Robust determination of deuterium abundance in water

Quantitative Deuterium Metabolic Imaging, or DMI, is typically based on the natural abundance deuterium ( 2 H) signal from water that is inherently present in all DMI data. The 2 H level in water depends on many geographical and atmospheric factors, whereby the in vivo 2 H level can be further modified through the administration and breakdown of deuterated substrates. For water to act as an internal concentration reference, the 2 H enrichment needs to be determined on a regional or even per-subject basis. An NMR method is presented to quantitatively and robustly determine the 2 H enrichment in water using dimethyl sulfoxide (DMSO) as an 1 H/ 2 H internal reference. The method, employing a 1 H/ 2 H ratio of water/DMSO ratios, is independent of the amount of water or reference. The method is readily implemented on any modern NMR spectrometer with signal acquisition based on simple, fully-relaxed pulse-acquire methods and standard NMR tubes. The double ratio method is validated on samples with known 2 H enrichments and variations in 2 H water content are demonstrated for bottled spring waters from across the United States, and for human blood plasma during infusions of deuterated glucose and acetate. The presented double ratio method is a robust and practical tool to determine 2 H water enrichment on individual subjects and/or specific geographic regions.