Spectrophotometric Determination of Trace Lead in food with Trihydroxyphenylfluorone in Microemulsion after Sulphydryl Dextrane Gel for Preconcentration and Separation

A highly sensitive and selective spectrophotometric method is proposed for the determination of trace lead in food. The method is based on the reaction of lead(II) with a new analytical reagent trihydroxyphenylfluorone (TH-PF). TH-PF reacts with lead(II) and form a stable 1 : 2 complex at pH 10.40. Its apparent molar absorption coefficient and Sandell´s sensitivity at 580 nm are 4.56 times 10⁴ L/mol/cm and 4.54 times 10^-3 mug/cm2. Beer´s law is obeyed in the range of 0-1.6 mug/mL of lead(II). In addition, the optimal condition for the determination with different microemulsion medium was investigated in detail. Sulphydryl dextrane gel (SDG), in which sulphydryl group has a big share, is a good type metallic ion adsorbent. It presents the advantages of higher adsorption capacity, better reuse ability and higher mechanical stability. Therefore, the coexistent metal ions can be separated effectively and lead can be enriched by SDG, greatly improving the selectivity and sensibility of the system. The method is used to determine trace lead in food with satisfactory results.