Derivative isotope dilution analysis

Reverse Isotope Dilution Analysis. 137 Derivative Isotope Dilution Analysis 137 Substoichiometric Isotope Dilution... 

Isotope dilution analysis is applied to the following analysis. Calculate the amount of the compound Y present in the sample and express your answer as percent by weight. A 1-g sample is analyzed for compound Y, molecular weight of 150. A derivative is formed of compound Y and the added radioactive Y (1.5 mCi at a specific activity of 3 mCi/mmol). The derivative, molecular weight of 150 (1 mol of compound Y per mole of derivative), is recrystallized until pure. It has a specific activity of 4.44 x 103 dpm/mg. 

Comparative aroma dilution analyses of the headspace of aqueous solutions, containing either the total volatiles isolated from a fresh coffee brew or these volatiles mixed with the melanoidins isolated from coffee brew, revealed drastic losses of odorous thiols, 2-furfurylthiol, 3-methyl-2-butenethiol, 3-mercapto-3-methylbutyl formate, 2-methyl-3-furanthiol, and methanethiol, in the presence of melanoidins.509 The first compound was affected most, the reduction being 16-fold, and was accompanied by an overall reduction in roasty-sulfury aroma. The rapid loss of thiols was confirmed by stable-isotope dilution analysis. [2H]-NMR and LC-MS gave strong evidence that the thiols become covalently bound via Maillard-derived pyrazinium compounds. 

Isotope dilution analysis (IDA) involves mixing an aliquant of the sample with an aliquant of an artificially enriched isotope of the element to be analyzed. The content of the latter in the original sample is derived from the results of the isotopic analysis of the mixture compared to the isotopic compositions of the sample and of the enriched isotope. The term spiking is often used to refer to the mixing step. The aliquant of enriched isotope added to the sample is also commonly called a spike. IDA is used in particular for the determination of uranium, plutonium, or thorium in solutions of irradiated nuclear fuels. It has also been used for an independent measurement of the total volume or mass of solution in accountability tanks of chemical processing plants. 

QUANTITATIVE TECHNIQUES Isotope dilution analysis Direct dilution analysis Reverse isotope dilution analysis Derivative analysis Double isotope dilution analysis Saturation analysis Radioenzymatic assays... 

This procedure is an elegant combination of derivative analysis and reverse isotope dilution analysis. It can be carried out in either of two ways. Firstly, a trace of the compound to be measured is added in labelled form to the mixture to serve as an indicator. The compound is then converted to a suitable derivative with the aid of a labelled reagent the indicator and reagent must be labelled with two different isotopes. After reaction, which does not have to proceed quantitatively, an unlabelled carrier is added and the... 

Figure 7.7 Derived molar flow electropherograms of metaUothionein preparation from isotope dilution analysis on an anionic polymer-coated column, prepared by immobilising poly (2-acrylamido-2-methyl-1-propanesulfonic acid) on the fused-silica surface via a linking agent. (Reprinted with permission. Copyright (1991), American Chemical Society.)...

ABA is detected and quantified by enzyme immunoassay with a monoclonal antibody.578 The detection limit of immunoassay with a monoclonal antibody is about 0.02 pmol however, enzyme immunoassay cannot exclude cross-reactivity with unknown substances, so GC- or LC-SIM analysis using the stable isotope dilution method is recommended for correct quantitation. As internal standards labeled with the stable isotope, deuterated derivatives of ABA such as [3, 5, 5, 7, 7, 7 -2H6]ABA (ABA-//6)579 and [7, 7, 7 -2H3] derivatives of phaseic and dihydrophaseic acids580 are used. 

In clinical chemistry the determination of stable elements by radiochemical methods offers no outstanding advantages over alternative methods, but the use of radioisotopes for determining organic compounds is developing rapidly. In isotope dilution methods (G6), a pure but radioactive form of the compound to be measured is mixed with the sample, a fraction is isolated, and its activity is determined. In radio-metric or derivative analysis (W14), a radioactive reagent is allowed to react with the analyte the labeled compound is separated and its activity is measured. The isotopes commonly used are C,... 

TBDMS derivatives have been applied to the analysis of organic acids in urine as oxime-TBDMS [91] and in tissues [92] as methoxime-TBDMS derivatives. The intense [M —57]" ions found in the spectra of the latter were shown to contain all the original hydrogen atoms. Thus, the derivatization should find application in quantification by isotope dilution and in metabolic studies with deuterium-labelled compounds. TMS and oxime-TMS derivatives, however, still remain the more popular derivatives for general screening, a consequence of the more structurally informative mass spectra, shorter analysis times and the ready availability of reference spectra. 

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