Measurement of D2O concentrations at tracer levels in small samples obtained from paediatric patients

A micro-method is described for the determination of trace amounts of D2O in serum, saliva and urine, requiring 100 microliters of sample. H2O/D2O are rapidly isolated from serum, saliva or urine by vacuum distillation. D2O concentrations in H2O are detected by infrared spectroscopy utilizing the integrated absorption of the OD-bond at 2510 cm-1 in the range of 2675 to 2460 cm-1. Calibration is done using standard solutions of H2O/D2O. The separation of D2O/H2O is necessary because of the varying background absorption of the sample. The recovery of D2O after distillation is 100%. The absolute error is 25 mg/kg (+/- 2 s) of D2O leading to a precision of 17.5% at 150, 2.8% at 1000, 1.3% at 2000, 0.9% at 3000, 0.7% at 4000 and 0.5% at 5000 mg/kg of D2O. The usefulness of the method is evaluated by 9 determinations of total body water and water turnover in 7 healthy subjects drinking a mixture of H2O/D2O. Total body water related to body surface is 23.3 +/- 0.9 l/m2 in males and 20.5 +/- 1.5 l/m2 in females. Water turnover is determined by analysing the decrease of D2O concentrations in blood between 6 and 31 days. A mean of 1.53 +/- 0.13 l/m2.d in males in 1.48 +/- 0.17 l/m2.d in females was found.