流动注射-火焰原子吸收光谱法测定痕量铅——磷酸盐沉淀吸附在线富集

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

在流动注射-火焰原子吸收光谱法(FI-FAAS)测定铅(Ⅱ)的流路中设计了铅(Ⅱ)的磷酸盐沉淀在线富集的编结反应器,痕量铅(Ⅱ)与2.0×10-9mol.L-1磷酸二氢钾溶液在微酸性条件下在反应器中反应。当试样溶液的进样体积固定为8.00 mL,采用的富集流速为4.4 mL.min-1,富集时间为90 s,生成的铅(Ⅱ)的磷酸盐沉淀吸附于聚四氟乙烯反应管的内壁,毋需过滤,直接用2.0 mol.L-1硝酸流入管内使铅(Ⅱ)的沉淀溶解,溶液中铅(Ⅱ)按选定条件进行FAAS检测。按上述条件,可使增强系数(N)达到20,铅(Ⅱ)的检出限(3σ)达到23μg.L-1。对铅(Ⅱ)0.50 mg.L-1的标准溶液平行测定6次,算得测定结果的相对标准偏差为3.1%。用此方法分析了2件粉饼样品,测定值的相对标准偏差(n=6)分别为2.2%和4.1%。以此样品作基体进行回收试验,测得平均回收率为91%。

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 （3a） of 23μg · 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 oI 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%.