Reverse isotope dilution analysis

A plant was grown in an atmosphere containing C Os (3 x 10 CPM//i,mole). After several weeks a leaf extract was prepared for glucose-l-phosphate determination via reverse isotope dilution analysis. To 20 ml of the extract, 1.5 mmoles of unlabeled dipotassium glucose-1-phosphate were added. A small amount of dipotassium glucose-1-phosphate was reisolated from the extract and recrystallized to constant specific activity from aqueous ethanol. The recrystallized salt had a specific activity of 2.6 X 10 CPM//jLmole. Calculate the concentration of labeled glucose-1-phosphate in the extract. 

The preceding method is known as reversed isotope dilution analysis when the compound to be measured is already radioactive. The principle remains the same the activity of the subject compound (measured from a fraction), is carried out before and after dilution with the same compound, non-labelled. The calculations are identical. This analysis is used for the determination of the isotopic carrier in a solution of a radionuclide using one of its stable isotopes. 

As defined by reverse isotope dilution analysis and metabolic profiling experiments, unchanged semduramicin sodium was the major component of total residues in liver at the 6 hour withdrawal period. At later withdrawal times, unchanged semduramicin sodium levels declined by a biphasic pattern in liver similar to that of total residues. 

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

For most applications in the use of tracers the most important factor in regard to purity of the labeled compounds is radiochemical purity. However, it is almost as important that the chemical purity or identity of the labeled compound be clearly established. Most classical methods for determination of chemical purity (melting point, UV, NMR, etc.) are usually inadequate for determination of radiochemical purity. The two basic techniques widely used to determine radiopurity are radiochromatography and reverse isotope dilution analysis. 

In this case, the spike added first is used as a tracer, for example, in metabolic studies, and the second for quantification of the elemental species. Meija et al. [99] investigated the redox interconversion reaction between Cr(III) and Cr(VI) in yeast using °Cr-emiched Cr(III) and Cr-enriched Cr(VI) by least-squares ion intensity-based IPD. They found that the results were in exact agreement with conventional isotope dilution calculations. An example in which IPD was applied for metabolism studies is the determination of the metabolism of butyltin compounds in rats [100]. Sn-labeled MET, Sn-labeled DBT, and Sn-labeled TBT dissolved in tap water were administered orally to the animals. Degradation of the butyltin compounds was studied in different organs by least-squares IPD and their concentrations were determined via reverse isotope dilution analysis using the corresponding compounds of natural isotopic composition as spikes. 

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

Y. KOBAYASHI AND D. V. MAUDSLBY REVERSE ISOTOPE DILUTION ANALYSIS... 

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... 

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