Development and Verification of Injection Systems for Proton Transfer Reaction Mass Spectrometry (PTR-MS) Analysis of Diverse Volatile Organic Compounds
thesisposted on 04.02.2015, 16:40 by Milan Ashvinbhai Patel
The PTR-MS is the well-established technique in the field of analysis of volatile compounds from air, food and breath. The principal advantage of the technique is real time analysis, high sensitivity and less fragmentation. However, this technique requires the samples in the gas phase and therefore, liquid samples cannot be analysed directly. The leading focus of this thesis was to develop a technique that will enable the use of the aqueous sample to extend the application of the PTR-MS. This thesis documents the design and calibration of the sample inlet systems and subsequent application development. The initial work dedicated to develop and calibrate the heated inlet system (HIS) to inject the aqueous sample, volatile organic solvent sample and headspace above the liquid sample. The subsequent development and calibration of the capillary inlet system (CIS) for the continuous injection of the aqueous sample is documented in this thesis. Applications for the environmental, food and diagnostic field were developed. In the environmental field, identification and calibration of the pesticide compounds from the water was performed. Acceptable sensitivity and limit of quantification (~ 1.0 μg/mL) was achieved for organophosphate pesticides used in the experiments. Further work is required to improve the sensitivity and lower the limit of quantification to ng/mL levels instead of μg/mL levels. Additional work is required for the detection and quantification for the chlorinated pesticides, as PTR-ToF-MS instrument used in this thesis is not able to detect these pesticides. For the food field, Scotch whiskies were successfully characterised based on their VOC profiles. Lastly, for the diagnostic field, urine headspace from five volunteers was analysed, to identify and to quantify different VOCs. Different VOCs (different ketones and aldehydes) were successfully identified and quantified. The precision of the measurement for acetone and acetaldehyde was 13.7% and 15.6%, respectively. Further work with bigger pool of volunteers, and a technique in which urine samples can be injected directly is required to establish the database for the VOCs and to improve the sensitivity of VOCs. Lastly, a two-stage technique was developed to identify isobaric compounds that are chemically different but have a similar mass. For example, butanal which is an aldehyde and butanone, which is a ketone, are chemically different but both compounds have a mass of 72 amu. In this thesis, as stated above, it is documented that liquid samples can be analysed by using PTR-MS, but further work is required to resolve the issues like contamination and handling of large sample volume.