Abstract
The measurement of small quantities of gases and volatiles in air is used nowadays in many different fields of science, such as chemistry, physics, biology, food science and medicine. The study of these minute quantities of gases requires highly sensitive detectors. Using such detectors to monitor the emission of molecules can provide useful insight into processes inside the emitter. However, the sources, amounts and types of volatile organic compounds can vary greatly, requiring different types of dedicated or highly versatile detectors. This thesis is about the development and application of trace gas detectors based on mass spectrometers. To be more specific, products of chemical reactions of trace gas molecules with H3O+ ions are studied. This experimental technique is called Proton-Transfer Reaction Mass Spectrometry (PTR-MS). The nature of the proton-transfer reaction enables the detection of extremely low levels (i.e. at (sub-) ppbv level; 1:1.000.000.000) of many different types of trace gases at a high time resolution. This thesis includes a description of the thermodynamics and chemistry behind the PTR-MS technique and contains a large variety of studies in different areas of application. These examples include the study of biological processes in plants and fruits and the quest for biomarkers of diseases in human breath. Besides the application of the PTR-MS technique, this thesis also contains a description of the development of a new type of PTR-MS detector, equipped with an ion trap mass spectrometer instead of the conventional quadrupole mass filter. This new system is shown to provide highly improved possibility of identification of detected volatile organic compounds.
