Vg Instruments Group Limited

Elizabeth J Jumeau

Philip A Freedman

Keith Hall

Christiane Pachiaudi

Roger Guilluy

Jean P Riou

The invention provides a method and apparatus for the mass spectrometric determination of the isotopic composition of an element comprised in a sample by gas chromatography-isotopic ratio mass spectrometry. As a sample elutes from the column of the gas chromatograph it enters a sample conversion means which converts the element to an analysis gas (a gas comprising the element in elemental form or in the form of a simple compound, e.g. nitrogen or carbon dioxide) which is admitted into the mass spectrometer only during a second time interval corresponding to the elution of the peak containing the sample from the column. One or more calibration samples of a reference gas are admitted into the spectrometer during first time intervals which do not overlap the second time interval, thereby minimizing the contribution of the analysis gas to the reference gas mass analysis, and vice versa. Various devices are provided to minimize disturbance to the flow of gas into the spectrometer during practice of the method.

Method and apparatus for the determination of isotopic composition

The invention comprises methods and apparatus for the mass spectrometric determination of the isotopic composition of an element comprised in an analysis gas (that is, a gas comprising the element in elemental form or in the form of a simple compound, e.g., nitrogen or carbon dioxide). First and second flows of a carrier gas (e.g., helium) are simultaneously passed into the mass spectrometer, 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 chroatograph through which a sample containing the element is passed, and conversion means to convert the eluting sample into the analysis gas.

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Leftwich, United Kingdom

Elizabeth J Jumeau