Determination of Pb(II) in natural water with dibromo-p-methyl-sulfonazo by the light-absorption ratio variation approach

Pb ions can react sensitively with dibromo-p-methylsulfonazo (DMSA) to form a blue complex, whose absorption is maximal at 630 nm. By means of the light-absorption ratio variation approach (LARVA), the direct determination of Pb was developed in 0.3 M nitric acid and plots of Delta A_r^{-1} vs. c_{Pb}^{-1} are linear where Delta A_r is the light-absorption ratio variation and c_{Pb} Pb(II) concentration is between 0 and 5.0 mg/L. The limit of detection (3sigma) of Pb(II) is only 0.02 mg/L. This method was applied to direct analysis of natural water with satisfactory results.