Method and apparatus for the determination of isotopic composition.

摘要

The invention comprises methods and apparatus for the mass spectrometric determination of the isotopic composition of an element comprises in an analysis gas (that is, a gas comprising the element in elemental form or in the form of a simple compound, eg, nitrogen or carbon dioxide). First and second flows of a carrier gas (eg, helium) are simultaneously passed into the mass spectrometer 9, and samples of analysis gas and a reference gas are respectively introduced into the first and second flows during selected time intervals. The time intervals are selected so that mass spectrometric measurements are made on the analysis gas samples in the absence of any signal from the reference gas samples, and v.v. A preferred embodiment comprises a gas chromatograph 28, 29 through which a sample containing the element is passed, and conversion means 30 to convert the eluting sample into the analysis gas.