Application of Sequential Injection Analysis to the Assay of Lead Retention Characteristics by Poly(vinylpyrrolidone): Trace Analysis of Lead in Waters

Abstract

Because heavy metals are usually present in water at trace levels, their determination can only be performed by highly sensitive analytical methodologies, namely electrothermal atomic absorption spectrophotometry (ETAAS) 1 , which is the most widely used. This technique is very expensive, though, as far as its purchase and daily use are concerned. Flame atomic absorption spectrophotometry (FAAS) is much cheaper and less complex in terms of handling, but its sensitivity is too low for this type of determination. Therefore, a preconcentration procedure is required both for minimizing the matrix interferences and improving the detection limit. The preconcentration of heavy metals in natural water has been performed by means of evaporation, solvent extraction 2,3 , ion-exchange and chelating resins 4-7 as well as coprecipitation. 8 When automating these procedures in continuous-flow units, faster determinations and a better quality of results are attained.Automatization by preconcentration in a homogeneous medium, called liquid-phase polymer-based retention (LPR) [9][10][11][12] , is also proposed. It consists of using soluble polymers, such as poly (vinylpyrrolidone), that perform selective complexation of the ion that is being concentrated according to the solution pH. The addition of a soluble polymer to the sample enables a more effective retention of the species intended by means of sample ultrafiltration. Although this automatization procedure is much more expensive than continuous-flow techniques, the polymers used are rather cheap when compared to the resins similarly employed in continuous flows.The present work reports on the behavior of poly-(vinylpyrrolidone) when used for the preconcentration of lead in the heterogeneous stage and continuous-flow conditions. Hence, the coupling of an analytical unit to a simple sequential injection analysis system has been studied and is being proposed. It is common knowledge that sequential injection analysis is a third-generation flow technique 13 characterized by being more robust and versatile regarding the variation of the analytical conditions. Therefore, a preconcentration procedure based on easily implemented analytical columns may be very advantageous, because the feeble optimization of the columns can be overcome by the hydrodynamic conditions featured by the SIA systems. Experimental Reagents and solutionsAll solutions were prepared with bideionized water (conductivity <0.1 µS/cm) and analytical-grade reagents without any further treatments.Lead calibrating solutions were prepared by dilution with water from a stock solution of 1 g/l lead previously prepared with Pb(NO 3 ) 2 . The pH of the calibrating solutions was set to the average level attained from the samples (pH=3) by adding 2 mol/l HNO 3 .For the interference assays, lead calibrating solutions with different concentrations of the interferent were prepared from stock solutions of 1 g/l previously attained by weighing and diluting the following substances: Faculdade de Farmácia (U.P.), Rua Anibal ...

A review on sequential injection methods for water analysis

“…Most of the works that include preconcentration and/or separation of the analyte refer to coupling SI methodology with ICP [50,51,58,102] and AAS [38,39,41,47,48,56,72,73,90,99,100,113,114,126,129,143]. The combination of SIA with ICP or AAS associates the advantages of SIA such as versatility, robustness and automation (useful for handling reagent and sample preparation) with selectivity and sensitivity of those detection methods.…”

“…Metals such as copper [ [50,51,58,102] and AAS [41,47,48,88,99,100,126,129] because these metals are found at very low concentrations in waters. In fact, there was only one spectrophotometric method described for cadmium [83], two for lead [81,82] and four for copper [59,74,92,130] as spectrophotometric determinations normally imply higher detection limits.…”

Flame Atomic Absorption Spectrometric Determination of Trace Quantities of Cadmium from Water Samples

“…Several spectral and electrochemical methods have been developed for determination of heavy metal ions [5][6][7][8][9][10][11]. Among the spectral methods, flame atomic absorption spectrometry (FAAS) is a more frequently used technique due to its simplicity and lower cost, although this method has a limited sensitivity for cadmium so a preconcentration step is often required to improve the detection limit [12][13][14]. Hence, combining a preconcentration step prior to FAAS determination is often resorted by various researchers.…”

A flow system for the spectrophotometric determination of lead in different types of waters using ion-exchange for pre-concentration and elimination of interferences

“…To automate the lead determination in water samples, different flow analysis concepts coupled to different detection systems have been described. With FAAS, a sequential injection system with lead pre-concentration in a polymer (poly(vinylpyrrolidone)) was presented [3], achieving a detection limit of 5 g l −1 . With ICP-AES, a flow injection [4] and a multicommutation [5] system involving a pre-concentration step were described; detection limits of 0.2 and 2 g l −1 , respectively, were obtained.…”