Hydrogen Stable Isotopes

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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