Analytical aspects of measuring H-2/H-1 and O-18/O-16 ratios in urine from doubly labelled water studies by high-temperature conversion elemental analyser-isotope-ratio mass spectrometry

摘要

RATIONALE: Total Body Water (TBW) and Total Energy Expenditure (TEE) are routinely measured in free-living conditions by the (H2O)-H-2-O-18 method. Isotope eliminations can be measured from spot urine samples by HTC-EA IRMS, but only after cumbersome cryogenic distillation to extract water. Distillation may, however, be replaced by charcoal treatment and filtration. This study tested (1) the effect of sample treatments (filtration versus distillation) on the isotope ratios, (2) the effect of different ways of normalization that respect or not the principle of identical treatment of the sample and references, and (3) the impact on the biological outcomes.