SEPARATION AND PRE-CONCENTRATION

All main aspects of analytical and bioanalytical sciences is covered by the conference program. AC CA-05 consists of 12 invited lectures and seven symposia General Aspects of Analytical Chemistry, Analytical Methods, Objects of the Analysis,. Sensors and Tests, Separation and Pre-concentration, Pharmaceutical and Biomedical Analysis, History and Methodology of Analytical Chemistry. Conference program includes two special symposia Memorial one, dedicated to Anatoly Babko and Analytical Russian-Germany-Ukrainian symposium (ARGUS-9). 

Application of rotating coiled columns has become attractive for preparative-scale separations of various substances from different samples (natural products, food and environmental samples) due to advantages over traditional liquid-liquid extraction methods and other chromatographic techniques. The studies mainly made during the last fifteen years have shown that using rotating coiled columns is also promising for analytical chemistry, particularly for the extraction, separation and pre-concentration of substances to be determined (analytes) before their on-line or off-line analysis by different determination techniques. 

Zhu Z, Fang Z. 1987. Spectrophotometric determination of total cyanide in waste waters in a flow-injection system with gas-diffusion separation and pre-concentration. Anal Chim Acta 198 25-36. 

The application of analytical methods to speciation measurements in complicated systems has remained rather limited, despite the considerable technological progress during the past 25 years. The characterisation methods (e.g. spectroscopy, nuclear magnetic resonance) are often limited to the study of isolated compounds at relatively high concentrations. They, therefore, necessitate the prior employment of sophisticated separation and pre-concentration methods which introduce severe risks of perturbation. The trace analysis methods are often insensitive to the chemical form of the elements measured (e.g. atomic absorption, neutron activation). Those which possess sufficient element specificity (e.g. electron spin resonance, fluorescence, voltammetry) still require significant development before their full potential can be realised. 

Bezerra, M.A., Arruda, M.A.Z., Ferreira, S.L.C. Cloud point extraction as a procedure of separation and pre-concentration for metal determination using spectroanalytical techniques a review. Appl. Spectrosc. Rev. 40, 269-299 (2005)... 

Meeravali, N.N., Kumar, S.J., Jiang, S.J. An acid induced mixed-micelle mediated cloud point extraction for the separation and pre-concentration of platinum from road dust and determination by inductively coupled plasma mass spectrometry. Anal. Methods 2, 1101-1105 (2010)... 

Three methods are reported to quantify these TFSV-thiols analytes with separation and pre-concentration steps (Tominaga et al., 1998c Schneider et al., 2003 Mateo-Vivaracho et al., 2007). For all such approaches, the first step of the analysis is their recovery from... 

By using ion-exchange resins, a selected metal ion can be isolated (separated) and pre-concentrated from its matrix. This process can be carried out in two ways, i.e. by (i) batch, or (ii) column processes. In the batch process, the ion-exchange resin is added to the aqueous sample, whereas in the second process the resin is packed into a chromatographic column. The former would be always carried out off-line, while the latter could be carried out in either on-line or off-line mode. 

O. Bakajin, Micro-separation and pre-concentration columns based on carbon nanotube arrays, DARPA-MTO webpage, 2004, at http //www.darpa.mil/ mto/mga/summaries/2004 summaries/ llnl.html... 

Separation and pre-concentration of the sample is frequently carried out before attempting quantitative estimation. This may facilitate the removal of interfering elements such as As, Si, etc., which might otherwise be obtained as isostructural compounds in the analytical process. 

R. Rodriguez, J. Avivar, L. Ferrer, L.O. Leal, V. Cerda, Automated total and radioactive strontium separation and pre-concentration in samples of environmental interest exploiting a lab-on-valve system, Talanta 96 (2012) 96-101. 

Separation and pre-concentration. A method first suggested by Knapp et al. (1975), developed further by Prange (1983) for seawater analysis using TXRF and later slightly modified by Schmidt et al. (1993) combines matrix removal with enrichment by a factor of about 50. The elements V, Mn, Fe, Co, Ni, Cu, Zn, Se, Mo, Cd, Pb and U are chelated using sodium-dibenzyldithiocarbamate (Na-DBDTC). The water-insoluble chelates are adsorbed on a column of a reversed-phase silica gel. Alkaline and alkaline earth elements elute unchelated with the aqueous phase and are discarded. The chelate complexes are removed from the dried column with a mixture of chloroform and methanol (methanol is needed for the quantitative elution of Mo). Some 100/tL of this extract are evaporated on quartz sample carriers and measured for around 1000 s. 

