Spectrophotometric determination with a chromogenic reagent of lead in vegetables

A method was developed for the simple, selective, and sensitive spectrophotometric determination of lead in vegetables with synthesized chromogenic reagent 3-[(2,6-dibromo-4-methylphenyl)diazenyl]-4,5-dihydroxy-6-[(2,4,6-tribromophenyl)diazenyl]naphthalene-2,7-disulfonic acid (DBMTBA; 1). In 0.25 M phosphoric acid medium, which greatly increases the selectivity, lead reacts with DBMTBA to form a 1:2 blue complex, which shows maximum absorption at 646 nm. Under optimal conditions, Beer's law is obeyed over the range from 0.09 to 0.8 microg ml(-1) Pb2+, and the apparent molar absorptivity is 1.024x10(5) l mol(-1) cm(-1). The detection limit and the variation coefficient were found to be 2.09 microg ml(-1) and 1.0%, resp. The proposed method has been applied successfully for the determination of lead in vegetables (Solanum melongena fruits, tomato fruits, Ablemoschus esculentus leaves, and Daucous carota leaves) with satisfactory results.