Abstract: The invention relates to a device and method for partial conversion of a fluid sample comprising a plurality of components and a process for on-line determination and analysis of components of a fluid sample comprising a plurality of components. The invention also relates to the use of the device as a sample treatment device.

Abstract: For identifying the concentration of individual types of molecules in a gas mixture, the gas mixture to be investigated is subjected to a selective pre-treatment and the product of this pre-treatment is then mass-spectrometrically investigated. For separate concentration identification of molecules having identical molecular mass, the gas mixture is ionized with primary ions that have an internal energy slightly above that required for generating product ions representing the respective type of molecule of interest and that have a pulse energy of such an amount that the kinetic effect on the ionization is negligible in comparison to the influence of the internal energy. The mass-spectrometric investigation then supplies the sought concentration of the individual type of molecule in a simple and precise fashion.