Extraction chromatographic separations

Today SCFs are used for natural product extractions, chromatographic separations, pollution prevention, material processing and as solvents for chemical reactions.[75-77] Chemical applications include catalysis, polymerization, enzymatic reactions and organic synthesis. 

For the IR spectroscopic identification of additives in polymeric products, in many cases it is necessary to first isolate the additive either by solvent extraction, chromatographic separation or removal of interfering constituents by ashing, etc. 

Zinnen, H.A. (1991) Extractive chromatographic separation process for recovering 3,5-diethyltoluene. U.S. Patent 5,019,271. 

For any pure chemical species, there exists a critical temperature (Tc) and pressure (Pc) immediately below which an equilibrium exists between the liquid and vapor phases (1). Above these critical points a two-phase system coalesces into a single phase referred to as a supercritical fluid. Supercritical fluids have received a great deal of attention in a number of important scientific fields. Interest is primarily a result of the ease with which the chemical potential of a supercritical fluid can be varied simply by adjustment of the system pressure. That is, one can cover an enormous range of, for example, diffusivities, viscosities, and dielectric constants while maintaining simultaneously the inherent chemical structure of the solvent (1-6). As a consequence of their unique solvating character, supercritical fluids have been used extensively for extractions, chromatographic separations, chemical reaction processes, and enhanced oil recovery (2-6). 

Method Validation The procedure by which an LC-MS method (extraction, chromatographic separation, and MS detection) developed for quantitative... 

Mathur, J.N. Murali, M.S. Iyer, R.H. Ramanujam, A. Dhami, P.S. Gopalkrishnan, V. Rao, M.K. Badheka, L.P. Baneiji, A. Extraction chromatographic separation of minor actinides from purex high-level wastes using CMPO, Nucl. Technol. 109 (1995) 216-225. 

Naik, P.W. Dhami, P.S. Misra, S.K. Jambunathan, U. Mathur, J.N. Use of organo-phosphorus extractants impregnated on silica gel for the extraction chromatographic separation of minor actinides from high level waste solutions, J. Radioanal. Nucl. Chem. 257 (2003) 327-332. 

By the late 1990s and into the 2000s, a number of additional groups became involved in automated fluidic separations for radiochemical analysis, especially as a front end for ICP-MS. Published journal articles on fluidic separations for radio-metric or mass spectrometric detection are summarized in Tables 9.1 through 9.5. The majority of such studies have used extraction chromatographic separations, and these will be the main focus of the remainder of this chapter. Section 9.4 describes methods that combine separation and detection. Section 9.5 describes a fully automated system that combines sample preparation, separation, and detection. 

Hollenbach et al. captured "Tc from standards or soil sample digestates on a TEVA-Resin column for on-line purification and preconcentration prior to ICP-MS determination.49 A wash solution of 0.5 M HN03 was used to remove interferences prior to elution with 8 M HN03 solution. A Re isotope, which behaves similarly to pertechnetate on TEVA-Resin, was used as an internal standard. Recoveries from the column varied from 97 to 99.5%, and columns could be reused over a hundred times. The use of the on-line column separation reduced detection limits by 10-fold and alleviated matrix and isobaric interferences compared to direct sample injection. This pioneering study adapted FIAS-200 and FIAS-400 FI systems to perform sample injection and extraction-chromatographic separations upstream from the ICP-MS. 

FIG U RE 9.4 Extraction chromatographic separation of "Tc(VII) from other fission products in the sample using a sequential injection separation system with a TEVA-Resin column. The signal for the "Tc is shown in the vertically expanded trace in the inset. (Reproduced from Egorov, O. B., O Hara, M. J., Ruzicka, J., and Grate, J. W., Anal. Chem., 70, 977-984, 1998. With permission.)... 

The largest number of automated extraction-chromatographic separations for actinides have used TRU-Resin, and many of these have coupled the column to ICP-MS as an on-line separation (see Table 9.3). TRU-Resin is impregnated with the neutral bifunctional organophosphorus complexant, octyl(phenyl)-A,A-diisobu-tylcarbamoylmethylphosphine oxide (CMPO) in tri-n-butyl phosphate (TBP).26 127 128 The organic stationary phase in this resin binds trivalent, tetravalent, and hexavalent actinide nitrato complexes from nitric acid solutions (see Figure 9.11). The extraction equilibria for representative species are shown in Equations 9.3-9.5, where the bar above a species indicates that it is immobilized on the resin.4... 

