Development and application of a portable volatile organic compound analyser

Abstract

The subject of this PhD is the development and testing of a portable membrane inlet mass spectrometer (MIMS), for the in-situ measurement of volatile organic compounds (VOCs) in air. There are several types of VOC monitor available, but few are able to monitor in-situ with near real-time measurements at concentrations around or lower than ppm levels. This PhD focuses on the development of the MS-200 and demonstrates its performance in laboratory and field conditions to analysis a range of VOCs. The first chapters of this thesis describe the design considerations that led to the development of the MS-200. It also discusses the working principles of the instrument and the laboratory based performance tests that compare the performance of the MS-200 with the industry standard VOC monitor. As the MS-200 has sensitivity and detection limits down to ppb levels, it overcame the limitations of many other instruments, and enabled its use for many new applications. For example, aromatic and chlorinated hydrocarbons report detection limits of between 600ppt to 20ppb, other VOCs investigated, reported detection limits between 20 to 300ppb, low molecular weight alcohols report detection limits of 0.4 to 6ppm. However, some applications require even lower detection limits, so an alternative inlet system was developed to increase the sensitivity but at the expense of the near real-time measurement capability. Typically the alternative inlet system reduces detection limits by two orders of magnitudes compared with the standard MS-200. Subsequent sections of this thesis describe and discuss a range of real world applications for the MS-200. Most of these investigations were successful, although a number would need some further work before the MS-200 would be capable to perform such applications routinely in a commercial environment. The applications discussed include: Investigations into arson where the instrument can be used to detect remnants of accelerants used without needing to return samples to the lab, giving the potential to save both time and money; Monitoring personal exposure to benzene when refuelling a petrol car, where the MS-200 demonstrated the advantage of portable real-time monitoring. It was found that during refuelling the operator could be exposed to benzene concentrations of a few hundred ppb to 4ppm for a duration of about 3 minutes; Measuring VOC markers in human breath as a diagnostic tool for cancer and other illnesses; The use of the MS-200 as an "artificial nose" in the food quality and flavour analysis. The thesis discusses the advantages and limitations of this technology as well as providing a series of recommendations for its future development.