Quantitative comparisons using liquid chromatography with dual-label radioactivity measurements for evaluation of...

Dual-label methods with radiometric measurements with liquid chromatography are evaluated for assessing effects of impurities and isotopic composition in reaction experiments. The procedure is suitably sensitive to detect interferences caused by effects of impurities in reactants, isotope exchange during reaction and effects of kinetic differences due to differing masses of the differently labeled forms. The methods show marked improvements in data quality for comparisons of product formations and relative product abundances in multiple-pathway reaction systems. The results from computer simulations for the procedures are shown to be relatively unaffected by large variations in uncertainties in pretreatment steps and volume measurements. Moreover, these methods yield much better quantitative results than do commonly used corresponding conventional comparisons, and the benefits are corroborated by results from experiments with microsomal reactions.