60c (μg/mL). The sample throughout is 10 h−1. Foreign substrates effects were also investigated. The proposed method has been successfully applied to the determination of lead in reference material, goldthread and lepidium seed.