Determination of lead in shrimp with meso-tetra (3, 5-dibromo-4-hydroxyphenyl) porphyrine by spectrophotometry

A spectrophotometric method for the determination of trace lead in foods with meso-tetra (3, 5-dibromo-4-hydroxyphenyl) porphyrine as chromogenic reagent had been studied. The effect of meso-tetra (3, 5-dibromo-4-hydroxyphenyl) porphyrine amount, pH, top, emperature and time on the stability of the formed complex were assayed. An excellent method used to determine the lead in shrimp had been ascertained. The optimal parameter under the experimental conditions was as followed:0.40mL 0.3mol/L NaOH, 100℃ water-bathing for 3min. The soret band of the complex was at 479nm. Beer’s law was obeyed in the range of 0.1～1.0μg/mL of Pb. The regressive equation of standard curve was y=0.9237+0.0115 (R=0.9995) and apparent molar absorptivity was 1.528×10⁸ L/ (mol·cm) . In order to achieve the lead ions enrichment, the samples were treated by traditional cineration and the lead was enriched with method of precipitation. Experimental results indicated that the method was easy to operate and had a good reproducibility. It could be used to determine trace amounts of lead in shrimp. Results were satisfactory.