Abstract: The invention comprises a novel sample introduction system which incorporates a venturi pump to convey a sample gas to an analytical instrument at atmospheric pressure. An APCI, ICP or MIP mass spectrometer is preferred as the analytical instrument. Using such an inlet with an APCI mass spectrometer, the real-time analysis of trace materials present in breath is facilitated, enabling, for example, the release of compounds responsible for aroma and taste to be analysed during eating and drinking. The invention can also be used for headspace analysis and for monitoring the release of fragrances from skin or clothing.