Separations preconcentration

No preconcentration or isolation/separation procedures applied Physico-chemical separation/preconcentration Hydride generation, cold vapor generation (Hg)... 

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. 

Flow injection analysis is based on the injection of a liquid sample into a continuously flowing liquid carrier stream, where it is usually made to react to give reaction products that may be detected. FIA offers the possibility in an on-line manifold of sample handling including separation, preconcentration, masking and color reaction, and even microwave dissolution, all of which can be readily automated. The most common advantages of FIA include reduced manpower cost of laboratory operations, increased sample throughput, improved precision of results, reduced sample volumes, and the elimination of many interferences. Fully automated flow injection analysers are based on spectrophotometric detection but are readily adapted as sample preparation units for atomic spectrometric techniques. Flow injection as a sample introduction technique has been discussed previously, whereas here its full potential is briefly surveyed. In addition to a few books on FIA [168,169], several critical reviews of FIA methods for FAAS, GF AAS, and ICP-AES methods have been published [170,171]. 

To determine ions at mid pg/1 to mg/1 (ppb to ppm) levels with IC, a sample size of 10 to 50/pi is sufficient. To determine ions at lower levels, then a preconcentration or trace enrichment technique has t3rpically to be utilized [20]. With this method, the analytes of interest are preconcentrated on another column in order to "strip" ions from a measured sample volume. This process concentrates the desired species resulting in lower detection limits. However, preconcentration has several disadvantages, compared with a direct method, additional hardware is required. A concentrator column is used to preconcentrate the ions of interest, a sample pump is needed for loading sample, an additional valve is often required for switching the concentrator column in and out-of line with the analytical column and extra time is required for the preconcentration step. It was of interest to explore the development of a high-volume direct-injection IC method that would facilitate trace ion determinations without a separate preconcentration step. This would represent a significantly simpler and more reliable means of trace analysis. 

Flow systems are developed mainly for liquid samples and their complexity can range from simple to very complex manifolds to deal with ultratrace amounts of the target analyte in complex matrices, which often require on-line separation/preconcentration steps. As a wide variety of chemical manipulations can be carried out in an FI manifold, the scope of the FI applications is enormous. Not only liquid samples, but also both gas and solid samples, can be also introduced into the liquid flow manifold if special adaptations are made. Gas samples simply require impermeable tubing. Solids can be either introduced into the system and leached with the help of auxiliary energy e.g. ultrasound) or introduced as slurries. 

Liang, P., T.Q. Shi, and J. Li. 2004. Nanometer-size titanium dioxide separation/preconcentration and FAAS determination of trace Zn and Cd in water sample. Int. J. Environ. Anal. Chem. 84 315-321. 

Z. Marczenko and M. Balcerzak, Separation, Preconcentration and Spectrophotometry in Inorganic Analysis , Translated... 

In some situations, an apparent decrease in the detection limit can occur when the analytical procedure includes a preliminary preconcentration (e.g., by extraction or evaporation of a liquid sample). For example, if direct determination by atomic absorption spectrometry allows detection of 0.1 ng/mL metal in solution, then an increase in concentration after separation/preconcentration in the ratio 1 20 lowers the detection limit for the whole procedure to 0.005 ng/mL. Both values are useful and have real meaning when they are correctly described. 

Bosch, O.C., Sanchez, R.F., Cano, P.J., Garcia de Torres, A. Automated on-line separation-preconcentration system for platinum determination by electrothermal atomic absorption spectrometry. Anal. Chlm. Acta 494, 97-103 (2003)... 

Accelerated solvent extraction as implemented in commercial equipment is basically discrete in nature, so it is rarely coupled to other operations of the analytical process. In fact, only in two reported applications was the static mode coupled on-line to other operations such as chromatographic separation, preconcentration and detection. Both used custom extractors as the compact design of the commercial models precluded their adaptation. 

Countercurrent chromatography has been mainly developed and used for preparative and analytical separations of organic and bio-organic substances [1], The studies of the last several years have shown that the technique can be apphed to analytical and radiochemical separation, preconcentration, and purification of inorganic substances in solutions on a laboratory scale by the use of various two-phase liquid systems [2], Success in CCC separation depends on choosing a two-phase solvent system that provides the proper partition coefficient values for the compounds to be separated and satisfactory retention of the stationary phase. The number of potentially suitable CCC solvent systems can be so great that it may be difficult to select the most proper one. 

Part II, devoted to individual chemical elements, describes the methods for separation, preconcentration, and spectrophotometric determination of the elements, as well as the application of these methods in the analysis of materials. The detailed discussion comprises the theory, preparation of standard solutions, and analytical procedures. 

The use of a separation, preconcentration and measuring procedure depends to a great extent on the species that is to be determined (Lund, 1990 Baeyens, 1992 Szpunar-Lobinska et al., 1995 Mendez Garcia et al., 1996 Buffle et al., 1997). 

Separation, Preconcentration and Speciation of Organic Phosphorus in Environmental Samples... 

Very limited laboratory bench space and utensils required. Excluding the detector, sometimes a FI on-line separation/preconcentration system occupies no more space than an electronic typewriter. 

Bartseh, RA. Metal ion separations with proton-ionizable lariat ethers. ACS Symp. Ser. Metal-Ion Separ. Preconcentration 1999, 716, 146-155. 

EDCs in the aquatic environment are often present in complex matrices such as effluent samples. For this reason, wide ranges of sample preparation and preconcentration techniques have been employed in conjunction with analytical separations. Preconcentration is often necessary due to sensitivity limitations of the instrumental techniques. 

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