Hydrogen Stable Isotopes
| Stable isotopes | Terrestrial abundance (%) | Common standards |
| 1H and 2H | 99.985 and 0.015 | SMOW (Standard Mean Oceanic Water, IAEA, Vienna) |
The heavier of the two isotopes of hydrogen is commonly called deuterium, so it can be represented by D as well as 2H. The ratio of 2H to 1H in a sample is usually measured relative to that in a standard, and expressed in parts-per-thousand (per mil):
δ2H (‰) = [{(2H/1H sample)/(2H/1H standard)} -1] x 1000
The hydrogen in bulk samples or compounds is oxidised to water during combustion, but the isotopic composition of water is not measured directly and it presents various problems. For example, it can condense onto various surfaces in the mass spectrometer, which results in dramatic isotopic fractionation. Consequently, the water is reduced to hydrogen by passing it over hot zinc or through a uranium reduction furnace at low pressure (<2.0 x 10-5 torr) in order to prevent contamination. The hydrogen is then passed into the isotope-ratio mass spectrometer.
For further information see 'Isotope interpretation'.
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