Use of an automated chromium reduction system for hydrogen isotope ratio analysis of physiological fluids applied to doubly labeled water analysis

The doubly labeled mater method is commonly used to measure total energy ex penditure in free-living subjects. The method, however, requires accurate a nd precise: deuterium abundance determinations, which can be laborious. The aim of this study was to evaluate a fully automated, high-throughput, chro mium reduction technique for the measurement of deuterium abundances in phy siological fluids, The chromium technique aas compared with an off-line zin c bomb reduction technique and also subjected to test-retest analysis. Anal ysis of international mater standards demonstrated that the chromium techni que was accurate and had a within-day precision of <1%. Addition of organic matter to water samples demonstrated that the technique was sensitive to i nterference at levels between 2 and 5 g l(-1). Physiological samples could be analyzed without this interference, plasma by 10 000 Da exclusion filtra tion, saliva by sedimentation and urine by decolorizing with carbon black, Chromium reduction of urine specimens from doubly labeled water studies ind icated no bias relative to zinc reduction with a mean difference in calcula ted energy expenditure of -0.2 +/- 3.9%. Blinded reanalysis of urine specim ens from a second doubly labeled mater study demonstrated a test-retest coe fficient of variation of 4%. The chromium reduction method was found to be a rapid, accurate and precise method for the analysis of urine specimens fr om doubly labeled mater, Copyright (C) 2000 John Wiley & Sons, Ltd.