Measurement of deuterium in water by the falling drop method

The falling drop method for the isotopic analysis of water sample is fully described. The optimum parameters of the ultra thermostat, the micropipet, the drop size, and the dropping medium for maximum accuracy are discussed. The o-fluorotoluene used should be of the highest purity elsewhere non-reproducible results are obtained. The accuracy obtained is 0.001% up to 0.096 mole% D2O and 0.01% up to 0.994 mole% D2O, although the relative accuracy is the same ±1.4% through the whole calibration curve and is comparable with that of mass spectrometry.