D and 18O analysis of milligram water samples

Possibilities and limits of the routine preparation lines and procedures for D and 18O isotope analyses of water samples are thoroughly discussed for the specific case when the mass of the sample is limited to single milligrams. It is demonstrated that the classical CO2-equilibration technique also provides reliable results for masses of water as low as 10 mg. It appears that error in δ18O for low-mass water samples is influenced mainly by actual accuracy to which this mass is determined. For equilibration of CO2 with low-mass water samples an interesting relationship was observed: the equilibration time increased continuously with decreasing mass of water. Some suggestions are put forward in order to explain this intriguing effect. (author)