Preconcentration of metals

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. 

Preconcentration of metal cations is also achieved by providing ligand binding sites in polymer layers, e.g. 4-methyl-4 -vinyl-2,2 -bipyridine for Fe " and Cu ". Carbon paste electrodes containing dimethylglyoxime or o-phenanthroline... 

Matthews and Riley [336] determined indium in seawater at concentrations down to 1 ng/1. Preconcentration of metals on a cation exchanger was fol-... 

Chlorosilanes and alkoxysilanes commonly used in the modification of silica, with formula, acronym and common application with silica, (res. research, block. blocking agent, chrom. chromatography, comp. composites, enz. enzyme immobilization, IC integrated circuits, cat. catalyst, met preconcentration of metals). 

B. S. Garg, R. K. Sharma, J. S. Bist, N. Bhojak, S. Mittal, Separation and preconcentration of metal ions and their estimation in vitamin, steel and milk samples using o-vanil I in-immobilized silica gel, Talanta, 48 (1999), 49-55. 

Preconcentration of metals from water samples prior to atomic absorption spectrophotometric analysis increases the sensitivity of the analytical technique. It is only necessary when the level of metal required to be determined in the unconcentrated sample is below that which can be confidently measured by direct aspiration. 

OHLM techniques were used in analytical methods for separation and preconcentration of metals [252-254], organic acids [255,256], and organic and pharmaceutical compounds [257-261]. Preparation of the samples for analytical purposes seems to be one of the perspective directions in application of the OHLM processes. 

Zhang Li., Zhe-Ming N. and Xiao-Quan S. (1989) In situ preconcentration of metallic hydrides in a graphite furnace coated with palladium, Spectrochim Acta, Part B 44 339-346. 

In the last two decades, BOHLM techniques were intensively used in analytical chemistry for separation and preconcentration of metals, organic acids, organic, and pharmaceutical compounds. Some membrane-based... 

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 4.40. (a) Manifold and b) microconduit incorporating an ion-exchange column as used for preconcentration of metal ions. The sample, injected into the carrier stream C, is mixed with buffer B to adjust pH before entering the column filled with Chelex-IOO (volume 150 (xL). Metal ions are retained on the column and are subsequently eluted countercurrently by a small zone of eluent (E, acid) pumped by pump P2. As the two pumps are operated sequentially, the eluted sample is carried to detector D (atomic absorption spectrophotom-. eter). The manifold components within the boxed area are those contained within the microconduit. 

The preconcentration of metals by electrodeposition onto a tantalum strip for flameless AAS has not been described and though similar to the wire-loop atomizer, the greater stability and malleability attainable with tantalum should make it possible to extend the method more readily to other metals. In fact, the... 

Preconcentration of metal ions from ethanolic solution by a packing material based on silica gel functionalized with 3-(l-imidazolyl) propyl groups for column chromatographic application was performed. The modified silica gel was applied to preconcentrate Cu, Ni, Fe, Zn, and Cd ions from commercial ethanol. The method is suitable for quantitative determination of these metals at low JLg/L levels. 

Moriera, J.C. Gushikem, Y. Preconcentration of metal ions on silica gel modified with 3(l-imidazolyl)propyl groups. Anal. Chim. Acta 1985, 176, 263. 

M. Haratake, K. Yasumoto, M. Qno, M. Akashi, and M. Nakayama. S)mthesis of hydrophilic macroporous chelating polymers and their versatility in the preconcentration of metals in seawater samples. Analytica Chimica Acta 561 183-190,2006. 

In 1952, G. C. Barker and I. L. Jenkins were the first who have shown that a reductive preconcentration of metals at a mercury electrode gives the possibility to decrease the detection limit of analytical determinations [17]. Although they have understood the potential of this approach, they did not realize its real value, as they... 

---