Inverse isotope dilution analysis

The above equation is the basic equation of inverse isotope dilution analysis and indicates that the unknown amount q of active material A can be deduced by adding r... 

The second general category of radiochemical analysis involves adding a radioactive substance to the sample, manipulating the sample by chemical or physical means, measuring the radioactivity, and ultimately calculating the amount of the component of interest. This category includes direct and inverse isotope dilution analysis, radiochemical titrations, and radiorelease methods of analysis. 

In DIDA, a radioactive form of the component of interest is added to the sample and the quantity of the inactive form initially present is determined. In some instances, one may wish to determine the amount of a radioactive substance in the sample. A method similar in principle to DIDA can then be used wherein a quantity of an inactive form of the component of interest is added to the sample, the sample is purified without regard to quantitative recovery, and the amount of the recovered component and its activity are measured. From this information, the quantity of the radioactive substance initially present in the sample is calculated. This method is referred to as inverse isotope dilution analysis (IIDA). 

Radiometric analysis, or radiometry, is a method of analysis in which a radioactive tracer is employed as an indicator or a reagent. Among them, the most important one is the isotope dilution analysis discussed separately below. Isotope dilution analysis is also used to determine the amount of radioactive elements or compounds (inverse isotope dilution analysis). 

Inverse isotope dilution analysis. This variation is a method to determine not an inactive compound hut a radioactive one. To he determined is the mass X of a certain radioactive compound (or ion), whose specific activity is known to be So, in a sample. To the sample solution is added a solution containing W of the same but inactive compound (spike). If the specific activity of the compound after this addition and thorough blending is taken to be S, then... 

The weak point of the above inverse isotope dilution analysis is that the specific activity So of the compound to be determined in the original sample solution must be known. This can be avoided by double isotope dilution analysis. In this type of analysis, two portions of exactly the same amount are taken from the sample solution. The mass of the radioactive compound in each portion is taken to be X. To the portions are added different masses Wi and W2 of the inactive compound. Taking the specific activities of the compound in the portions after this to be Si and S2,... 

Hasegawa, H. Matsukawa, T. Shinohara, Y. Hashimoto, T. Assessment of the metabohc chiral inversion of D-leucine in rat by gas chromatography-mass spectrometry combined with a stable isotope dilution analysis. Drug Metab. Disp. 2000, 28, 920-924. 

Spectra of the Co(III) complexes of [a- 0, 0]dADP that demonstrate the validity of this configurational analysis are shown in Fig. 11 the diastereomers of labeled dADP were prepared enzymatically from the diastereomers of cyclic [ 0, 0]dAMP, as described in Section IV,A, and diluted with an equal amount of unlabeled dADP prior to complex formation. In each spectrum the 0 perturbations measured on the epimeric complexes yield complementary configurational information, and a reversal of the magnitudes of the isotope-induced chemical shift by inversion of the configuration of the chiral a-phosphoryl groups is apparent when the spectra are compared. This technique was subsequently used by both Frey (Sammons and Frey, 1982) and Eckstein (Connolly et al, 1982) to determine the configurations of samples of [a- 0, 0]ADP synthesized chemically from ADPaS. 

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