Spectrophotometric Determination of Lead in Water Samples with Dibromo-tetraphenylporphyrin as Chromogenic Reagent

Dibromo-tetraphenyl-porphyrin (DBTPP) was used as a new chromogenic reagent for determination of lead(Ⅱ), and conditions for the colour reaction were studied. In a Na2HPO4-NaOH buffer solution of pH 12, and in the presence of Tween-80, a stable coordination complex with the molar ratio ［Pb(Ⅱ)∶(DBTPP)］ of 1 to 1 was formed, with its absorption max. at the wavelength of 472 nm. Value of apparent molar absorptivity was found to be 2.2×104L·mol-1·cm-1. Beer′s law was held in the range within 180 μg·L-1. The proposed method was applied to the determination of lead in environmental water samples, giving values of recovery in the range of 99.9%-102.0%.