The determination of lead in preserved food by spectrophotometry with dibromohydroxyphenylporphyrin

A highly sensitive and selective method for the spectrophotometric determination of lead in preserved food has been developed, which is based on the colour reaction of lead(II) with dibromohydroxyphenylporphyrin. In 0.1 mol l−1 sodium hydroxide, the reagent reacts with lead(II) and TritonX-100 to form a 1:2:2 ternary complex with a maximum absorption at 479 nm. The reaction can be completed rapidly at room temperature and the absorbance is stable for at least 12 h. The molar absorption coefficient of the complex, Sandell’s sensitivity, the detection limit and the relative standard deviations were found to be 2.2 × 105 l mol−1 cm−1, 0.000942 μg cm−2, 1.2 ng ml−1 and 1.1%, respectively; from 0–0.5 g ml−1 lead(II) the absorbance obeyed Beer’s law. The influence of reaction variables and the effect of foreign ions were studied in detail. The experiments indicated that common salt can be tolerated in considerable amounts, which is an advantage over other methods including atomic absorption spectrometry, which it is important for preserved food. The proposed method has been applied to determine lead in various preserved foods and the result were not significantly different from those obtained by atomic absorption spectrometry with an extraction separation.