Abstract: A mass spectrometer includes an inductive coupled plasma source whose flame is near ground potential, an interface, a flight tube, and an analyzer that includes magnetic and electric sectors, and an ion detector, which detector is operated at high voltage for ion acceleration. The magnetic sector includes a magnet and pole pieces that are insulated electrically relative to the flight tube. The pressure within the interface preferably does not exceed 10.sup.-3 mbar. By varying the magnetic field and the acceleration potential, identification of a specified mass over defined time intervals is carried out. The disclosed mass spectrometer provides improved coupling between the plasma ion source and a double-focussing analyzer, while advantageously providing a low voltage regime for the plasma source.

Abstract: Background of the invention is the isotope ratio analysis of carbon and nitrogen as components of hydrocarbon compounds. The separation into individual components takes place in a gas chromatograph and oxydation in a downstream combustion oven, into, inter alia CO.sub.2 and N.sub.2. In general CO.sub.2 is present in a much larger quantity than N.sub.2. The measurement values on the mass spectrometer have accordingly different dimensions. In order to approximate the peak values, a dilution with additional helium as a carrier gas takes place in the analysis of CO.sub.2. This has the additional advantage that the helium as a carrier gas, which is present anyway, as a result is present in approximately equal quantities relative to the CO.sub.2 and N.sub.2 in the ion source of the mass spectrometer. The dilution takes place in the region of a so-called open split (18).