Abstract: The invention relates to high performance ion traps used as mass spectrometers which in spite of a variable thermal load require a high constancy of the mass scale calibrated in. Ion traps consist at least of one ring electrode, two end cap electrodes, and suitable fixing elements which determine the distance between the electrodes. When exposed to a thermal load, the parts of the ion trap are subject to thermal expansion, which leads to a change in field intensities even if the applied RF voltage is constant, and thus to an apparant shift of masses. The invention consists of selecting the thermal expansion of the ion trap parts in such a way that when a constant RF voltage is applied, the field intensity within the trap remains constant by first approximation, in spite of the altering geometric form and expansion with changing operating temperature. In this way, displacement of the mass scale is avoided. To compensate an unavoidable thermal expansion .DELTA.r.sub.

Abstract: The invention concerns a sampling device for a mobile analysis unit, in particular a mass spectrometer (13), used for the purpose of monitoring chemical substances on ground surfaces. It possesses at least one sampling wheel which revolves around an axle and which consists of a silicone tire (5) for picking up molecules of substances to be monitored and a wheel rim (6) upon which the silicone tire is fitted. The wheel rim (6) is made of metal such as stainless steel or aluminum. This means that on the one hand contamination of the silicone tire (5) by vapors from the wheel rims (6), in the course of long-term storage of the sampling wheels in airtight, closed storage containers, is prevented. On the other hand, the invention facilitates an advantageous construction of the wheel rim (6), involving the mounting of two, thin-walled rim halves (9) with rivet holes.

Abstract: An ultra-high vacuum valve for the admission of substance mixtures into an analytical measuring instrument limits the flow path of the substances to as small a flow chamber as possible with controllable chamber wall adsorption properties. The elastic wall sections necessary for movement of the valve piston are located in a mechanical chamber separated from the flow chamber by a wall. The mechanical chamber is evacuated by means of a separate vacuum duct and a seal is used to seal the valve piston where it passes through the wall.