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Gas Chromatography–Mass Spectrometry Assay of the 18O Enrichment of Water as Trimethyl Phosphate

✍ Scribed by Daniel Z. Brunengraber; Brendan J. McCabe; Jill Katanik; Stephen F. Previs

Book ID
102564001
Publisher
Elsevier Science
Year
2002
Tongue
English
Weight
75 KB
Volume
306
Category
Article
ISSN
0003-2697

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✦ Synopsis

We have developed an assay for determining the 18O enrichment of water in biological fluids. Urine, plasma, or whole blood is reacted with phosphorous pentachloride to yield phosphoric acid. Derivatization of phosphoric acid with diazomethane generates trimethyl phosphate. The enrichment of trimethyl phosphate is nearly four times that of water and is assayed using gas chromatography-mass spectrometry (electron impact ionization). Yang et al. (1998, Anal. Biochem. 258, 315-321) assayed the 2H enrichment of body water after exchange with acetone, by gas chromatography-mass spectrometry. The combination of our 18O method and the 2H method of Yang et al. allows one to measure energy expenditure via "doubly labeled" water (2H(2)O + H(2)18O), using small samples of body fluids. These techniques were used to measure energy expenditure in mice, in which the 18O enrichment of body water can be monitored down to 0.025%.

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