Trace metal preconcentration system

Although the automated, trace-metal preconcentration system has undergone a number of design changes, the major characteristics are summa-... 

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. 

Katarina, R.K., N. Lenghor, and S. Motomizu. 2007. On-line preconcentration method for the determination of trace metals in water samples using a fully automated pretreatment system coupled with ICP-AES. Anal. Sci. 23 343-350. 

Olsen et al. (48, 20) have described an interesting method for the determination of lead in polluted seawater using FIA and flame atomic absorption spectroscopy. The system incorporates a Chelex-100 column for on-line preconcentration of the sample. The preconcentration and elution step improves the detection limit for lead by a factor of four (50 nM). Further increases in sensitivity are easily possible. The combination of this preconcentration step with a more sensitive detector, such as anodic stripping voltammetry, may make possible the determination of trace metals in seawater on a routine basis. 

C.R.T. Tarley, S.L.C. Ferreira, M.A.Z. Arruda, Use of modified rice husks as a natural solid adsorbent of trace metals characterisation and development of an on-line preconcentration system for cadmium and lead determination by FAAS, Microchem. J. 77 (2004) 163. 

Lipid-Bound Macrocycles as New Immobilized Ligand Systems for Effective Separation of Metal Cations (Tsukube et al., 1991) (5) Application of Macrocyclic Ligands to Ion Chromatography (Lamb and Smith, 1991) (6) Chromatographic Separation of Metal Cations on Silica Gel Chemically Modified with a Polymeric Diaza-18-crown-6 Derivative (Basyuk, 1991) and (7) Column Preconcentration of Trace Metals from Sea Water with Macroporous Resins Impregnated with Lipophilic Macrocycles (Blain et al., 1991). 

Ouinolin-8-ol immobilized on silica was used for on-line preconcentration purposes with an ICP-MS system [17]. Isotope dilution and standard addition methods were applied for the determination of trace metals in a sea water standard reference material. A similar ion-exchanger was used for on-line preconcentration of cobalt with catalytic sp>ectrophotometric determination [18]. 

A wide variety of inorganic materials have been used to precipitate or collect trace metals from solution. The most direct approach is a cementation process, which is one that removes the trace pollutants from solution by reduction with a metal and plating onto that metal surface. Although this process may be slow, the filtration is usually quick, since decantation is often sufficient. Finely divided cadmium extracts copper, selenium, and mercury from nitric and sulfuric acid solutions (66). When copper was used to preconcentrate mercury from water or biological fluids prior to atomic absorption analysis, the detection limit was 1-2 X 10 g (67, 68). Iron (69), zinc (70), and tungsten (71), as metals, have also been used to obtain a deposit of several trace metals from aqueous systems as dilute as 10 ppb for subsequent analysis. Elemental tellurium can be produced in solution by reduction using tin(II) chloride or sulfur dioxide, and coprecipitates silver (72) and selenium (73). Granulated silicon-metal alloys were used to remove metal ions from water and brine by reduction as well (74, 75). 

Solvent extraction is one of the most powerful methods of preconcentration of trace metals from aqueous systems. Some important books and reviews of the subject are available for a description of the theory as well as detailed conditions for the separation of individual metals (458-472). 

In this article we have attempted to review the many methods of preconcentration available for trace metals in aqueous systems. It was not possible to cover the many thousands of publications in this area which have resulted from the... 

Groschner, M. Appriou, P. Three-colunm system for preconcentration and speciation determination of trace metals in natural waters. Anal. Chim. Acta 1994, 297, 369. 

Nakashima, S. Sturgeon, R.E. Willie, S.N. Berman, S.S. Determination of trace metals in seawater by graphite furnace atomic absorption spectrometry with preconcentration on silica-immobilized 8-hydroxyquinoline in a flow-system. Fresenius Z. Anal. Chem. 1988, 330 (7), 592. 

G.M. Sawula. On-site preconcentration and trace metal ions determination in the Okavango Delta water system, Botswana. Talanta 64 80-86, 2004. 

Kumagai, H.,Yamanaka, M., Sakai,T., andYokoyama.T. (1998). Determination of trace metals in sea-water by inductively coupled plasma mass spectrometry interfaced with an ion chromatographic separation system Effectiveness of nitrilotriacetate chelating resin as the column stationary phase for preconcentration and elimination of matrix effects. Anal. At. Spectrom. 13(6), 579. 

Fang et al. [661] have described a flow injection system with online ion exchange preconcentration on dual columns for the determination of trace amounts of heavy metal at pg/1 and sub-pg/1 levels by flame atomic absorption spectrometry (Fig. 5.17). The degree of preconcentration ranges from a factor of 50 to 105 for different elements, at a sampling frequency of 60 samples per hour. The detection limits for copper, zinc, lead, and cadmium are 0.07, 0.03, 0.5, and 0.05 pg/1, respectively. Relative standard deviations are 1.2-3.2% at pg/1 levels. The behaviour of the various chelating exchangers used was studied with respect to their preconcentration characteristics, with special emphasis on interferences encountered in the analysis of seawater. 

Fig. 4.14 Flow-injection assemblies for ion-exchange preconcentration of metal traces prior to introduction into an atomic absorption spectrometer. (A) Single-line manifold (B) three-valve system for upstream elution (C) automated assembly with intermittent pumping. (Reproduced from [11] with permission of the Royal Society of Chemistry).

Figure 4.39. Single-line two-valve FIA system for on-line preconcentration as used for the determination of trace amounts of metal ions. A large sample volume is injected into the carrier stream by means of valve S and propelled into a small column containing a cation exchanger (Chelex-100), which effectively retains the metal ions. Hence no signal is recorded by the detector. Next, a small volume of eluent (E, nitric acid) is injected by the second valve, the metal ions on the column being eluted into a small zone that upon transport to the detector gives rise to a signal before the sample is led to waste, W.

Z. Fang, S. Xu, and S. Zhang, The Determination of Trace Amounts of Heavy Metals in Waters by a Flow-Injection System Including Ion-Exchange Preconcentration and Flame Atomic Absorption Spectrometric Detection. Anal. Chim. Acta, 164 (1984) 41. 

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