FI-FAAS Determination of Trace Amounts of Lead with On-line Enrichment by Phosphate Precipitation

A knotted reactor for on-line enrichment of Pb(Ⅱ) by phosphate precipitation was designed and connected in manifold for FI-FAAS determination of lead.Trace amount of lead(Ⅱ) was reacted with 2.0×10-9mol·L-1 KH2PO4 solution in a slightly acidic medium in the knotted reactor.When the volume of sample solution introduced was fixed at 8.00 mL,the flow-rate of the solution for enrichment was taken at 4.4 mL·min-1,and time for enrichment was taken for 90 s,Pb(Ⅱ) was precipitated as phosphate and adsorbed on the inner wall of the PTFE reaction tubing of the knotted reactor.Solution of 2.0 mol·L-1 HNO3 was passed through the reaction tubing to dissolve the phosphate precipitate,and the solution obtained was used for FAAS determination of lead according to the instrumental working conditions prescribed.Under the optimum conditions described above,values of enhancement factor(N) of 20,and of detection limit(3σ) of 23 μg·L-1 were achieved.Value of RSD(n=6) calculated from the data of 6 determination of Pb(Ⅱ) at the concentration of 0.50 mg·L-1 by the proposed method was 3.1%.In the application of the method to determine trace amounts of lead in 2 cosmetic samples,values of RSD′s(n=6) found were 2.2% and 4.1% respectively.Value of average recovery found by adding standard lead solution to these substantial samples was 91%.