Interferences chemical separations

Other types of reactions can be used to chemically separate an analyte and interferent, including precipitation, electrodeposition, and ion exchange. Two important examples of the application of precipitation are the... 

When the analytical method s selectivity is insufficient, it may be necessary to separate the analyte from potential interferents. Such separations can take advantage of physical properties, such as size, mass or density, or chemical properties. Important examples of chemical separations include masking, distillation, and extractions. 

Other reasons for investigating plutonium photochemistry in the mid-seventies included the widely known uranyl photochemistry and the similarities of the actinyl species, the exciting possibilities of isotope separation or enrichment, the potential for chemical separation or interference in separation processes for nuclear fuel reprocessing, the possible photoredox effects on plutonium in the environment, and the desire to expand the fundamental knowledge of plutonium chemistry. 

Analyte dilution sacrifices sensitivity. Matrix matching can only be applied for simple matrices, but is clearly not applicable for complex matrices of varying composition. Accurate correction for matrix effect is possible only if the IS is chosen with a mass number as close as possible to that of the analyte elements). Standard addition of a known amount of the element(s) of interest is a safe method for samples of unknown composition and thus unknown matrix effect. Chemical separations avoid spectral interference and allow preconcentration of the analyte elements. Sampling and sample preparation have recently been reviewed [4]. 

Chemical separation techniques can be used to reduce spectral interferences and concentrate the analyte. These techniques include solvent extraction(39) and hydride generation(39, 46, 47). At Imperial College, the hydride generation technique is being used on a daily basis(46) for the analysis of soils, sediments, waters, herbage, and animal tissue. The solvent extraction technique is ideally suited for automated systems where the increased manipulation is carried out automatically, and a labor intensive step and sources of contamination are avoided. 

Chemical separation of matrix and preconcentration of analytes is used to avoid matrix effects, clogging effects on the cones and disturbing interferences of analyte ions with polyatomic ions of matrix elements and plasma gases. A trace/matrix separation method is required for ultratrace analysis. 

Conventional radiochemical methods for the determination of long-lived radionuclides at low concentration levels require a careful chemical separation of the analyte, e.g., by liquid-liquid, solid phase extraction or ion chromatography. The chemical separation of the interferents from the long-lived radionuclide at the ultratrace level and its enrichment in order to achieve low detection limits is often very time consuming. Inorganic mass spectrometry is especially advantageous in comparison to radioanalytical techniques for the characterization of radionuclides with long half-lives (> 104 a) at the ultratrace level and very low radioactive environmental or waste samples. 

A major topic in isotope mass spectrometry is the determination of the half-lives of long-lived radionuclides. De Bievre and Verbruggen34 determined the half-life of 241 Pu for 3-decay in the isobaric radionuclide 241 Am on material from Oak Ridge that had initially been about 93% isotopically enriched. Due to the isobaric interference of 241 Pu and 241 Am radionuclides during mass spectrometric measurements by TIMS, Am had to be removed by chemical separation immediately (less than 48 h) prior to measurements as described in reference 34. On the basis of all the measurements performed over an extended period of more than 20 years and after considering the possible effects of systematic errors during these measurements, a half-life for the 3 decay of 241 Pu of (ti/2 = 14.290 0.006 a) was reported.34... 

Chemical Separation Steps. The radioanalytical or radiochemical procedure is a series of chemical steps performed on the sample to insure that the suitably exchanged radioanalyte plus carrier are separated from substances, both radioactive and non-radioactive, that will interfere with the analysis. The final sample must be free of radionuclides that could be mistaken as the radioanalyte when counted. It also must be free of non-radioactive elements that would falsely elevate the chemical yield (recovery), excessively attenuate the emitted radiation, or otherwise interfere in the identification and quantification of the radioanalyte. 

Many aerosol materials have been used, and the aerosol material can be specifically chosen to minimize interference with the chemical separation being conducted. Widely used were KC1 aerosols which can easily be generated by sublimation of KC1 from a porcelain boat within a tube furnace. By choosing a temperature between 650°C and 670°C, specially tailored aerosols with a mean mobility diameter of about 100 nm and number concentrations of few times 106 particles/cm3 could be generated. The same technique could be applied to produce MoOj aerosols. Carbon aerosol particles of similar dimensions were generated by spark discharge between two carbon electrodes. 

With modem instrumentation it is often possible to make determinations of individual elements without the necessity for any chemical separations, but while mutual interferences for AAS and ICP emission spectrometry are often small the sensitivity, for example, for iridium, may be unacceptably low and chemical separations are required. The separation of rhodium from iridium is one of the most challenging analytical tasks. Ruthenium and osmium are most commonly separated from other PGMs and matrix elements by distillation of their tefroxides. ... 

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