应用1-(2-吡啶偶氮)-2-萘酚(简写作PAN)-镍(Ⅱ)共沉淀体系,以锰(Ⅱ)为内标,在pH 9的氨性缓冲溶液中对食盐中痕量铅(Ⅱ)进行快速共沉淀富集,并用火焰原子吸收光谱法测定铅的含量,对共沉淀条件作了优选.在优化的条件下,试液中作为内标的锰(Ⅱ)及铅(Ⅲ)离子均定量地与PAN-Ni(Ⅱ)共沉淀析出.锰(Ⅱ)、铅(Ⅱ)及镍(Ⅱ)均匀地存在于沉淀中,而且在铅(Ⅱ)、锰(Ⅱ)之间或镍(Ⅱ)、锰(Ⅱ)之间存在着一定的比例关系.因此,根据共沉淀中铅(Pb1)及锰(Mn1)的吸光度APb1,AMn1的比值即可求得铅的含量(w%),原试样中铅含量(Pb0)可由下式计算：mPb0=APb1/AMn1·mMn0.试验结果表明,经过共沉淀分离,基体干扰已予消除.此方法的检出限为3.18×10-2mg·L-1.应用于3种不同来源的食盐的分析,算得铅含量测定值的RSD(n=6)均小于4.3%,回收率测得值在95.4%至101.6%之间.

Trace amounts of lead in table salt were separated by co-precipitation with PAN-Ni(Ⅱ),and adding Mn(Ⅱ) ion as internal standard.Conditions for co-precipitation were optimized.Under the optimized reaction conditions,the internal standard Mn(Ⅱ) and Pb(Ⅱ) ions in the sample were quantitatively co-precipitated by PAN-Ni(Ⅱ),and both of the Mn(Ⅱ) and Pb(Ⅱ),also including Ni(Ⅱ) were present in the precipitate with good homogeneity,and a definite ratio was kept between Pb(Ⅱ) and Mn(Ⅱ),or between Ni(Ⅱ) and Mn(Ⅱ).The mass of lead in the sample was calculated from the ratio of absorbances APb1 and AMn1 of lead (Pb1) and manganese (Mn1) found in the co-precipitate.Lead content (Pb0) in the original sample was calculated by the following formula: mPb0=APb1/AMn1·mMn0.It was shown by experimental results that by the separation mentioned above,the matrix interference was effectively eliminated.Detection limit of this method was found to be 3.18×10-2mg·L-1.In the analysis of 3 kinds of table salt by this method.RSD′s (n=6) obtained were less than 4.3%,and recoveries in the range of 95.4%-101.6% were found.