Spectrophotometric determination of lead in foods with dibromo-p-methyl-bromosulfonazo

The synthesis and purification of a new chromogenic reagent dibromo-p-methy l-bromosulfonazo (DBMBSA) are described. A method is proposed for the spect rophotometric determination of lead with DBMBSA. In 0.24 M phosphoric acid medium, which greatly increases the selectivity, lead reacts with DBMBSA to form a 1:2 blue complex, having a sensitive absorption peak at 638 nm. Und er the optimal conditions. Beer's law is obeyed over the range from 0 to 1 mug ml(-1) Pb(II) and the apparent molar absorptivity is 8.44 x 10(4) l mol (-1) cm(-1). The detection limit and the variation coefficient were found t o be 2.45 ng ml(-1) and 1.3%, respectively. It is found that, except for Ca (II) and Ba(II), all foreign ions studied do not interfere with determinati on. The interference caused by Ca(II) and Ba(II) can be easily eliminated b y prior extraction with potassium iodide-methylisobutylketone (KI-MIBK). Th e method has been applied to the determination of lead in foods with satisf actory results. (C) 2001 Elsevier Science B.V. All rights reserved.