Fang Z. (1993) Flow Injection Separation and Pre-concentration, VCH, Weinheim. 

Dressier, V. L., Pozebon, D., and Curtins, A. J. (1998). Determination of heavy metals by inductively coupled plasma mass spectrometry after on-line separation and pre- concentration. Spectrochim.Acta, Part B 53(11), 1527. 

Pre-concentration methods using online trace enrichment by applying chromatographic principles are also reported [66,69]. As described by Guzman and Meyers [71,72], this can be achieved by incorporating e.g. a solid-phase CE-concentrator tip at the inlet of the capillary. Undesired sample components can be flushed out prior to the CE separation run, providing faster and more specific analyses. Especially in the field of bioanalysis, where sample clean up and pre-concentration of analytes is usually critical, this approach may be preferred. 

FIGURE 5.10 Side-view schematic of miniaturized affinity dialysis and pre-concentration system. I, II, and III indicate top, middle, and bottom imprinted copolyester pieces, respectively. Piece II is imprinted on both sides. Two PVDF membranes separate the copolyester channels [821]. Reprinted with permission from the American Chemical Society... 

Membrane separation technology is well developed in the dairy industry. In particular, the largest applications are related to the use of UF in the fractionation of cheese whey and pre-concentration of milk for cheese manufacture. RO is mainly used for whey concentration and the membrane area has stabilized around 60 000 m (Daufin et al., 2001). MF is able to retain, partially or totally, particles such as microorganisms, casein micelles and fat globules providing longer shelf life than pasteurization. It can be used as pre-treatment of skim nfilk for the production of raw milk cheeses and the reduction of spores in add cheese milk. NF, due to its intermediate... 

Excellent examples of the determination of ultra-trace levels are provided by the analysis of in environmental and biological samples. The short-lived 1 is produced in the (n,y) reaction and is easily detected by gamma-ray spectrometry, while the stable 1 undergoes the (n,2n) reaction-forming I that can be used to monitor the chemical recovery. Recovery can also be monitored with radiotracers, e.g., 1 and 1. To achieve the highest sensitivity, postirradiation radiochemical separation and pre-irradiation chemical concentration are also applied. 

The advantages of hyphenation of CE to SIA over stand-alone CE instruments are that (a) the separation electrolyte and the sample are continuously replenished in the interface (b) the samples that are injected in the CE system are introduced into the separation capillary without the need to interrupt the separation voltage or to physically move the separation capillary (c) repeated injections of samples can be made independently during the progress of the separation process inside the CE capillary and (d) sample treatment (such as filtration, dilution, membrane-based separations, derivatization, pre-concentration, etc., can be effectively carried out in the SIA part of the manifold during the separation of the previous sample in the CE instrument (Kuban and Karlberg, 2009). 

In a flow injection system, the sample flow and a reagent flow are continuously brought together so as to allow a chemical reaction to take place. This reaction produces a gaseous compound, which has to be separated off as in hydride generation, or forms a complex, which can be adsorbed onto a solid phase to be isolated and pre-concentrated. In the latter case, elution with a suitable solvent is carried out and the analytes are led on-line into the AAS system. 

Posta j., Beendt H., Luo S. K. and Schaldach G. (1993) High-performance flow flame atomic absorption spectrometry for automated on-line separation and determination of Cr(III)/Cr(Vl) and pre-concentration of Cr(VI), Anal. Chem. 65 2590-2595. 

Nd isotopic composition measrrrement of seawater is difficult. Difficulties arise from the need to collect high-precision Nd isotope ratios on samples with only a small amount of Nd (approximately 2 ng per kg of seawater vs. 40 xg Nd per gram of continental crust). Typically, the lanthanides are extracted and pre-concentrated from 10-30 kg samples of seawater, and Nd is separated from its neighbors. The Nd/ Nd ratio is measured by thermal ionization mass spectrometry (e.g., Piepgras et al. 1979, Piepgras and Jacobsen 1988, Bertram and Elderfield 1993). 

J. H. Beattie, R. Self and M. P. Richards, The use of solid phase concenti ators for online pre-concentration of metallothionein prior to isofom separation by capillary zone electrophoresis , Electrophoresis 16 322-328 (1995). 

Completion of the analysis. The technique of solvent extraction permits the separation and often the pre-concentration of a particular element or substance (or of a group of elements or substances). Following this separation procedure, the final step of the analysis involves the quantitative determination of the species of interest by an appropriate technique. 

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