Infrared-spectrometric determination of D2O in biological fluids. Reappraisal of the method and application to the measurement of total body water and daily water turnover in the dog.

The determination of D2) in biological fluids by means of infrared spectrometry was reinvestigated. When the temperature of a solution, containing D2O in the range from natural abundance to 5 ml . 1-1 increases, its absorbance decreases and the wavenumber of maximum absorption shifts to a higher value. Both changes are linearly related to the change in temperature. Storage for 17 d in either glass or polyethylene tubes does not affect the D2O concentration. Purification of biological fluids by vacuum-sublimation removes all substances which also absorb at the O-D vibration band and the recovery of D2O from plasma and urine is complete. The partition ratio of D2O between plasma water and red cell water equals unity, and the same holds for plasma water and urine water over a wide range of urine flows and osmolalities. The arterial and urinary disappearance curves of D2O, measured over several days, both permit the calculation of the total amount of body water (Vbw), the daily water turn-over (F) and the half-time of water in the body (t1