Semi-automated determination of lead by hydride generation and atomic-absorption spectrophotometry

Abstract

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<ace atomisation meth~ds.~-l* The latter methods are susceptible to handling and manipulation errors. Pollock and West7 investigated the determination of lead and a few other elernents by a hydride generation method but failed to obtain absorbance signals for lead even at a. concentration of 100 pg ml-l in aqueous solution.Thompson and Thomerson,2 using a similar appiroach, investigated the determination of lead together with antimony, arsenic, bismuth, germanium, selenium, tellurium and tin in aqueous solutions. They claimed to be the first to achieve the generation of plumbane for analytical purposes by using an aqueous solution of sodium borohydride but concluded that the efficiency of conversion of lead into its hydride was poor compared with other elements.This paper, to the best of our knowledge, offers for the first time a sensitive, precise, accurate and automated procedure for the determination of lead using a combination of hydride generation and atomic-absorption spectrophotometiy. Experiment a1 Reagentsdemineralised. sodium hydroxide solution and filter.All of the reagents used were of analytical-reagent grade.

Electrochemical Generation of Lead Volatile Species as a Method of Sample Introduction for Lead Determination by Atomic Absorption Spectrometry

“…Plumbane (PbH 4 ) production and subsequent lead quantitative determination was first described by Thompson and Thomerson [23]. Further applications of this type of methodology have been published [24][25][26][27][28][29][30][31][32][33]. In most of them oxidation of Pb 2 + to Pb 4 + , as a previous step for plumbane generation, is highlighted as the main difficulty of the method.…”

Reagent injection FIA system for lead determination by hydride generation - quartz-tube atomic absorption spectrometry

“…Consequently, its generation process is considered more complex and is assumed to take place in two stages: oxidation of lead (II) to lead (IV) and generation of the hydride from the higher oxidation state, which makes it necessary to use a third reagent (in most cases a strong oxidizing agent), in addition to the acid medium and tetrahydroborate. The reagents most frequently added to the reaction medium are: i) strong oxidants, such as H 2 O 2 , (NH 4 ) 2 S 2 O 8 , K 2 Cr 2 O 7 , and KMnO 4 with inorganic acids (HNO 3 [3,4,5,6], HCl [7,8]), organic acids (tartaric, malic, or lactic acid) [9,10], or combinations of both types of acid [11]. Other reagents used include chelating agents (Nitrous-R salt [13], PAN'S [14], and different surfactants in acid medium [15]).…”

“…The generation of hydrides as a method of sample introduction in quartz-tube AAS systems, in particular lead hydride, has been carried out in batch [2,7,9,10,14,15], in continuous flow [3,8], and by flow injection systems (FIA) [4,5,6,11,12,13]. Application of the flow injection technique to hydride generation, combined with atomic spectroscopy, has given rise to numerous analytical methods characterized by low sample and reagent consumption and, in most cases, fewer interferences [16].…”

Flow-injection determination of lead by hydride generation and conductometric detection

“…A recent review by Madrid and Ca´mara gives an overview of the topic [10]. It is also possible to use continuous-flow or flow-injection methods in order to reduce the number of manipulations required [11][12][13][14][15][16]. In flow-injection analysis the P.C.…”