Metal ion preconcentration

Figure 4.14 — (A) Flow injection system for the preconcentration and determination of copper P peristaltic pumps A 0.5 M HNOj B sample q = 2.5 mL/min) C water (jq = 0.5 mL/min) E 1 M NaNOj/O.l M NaAcO, pH 5.4 q = 0.5 mL/min F 1 M NaAcO/2 x 10 M Cu pH 5.0 (9 = 1.0 mL/min) 3-5 valves ISE copper ion-selective electrode W waste I and II 2 and 3 mL of chelating ion exchanger for purification III 100 fil of chelating ion exchanger for metal ion preconcentration. (B) Scheme of the flow system for the determination of halides A 4 M HAcO/1 M NaCl/0.57 ppm F B 1 M NaOH/0.5 M NaCl C, mixing coil (1 m x 0.5 mm ID PTFE tube) Cj stainless-steel tube (5 cm x 0.5 mm ID) ISE ion-selective electrode R recorder. (Reproduced from [128] and [129] with permission of Elsevier Science Publishers and the Royal Society of Chemistry, respectively).

Stabilized liquid membrane device (SLMD) A water-insoluble organic complexing mixture diffuses to the exterior surface of the sampler through a polymeric membrane Divalent metal ions Preconcentration, in situ sampling, determination of labile metal ions in grab samples Days to several weeks Extraction with acid 73... 

Anodic stripping voltammetry is the most sensitive technique available for the determination of some metals in water samples [77]. Trace metal ions, preconcentrated on to the electrode surface by reduction, are analysed by taking the electrode positive after a selected deposition time. The charge passed in the resulting current (stripping) peak gives a measure of the... 

M. Bengtsson, F. Malamas, A. Torstensson, O. Regnell, and G. Johansson, Trace Metal Ion Preconcentration for Flame Atomic Absorption by an Immobilized N,N,N -Tri-(2-Pyridylmethyl)ethylene Diamine (TriPEN) Chelate Ion Exchanger in a Flow Injection Analysis. Mikrochim. Acta, III (1985) 209. 

Mandil A, Idrissi L, Amine A (2010) Stripping voltammetric dettmninatimi of mercury (II) and lead (II) using screen-printed electrodes modified with gold films, and metal ion preconcentration with thiol-modified magnetic particles. Microchim Acta 170 299—305... 

Martins, AO Silva, EL Carasek, E. Sulphoxine immobilized onto chitosan microspheres by spray drying application for metal ions preconcentration by flow injection analysis. Talanta, 2004, 63, 397-403. 

Ion Removal and Metal Oxide Electrodes. The ethylenediamine ( )-functional silane, shown in Table 3 (No. 5), has been studied extensively as a sdylating agent on siUca gel to preconcentrate polyvalent anions and cations from dilute aqueous solutions (26,27). Numerous other chelate-functional silanes have been immobilized on siUca gel, controUed-pore glass, and fiber glass for removal of metal ions from solution (28,29). 

Recent publications indicate the cloud-point extraction by phases of nonionic surfactant as an effective procedure for preconcentrating and separation of metal ions, organic pollutants and biologically active compounds. The effectiveness of the cloud-point extraction is due to its high selectivity and the possibility to obtain high coefficients of absolute preconcentrating while analyzing small volumes of the sample. Besides, the cloud-point extraction with non-ionic surfactants insures the low-cost, simple and accurate analytic procedures. 

Effective metal ion adsorbent has been prepai ed by the immobilization of propylthioethyleamine ligand onto the surface of silica gel (SN-SiO,).The effectiveness of this material to bind metal ions has been attributed to the complexation chemistry between the ligand and the metal. We are investigating properties of propylthioethyleamine grafted on the surface of silica and possibility of application of the obtained surface for preconcentration of heavy metals such as zinc, lead, cadmium, copper, etc. from water solutions. 

The capacity factors of SN-SiO, for metal ions were determined under a range of different conditions of pH, metal ions concentrations and time of interaction. Preconcentration of Cd ", Pb ", Zn " and CvS were used for their preliminary determination by flame atomic absorption spectroscopy. The optimum pH values for quantitative soi ption ai e 5.8, 6.2, 6.5, 7.0 for Pb, Cu, Cd and Zn, respectively. The sorption ability of SN-SiO, to metal ions decrease in line Pb>Cu> >Zn>Cd. The soi ption capacity of the sorbent is 2.7,7.19,11.12,28.49 mg-g Hor Cd, Zn, Pb, andCu, respectively. The sorbent distribution coefficient calculated from soi ption isotherms was 10 ml-g for studied cations. All these metal ions can be desorbed with 5 ml of O.lmole-k HCl (sorbent recovery average out 96-100%). 

