The technique of gas-phase atomisation of the volatile hydrides in a heated silica tube and measurement of the resulting atomic-absorption signal has been extended to the determination of lead in air, water and vegetation. The sample solutions, containing 0.70/, V / V of nitric acid or 1.0% V / V of perchloric acid, are made to react with 12% V / V hydrogen peroxide solution followed by 4% m/ V sodium borohydride solution by means of a peristaltic proportioning pump. The gaseous hydrides generated are swept by a stream of nitrogen into a heated silica tube and the absorbance of lead a t 217 nm is recorded. The effects of interferences and their elimination are discussed. Results obtained on a few typical samples by the proposed method and a n alternative method are presented.A sensitivity of 0.6 ng ml-l and a detection limit of 0.1 ng ml-l have been achieved. The relative standard deviation of the method is 2.5% a t a lead concentration of 10 ng ml-I. Up to 50 samples can be analysed in 1 d.Several papers have been published recently on the determination of most of the Group 4A, 5A and 6A elements by their conversion into gaseous hydrides followed by gas-phase atomisation in a heated silica tube and measurement of the atomic-absorption signals.1-6 Aqueous solutions of sodium borohydride have increasingly been used for hydride generation. These methods allow the separation of the analytes from the interfering matrices and provide sensitivities that are several orders of magnitude greater than those obtained with the conventional flame methods. Gas-phase atomisation techniques can be easily automated, and they are generally recognised to be less susceptible to interferences and give better precision and accuracy than the carbon rod or graphite furn
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