Fourier transform infrared spectroscopy measures 1H/2H ratios of native water with a precision comparable to that of isotope ratio mass spectrometry.

A fast and easy method is described which uses Fourier transform infrared spectroscopy (FT-IR) to measure the 1H/2H ratio of aqueous samples of less than 100 microliters with high precision (+/- 0.2-0.5% in the range of 89 to 2680 microliters/l). Using a thermostat-controlled CaF2 cell, low resolution absorption specta (8 cm-1) are measured. The integral of absorption in the range of 2600 and 2460 cm-1 (O2H vibration) is used to analyse the 2H content of the sample. For measurements at low enrichment five standards are used (SLAP: 89.00 microliters/l, GISP: 126.3 microliters/l, V-SMOW: 156.0 microliters/l, all from the International Atomic Energy Agency, Vienna, Austria, standard 1: 183.3 microliters/l, standard 2: 222.5 microliters/l, both prepared by weighing and controlled by isotope ratio mass spectrometry (IR-MS)). For measurements at high enrichment three standards are used (standard 2: 222.5 microliters/l, standard 3: 1323 microliters/l, standard 4: 2680 microliters/l, all prepared by weighing and controlled by IR-MS). Measured and reported 2H concentrations coincide very well, two samples for quality control (145 and 1612 microliters/l) were measured with a precision of 0.3 and 0.4% corresponding to +/- 0.5 and 5.9 microliters/l.