On the basis of data obtained the possibility of substrates distribution and their D-values prediction using the regressions which consider the hydrophobicity and stmcture of amines was investigated. The hydrophobicity of amines was estimated by the distribution coefficient value in the water-octanole system (Ig P). The molecular structure of aromatic amines was characterized by the first-order molecular connectivity indexes ( x)- H was shown the independent and cooperative influence of the Ig P and parameters of amines on their distribution. Evidently, this fact demonstrates the host-guest phenomenon which is inherent to the organized media. The obtained in the research data were used for optimization of the conditions of micellar-extraction preconcentrating of metal ions with amines into the NS-rich phase with the following determination by atomic-absorption method. 

Essentially, stripping analysis is a two-step technique. The first, or deposition, step involves die electrolytic deposition of a small portion of the metal ions hi solution into die mercury electrode to preconcentrate the metals. This is followed by die shipping step (the measurement step), which involves die dissolution (shipping) of die deposit. Different versions of stripping analysis can be employed, depending upon die nature of the deposition and measurement steps. 

Since different metals strip from mercury electrodes at characteristic peak potentials, several metal ions can be determined simultaneously. Metal ions which have been determined by ASV at a mercury electrode are BP, Cd, Cu, Ga, Ge, In, NP, Pb, Sb, Sn, Tl, and Zn. Solid electrodes such as graphite enable Hg, Au, Ag, and PP to be determined by ASV. In this case, the metal is preconcentrated on the surface of the electrode as a metallic film, which is then stripped off by the positive potential scan. 

Horwitz EP, Chiarizia R, Dietz ML, Diamond H, Nelson DM (1993a) Separation and preconcentration of actinides from acidic media by extraction chromatography. Anal Chim Acta 281 361-372 Horwitz EP, Chiarizia, R., Diamond H, Gatrone RC, Alexandratos SD, Trochimzuk AQ, Crick DW (1993b) Uptake of metal ions by a new chelating ion exchange resin. 1. Acid dependencies of actinide ions. Solvent Extr Ion Exch 11 943-966... 

A logical approach which serves to minimise such uncertainties is the use of a number of distinctly different analytical methods for the determination of each analyte wherein none of the methods would be expected to suffer identical interferences. In this manner, any correspondence observed between the results of different methods implies that a reliable estimate of the true value for the analyte concentration in the sample has been obtained. To this end Sturgeon et al. [21] carried out the analysis of coastal seawater for the above elements using isotope dilution spark source mass spectrometry. GFA-AS, and ICP-ES following trace metal separation-preconcentration (using ion exchange and chelation-solvent extraction), and direct analysis by GFA-AS. These workers discuss analytical advantages inherent in such an approach. 

Horwitz, E. P. Shulz, W. W. Metal Ion Separation and Preconcentration Progress and Opportunities Bond, A. H. Dietz, M. L. Rogers, R. D. Eds., American Chemical Society, 1998. 

The use of impregnated resins in the preconcentration and separation of trace metal ions provides the following advantages ... 

Metal ions such Cu, Cd, and Pb can be preconcentrated from water samples using liquid membranes containing 40% w/w of di-2-ethylhexylphosphoric acid in kerosene diluent in a PTFE support. The liquid membrane can be coupled on-line to an atomic absorption spectrometer and has been shown to be stable for at least 200 h with extraction efficiencies over 80%, and enrichment factors of 15 can be obtained. A liquid membrane has also been used for sample cleanup and enrichment of lead in urine samples prior to determination by atomic absorption spectrometry [100]. The experimental setup for metal enrichment is shown in Fig. 13.4. Lead was enriched 200 times from urine [80] and several metals were enriched 200 times from natural waters [88]. Using hollow fiber... 

Cloud point extraction has been applied to the separation and preconcentration of analytes including metal ions, pesticides, fungicides, and proteins from different matrices prior to the determination of the analyte by techniques such as atomic absorption, gas chromatography, high performance liquid chromatography, capillary zone electrophoresis, etc. 

Extraction can be nsed for separation or isolation of the analyte from the sample matrix or vice versa as well as a preconcentration method. Extraction of metal ions is based on the reaction of weak organic acids with metal ions that give nncharged complexes that are highly solnble in organic solvents as ethers, hydrocarbons, ketones and polychlorinated species (generally chloroform and carbon tetrachloride). The efficacy of the extraction is mainly dependent on the extent to which solntes distribnte themselves between two immiscible solvents. The amonnts of analyte can be determined spectrophotometrically as well as with other available analytical methods. 

The construction and behavior of a mixed binder carbon paste electrode containing dimethylglyoxime have been described [79]. Such an electrode was used for CSV determination of mercury(II) and other metal ions. They were accumulated at the electrode surface during preconcentration step and later reduced from their complexes in the cathodic step. 

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