Measurement of Small Isotope Effects

Mass spectrometric analysis of isotope ratios is in principle very accurate (isotope ratio mass spectrometers were developed for geochemical investigations), but the analytical problem comes from possible fractionation of isotopes in the workup procedure. Traditionally, isotope ratio mass spectrometry measurements of kinetic isotope effects have been confined to reactions which give a small molecule product (such as CO2), which can be directly introduced to the mass spectrometer. 

It is possible to count the ratio of the disintegrations of two p-emitters of different energies, such as and H, with very high precision. This fact can be 

Fits to such an expression with all parameters as variables are very ill-conditioned and it is advisable to measure in a separate experiment, constrain k to within 10% of its separately measured value, ensure that B —A and only analyse time courses which are obviously, by visual inspection, not simple exponentials (preferably they should have definite maxima and minima). 

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