Isotope dilution

[2] In the 1930s, US biochemist David Rittenberg pioneered the use of isotope dilution in biochemistry enabling detailed studies of cell metabolism.

[3] Isotope dilution is analogous to the mark and recapture method, commonly used in ecology to estimate population size.

The number of fish native to the lake can be calculated using the following equation: This is a simplified view of isotope dilution but it illustrates the method's salient features.

In a laboratory setting, an unknown (the "lake") may contain a quantity of a compound that is naturally present in major ("blue") and minor ("yellow") isotopic forms.

For example, all National Metrology Institutes rely significantly on isotope dilution when producing certified reference materials.

These ideas combine to give Solving this equation leads to the optimum composition of the blend AB, i.e., the geometric mean between the isotopic compositions of standard (A) and spike (B): This simplified equation was first proposed by De Bievre and Debus numerically[4] and later by Komori et al.[6] and by Riepe and Kaiser analytically.

This preparatory step is called the reverse isotope dilution and it involves a standard of natural isotopic-composition analyte (denoted as A*).

First proposed in the 1940s[10] and further developed in the 1950s,[11] reverse isotope dilution remains an effective means of characterizing a labeled material.

Isotope dilution calibration plots sometimes show nonlinear relationships and in practice polynomial fitting is often performed to empirically describe such curves.

[14] When calibration plots are markedly nonlinear, one can bypass the empirical polynomial fitting and employ the ratio of two linear functions (known as Padé approximant) which is shown to describe the curvature of isotope dilution curves exactly.