Sample preparation is required to cope with the sample matrix, the interferences, and the speciation of "Tc. The separation processes for isolating "Tc prior to radiometric detection require that the "Tc be in the pertechnetate ("TCO4) state. However, in waste samples with high organic content, much of the "Tc may be present in reduced valence states. Therefore, to determine the total "Tc content, all the "Tc must be oxidized to the pertechnetate state prior to ion-exchange or extraction-chromatographic separation. 

Grate, J. W., Egorov, O. B., and Fiskum, S. K., Automated extraction chromatographic separations of actinides using separation-optimized sequential injection techniques, Analyst, 124, 1143-1150, 1999. 

Kremliakova, N. Y., Novikov, A. P, and Myasoedov, B. F., Extraction chromatographic separation of radionuclides of strontium, cesium, and barium with the use of tvex-dchl8c6, J. Radioanal. Nucl. Chem. Lett., 145, 23-28, 1990. 

The separation components can provide for membrane separation, co-current or countercurrent flow extraction, chromatographic separation, electrophoretic... 

An internal standard is expected to track the analyte in all the three distinctive stages of LC-MS bioanalysis, i.e., sample preparation (extraction), chromatographic separation, and mass spectrometric detection. Though the emphasis should usually be... 

Wehner, H., ALMurab, S., Stoppler, M. Extraction-chromatographic separation of neptunium-239 from fission and activation products in the determination of microgram and submicrogram quantities of uranium. Radiochem. Radioanal. Lett. 13, (1973)... 

Analytes may be quantitated using an internal standard or by the method of standard addition. An internal standard is a structural analog (e.g. deuterium-labeled compound), a known amount of which is added to specimens prior to any preparatory steps such as extraction or hydrolysis. Ideally, the internal standard should be as chemically similar to the analyte of interest as possible, so that throughout the analytical procedure (e.g. extraction, chromatographic separation and ionization processes) and under the specified conditions (e.g. derivatization), its recovery will be similar to the analyte s. The concentration of analyte can then be determined from the ratio of the analyte response to the internal standard response. 

O.B. Egorov, M.J. O Hara, O.T. Farmer III, J.W. Grate, Extraction chromatographic separations and analysis of actinides using sequential injection techniques with online inductively coupled plasma mass spectrometry (ICP MS) detection, Analyst 126 (2001) 1594. 

Moegensteen a, Apostolidis, Carlos-Marques R, Mayer K and Molinet R (2002) Single-column extraction chromatographic separation ofU, Pu, Np and Am. Radiochim Acta 90 81—85. 

Solvent extraction, chromatographic separation, distillation and precipitation of heavy metals as sulphides are among the techniques employed for this purpose. Isobutyl acetate, for example, extracts molybdophosphate but not molybdosilicate at pH = 0.3-1.0. Butanol and chloroform can be used to separate molybdophosphate from molybdoarsenate. Under the appropriate circumstances. Si, As and Ge can be distilled off from the sample as volatile halides, and B removed as McjB. 

Vajda N, Toervenyi A, Kis-Benedek G, Kim CK (2009) Development of extraction chromatographic separation procedures for the simultaneous determination of actinides. Radiochim Acta 97(1) 9-16... 

The alpha activity of uranium in soil samples from Slovakia was determined after a relatively simple sample preparation procedure (Donoval and Matel 2001). The soil samples were dried, ground, and ashed at 550°C, leached with HNO3 + HCl and HNO3 + HF. This was followed by solvent extraction, chromatographic separation of uranium from thorium, deposition with NdFj and alpha spectroscopy for the determination of the 238U/234U ratio. 

Many systems using either HDEHP or Aliquat 336 as the stationary phase have been studied for extraction chromatographic separation of americium tracer. An Aliquat 336 (nitrate-form)-kieselguhr system has been used recently both in the USA and in Europe to separate milligram to gram amounts of americium from curium [70, 71]. 

Ar-O (4 1) atmosphere separation with naphthenic-HCl system Extraction chromatographic separation with bis (2-ethyIhexyl) phosphate on ECieselgulir Li-chromosorb cation exchanger, 2-hydroxy isobutyric acid... 

Spectrography R PrsOii Extraction chromatographic separation with CLP-507 resin 9 ppm D. Wang et al. (1986)... 

Cao, X., Yin, M., and Li, B. (1999). Determination of rare earth impurities in high purity gadolinium oxide by inductively coupled plasma mass spectrometry after 2-ethylhexyl-hydrogen-ethylhexy phosphonate extraction chromatographic separation. Talanta 48(3), 517. 

Used as dipotassium salt for extraction-chromatographic separation of Se(/F) from Se(K7). Cryst. (H2O) (as di-K salt). Sol. H2O (di-K salt). 

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