Lead preconcentration procedure

Although ICP-ES is a multielement technique, its inferior detection limits (relative to GFA-AS) necessitate the processing of relatively large volumes of seawater. 250 mL aliquots were found to be useful for the analysis of iron, manganese, zinc, copper, and nickel. Extension of the method to include cadmium, cobalt, chromium, and lead would require improvements in the preconcentration procedure. 

Three methods for trace metal preconcentration were examined liquid-liquid extraction aided by a chelating agent, concentration on a synthetic chelating resin and reductive precipitation with NaBTLt. The latter method gave 1000-fold preconcentration factors with total recovery of Pb and other elements17. Preconcentration of nanogram amounts of lead can be carried out with a resin incorporating quinolin-8-ol (3)18. Enhancement factors of 50-100 can be achieved by such preconcentration procedures followed by determination in a FLA (flow injection analysis) system limits of detection are a few pg Pb/L19. 

M. Soylak, I. Narin, M. Almeida Becerra and S. L. Costa Ferreira, Factorial design in the optimisation of preconcentration procedure for lead determination by FAAS, Talanta, 65(4), 2005, 895-899. 

A study of mercury in Lake Michigan found levels near 1.6 pM (1.6 X 10 12 M), which is two orders of magnitude below concentrations observed in many earlier studies.5 Previous investigators apparently unknowingly contaminated their samples. A study of handling techniques for the analysis of lead in rivers investigated variations in sample collection, sample containers, protection during transportation from the field to the lab, filtration techniques, chemical preservatives, and preconcentration procedures.6 Each individual step that deviated from best practice doubled the apparent concentration of lead in stream water. Clean rooms with filtered air supplies are essential in trace analysis. Even with the best precautions, the precision of trace analysis becomes poorer as the concentration of analyte decreases (Box 5-2). 

FAAS is the oldest version of AAS. It works with liquid samples which after nebu-lization are mixed with acetylene and introduced in a flame atomizer burner with air-acetylene or N20-acetylene flame. A single measurement can be completed within 10 s. Theoretically the method is applicable to 60-70 elements and due to its low cost, selectivity and simple operation is preferred whenever the concentration of the determined elements is within its possibilities. The sensitivity of FAAS is of the same order of magnitude as of ICP-AES and for some elements even worse which in recent years has lead to the replacement of FAAS with the multielement ICP-AES. To increase the sensitivity of FAAS usually preconcentration procedures are applied before measurement. Otherwise FAAS permits direct measurements in the low mg/kg range of a number of metals in soils and sediments, six to ten elements in plants and in natural waters. It is sensitive enough for the direct determination of Al., Ba, Ca, Cu, Fe, K, Na, Mg, Mn and Zn in different environmental materials (alkaline metals are determined by flame atomic emission spectrometry). Due to the narrow dynamic range problems with the accuracy appear (e.g. Djingova et al., 1991) and very often dilutions are necessary which decreases relative sensitivity and increases the possibilities for errors. 

W. N. L. dos Santos, J. V. S. Santos, L. O. B. Laiana, A. S. Araujo, V. A. Lemos, M. Miro and S. L. C. Ferreira, On-line simultaneous preconcentration procedure for the determination of cadmium and lead in drinking water employing sequential multi-element flame atomic absorption spectrometry, Int. J. Environ. Anal. Chem., 2011, 91(15), 1425-1435. 

We will present the basics of the simplex method with the aid of a simulation and then describe the algorithm. As an example, Soylak et al. [18] optimised a procedure to preconcentrate lead (the studied response, Y) using a 2 factorial design in which the factors were ... 

As regards fractionation methodologies for the selective determination of Pb and other metals compounds in wines, Lemos et al. [57] have developed a FIA method for the direct determination of available free Pb(II) and total Pb content in wine samples. Lead (II) was chemically retained on a packed polyurethane foam microcolumn, modified by immobilization of 2-(2-benzothiazolyazo)p-cresol (BTAC) and eluted with 0.1 M HC1. The eluate was determined on-line by FAAS. Total Pb was quantified after sample digestion with HN03 and H202, whereas free Pb was determined by direct sample on-line preconcentration and elution. No effect of ethanol on the enrichment procedures was observed. With a preconcentration factor of 26 an LoD of 1 xg l-1 was reached. Four red and three white wines of different origins were analyzed and the total Pb content varied from 8 to 42 p,g 1 1. 

The use of GC-MIP-AES is advantageous because it avoids the predecomposition step required in the AAS detection mode. The first applications of the MIP-AES detector for Hg speciation and detection were reported in the 1970s [27-29]. Despite the overall good detection ability of the detectors, however, most of the above methods require large sample volumes, tedious solvent extraction procedures, and usually lead to the final determination of only the Me-Hg species. The description of the feasibility of quantitative in situ aqueous ethylation of Hg2-1- and Me-Hg followed by on-line preconcentration and detection by atomic fluorescences pectro-metry (AFS) or AAS certainly produces a wealth of information since it allows all Hg species to be detected in the same chromatographic run. Also on-line speciation of Hg and Me-Hg by chromatography-AFS hydride generation (HG) was used [30]. 

The Co-APDC co-precipitation procedure for preconcentration has been shown to be suitable for the determination of lead in freshwater samples. Cadmium determination at concentrations ca. 0.1 mg l-1 in freshwater can also be performed using this procedure at lower concentrations an... 

FI manifolds for column separation and preconcentration in spectrophotometry are diverse, and there is hardly one which may be considered typical. However, the reader may refer to the manifold used in the determination of boron just mentioned (63]. Another interesting contribution by Novikov et al.[ll] combined ion-exchange column preconcentration with on-line solvent extraction followed by spectrophotometric detection. The eluate from the column preconcentration was released into an on-line liquid-liquid extraction system. An advantage of this approach is that interferences from Schlieren effects are avoided, since the eluate does not flow directly to the detector. Selectivity and sensitivity are also enhanced due to the combination of two separation procedures. The system has been used successfully for the determination of lead in alloys, soil leachates and sea water. 

This review considers the literature of the past years (up to 1979) that treats the preconcentration of the priority pollution metals antimony, arsenic, beryllium, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, thallium, and zinc. In some cases, a brief outline is given or some discussion of the method, but in most instances, the number of methods available precludes more than a mention of their specific application or special feature. For some elements such as mercury many methods of preconcentration are available, for others such as beryllium and thallium only a few are reported. Relatively few procedures actually detail the analysis of a sample containing several species both organic and inorganic, although this area is of major concern, because of large differences in the relative toxicity of the various species. 

Fiydride generation (and cold-vapor) techniques significantly improve atomic absorption spectrometry (AAS) concentration detection limits while offering several advantages (1) separation of the analyte from the matrix is achieved which invariably leads to improved accuracy of determination (2) preconcentration is easily implemented (3) simple chemical speciation may be discerned in many cases and (4) the procedures are amenable to automation. Disadvantages with the approach that are frequently cited include interferences from concomitant elements (notably transition metals), pH effects, oxidation state influences (which may be advantageously used for speciation) and gas-phase atomization interferences (mutual effect from other hydrides). 

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