Water enriched in the rare stable isotopes: Preparation, measurement and applications

The subject of this thesis is water with increased abundances of the rare stable isotopes 2H and 18O (and to some extent also 17O). Such artificially enriched (or "labelled") waters are often used in biomedicine, for establishing the total amount of body water (and thus body composition) of humans and animals and also for measuring their energy expenditure. These non-evasive totally harmless techniques offer great advantages, however they require accurate and precise "isotope ratio" measurements as well as reliable reference waters for calibration. In the thesis a prototype optical (so-called OF-CEAS) instrument for more sensitive and precise measurements of the three isotope ratios in isotope-labelled water is described. Furthermore, the production and certification of two sets of labelled reference waters is documented. These sets of waters are now established as international reference materials for biomedical research and as such distributed by the International Atomic Energy Agency (IAEA).
Another, very different use of these isotope-labelled waters lies in the realm of thermometry. The SI unit of temperature, the Kelvin, is defined using the temperature of the so-called triple point of water (in which all three phases, solid, liquid and vapour, coexist). The triple point temperature, however, depends on the isotopic composition of the water used. We performed an exact quantification of isotope effects on this triple point temperature by measuring this temperature for a series of differently, and well-known isotope-labelled waters. We performed these measurements in collaboration with the National Dutch Measurement Institute VSL. Our work has lead to both a general higher quality of temperature measurement, and to a more accurate realization of the Kelvin according to the SI definition.