Abstract: An apparatus to directly take a sample of expired air from a subject which utilizes a stopper (3) with two distinct position. When the stopper (3) is in the upper position, it allows air blown in via the cannula (6) to scavenge the interior space of the tube (1) until the control (11,12, or 13) has indicated a sufficient volume. The cannula (6) is then pulled by the operator so that a blind stop (7) obturates the opening of an evacuation pipe (10) connected to the control. The stopper is then moved to a lower position to seal the sample of air in the tube (1).

Abstract: 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.

Abstract: 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.