Abstract
A method was proposed for the rapid and sensitive determination of lead by atomic absorption spectrometry after hydride evolution process. Compared with the cases using borohydride solution alone as a reductant, the sensitivity was enhanced extremely by the addition of dichromate, hydrogen peroxide or persulfate to the acidic solution of lead(II) prior to the injection of borohydride solution. Permanganate also exhibits such enhancement effect in some grade. When dichromate is used together with borohydride, malic acid or tartaric acid should be used as the acid. Various factors affecting the evolution of lead hydride, especially acids (and its acidity) and the concentration of above sensitivity enhancement reagents, were investigated. The determination procedure is as follows: Five to ten cm3 of sample solution was put into a reaction vessel (Hitachi Co., Ltd.), reagents were added, and the solution having one of the following compositions was prepared; (A) 0.25 M malic acid (tartaric acid)-0.025 M dichromate, (B) 0.5 M HNO3 (HCl, HClO4, 0.25 M H2SO4)-1.3 M H2O2, (C) 0.3 M HNO3 (HCl, HClO4)-0.12 M K2S2O8. The volume of the solution was adjusted to 20 cm3. After the injection of 5 cm3 of w/v NaBH4, the evolved lead hydride was introduced into nitrogen-hydrogen flame of the atomic absorption spectrometer. The detection limit of the method (S/N=2) is 15, 20, and 20 ng for (A), (B), and (C) system, respectively. The calibration graph was linear up to 1.5μg Pb. Effect of diverse ions on the determination of lead was also examined.
