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GC-MS) Techniques and Selected Ion Flow Tube Mass Spectrometry (SIFT-MS) Assessment of Volatiles Produced from Nitric Oxide Producing Smart Dressings

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The detection of trace volatiles from complex matrices using gas chromatography mass spectrometry (GC-MS) techniques and selected ion flow tube mass spectrometry (SIFT-MS) assessment of volatiles produced from nitric oxide producing smart dressings Oliver John Gould A thesis submitted in partial fulfilment of the requirements of the University of the West of England, Bristol for the degree of Doctor of Philosophy Faculty of Health and Applied Sciences, University of the West of England, Bristol 2019 Copyright declaration This copy has been supplied on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgment. i Acknowledgements I would like to thank my supervisors Professor Norman Ratcliffe, and Associate Professor Ben de Lacy Costello for all their help, guidance, and support over the course of this work, and for their co-authorship on the published versions of chapters 2 and 3. I would also like to thank Dr Hugh Munro and Edixomed Ltd for financial support and scientific guidance with chapter 4. I would like to thank my co-authors on the publication of chapter 2 Tom Wieczorek, Professor Raj Persad. Also thank you to my co-authors on the publication of chapter 3, Amy Smart, Dr Angus Macmaster, and Dr Karen Ransley; and express my appreciation to Givaudan for funding the work undertaken in chapter 3. Thank you also to my colleagues and fellow post graduate research students at the University of the West of England for always being on hand for discussion and generation of ideas. A special mention to Dr Peter Jones who has been mentoring me on mass spectrometry for a number of years. On a personal note I would like to give a very special thank you to my mother Maya Gould who has been a constant source of direction and strength over the years. I would also like to give special thanks to Caroline for her continuing love, support, and patience. ii Abstract Volatile compounds (VCs) hold the potential to diagnose and monitor disease states in a cost effective, rapid, and most importantly non-invasive manner. Gas chromatography mass spectrometry (GC-MS) has been in use since the 1960s and remains the gold standard for qualitative VC analysis. Within this thesis three novel methods and/or utilisations of mass spectrometry are described. Chapter 2 describes and benchmarks a metal oxide sensor (MOS) coupled to a standard GC-MS instrument. Testing this system to the headspace of 12 stool samples the sensor detected a mean 1.6 more peaks per sample then the MS. This superior sensitivity exhibited by the MOS sensor should allow for greater discriminatory abilities to differentiate samples into clinically relevant groups. It has become increasingly important to qualitatively and quantitatively assess the VCs for use in monitoring health. Chapter 3 describes a novel method for the quantification of VCs from the headspace of stool samples analysed using GC-MS is presented. Using 13C labelled carbon compounds as internal standards a method has been designed which quantifies the compounds within in the stool; 15 compounds were quantified. The EDX110 dressing has been developed by Edixomed Ltd; uses hydrogel technology to generate nitric oxide (NO) to enhance wound healing. A series of experiments first allowed for the development of a robust and reproducible method of real-time quantification. The effect of pH was assessed using citric acid buffered with sodium citrate, pH values 3, 3.6, 4.2, 4.8, 5.4, and 6.2 were all analysed. NO production showed an inverse correlation; pH 3 producing 81 µg of NO and pH 6.2 only producing 7 µg. Except for pH 3 nitrous acid (HONO) and nitrogen dioxide (NO2) remained relatively consistent across the pH values with a median 3 and 0.9 µg respectively. iii Table of Contents Aims and objectives ................................................................................................. 1 Chapter 1: A review of mass spectrometry (MS) for detection of volatile compounds (VCs) for biomedical applications. .................................................... 3 1.1.0 Introduction ..................................................................................................... 4 1.1.1 Introduction to mass spectrometry (MS) .................................................................................................. 5 1.2.0 Non-real-time mass spectrometry techniques.............................................. 7 1.2.1 Sample pre-concentrating methods ......................................................................................................... 7 1.2.2 Gas chromatography (GC) ....................................................................................................................... 11 1.2.3 Gas chromatography mass spectrometry (GC-MS). ............................................................................... 11 1.2.4 Gas chromatography tandem mass spectrometry (GC-MS-MS) ............................................................. 13 1.2.5 Gas chromatography time of flight mass spectrometry (GC-TOF-MS) ................................................... 14 1.2.6 Two-dimensional gas chromatography time of flight mass spectrometry (GC-GC-TOF-MS) ................. 16 1.2.7 Gas Chromatography-Sensor systems and sensor arrays for biomedical applications .......................... 17 1.2.8 Summary and comparison of non-real time techniques ........................................................................ 18 1.3.0 Real time mass spectrometry techniques ................................................... 19 1.3.1 Selected ion flow tube mass spectrometry (SIFT-MS) ............................................................................ 19 1.3.2 Proton transfer reaction mass spectrometry (PTR-MS) .......................................................................... 22 1.3.3 Proton transfer reaction time of flight mass spectrometry (PTR-TOF-MS) ............................................ 23 1.3.4 Field asymmetric Ion mobility mass spectrometry (FAIMS) ................................................................... 24 1.3.5 Summary and comparisons of real-time techniques .............................................................................. 26 1.4.0 Overview ........................................................................................................ 27 Chapter 2: Assessment of a combined gas chromatography mass spectrometer sensor (GC-MSS) system for detecting biologically relevant volatile compounds (VCs). .................................................................................... 29 2.1.0 Introduction ................................................................................................... 31 2.2.0 Methods ......................................................................................................... 32 2.2.1 Sensor preparation and sensor chamber ................................................................................................ 32 2.2.2 GC-MS and sensor setup ......................................................................................................................... 33 2.2.3 Standard solutions .................................................................................................................................. 33 2.2.4 Stool samples .......................................................................................................................................... 37 iv 2.2.5 Bacterial culture headspace analysis ...................................................................................................... 37 2.2.6 Analysis ................................................................................................................................................... 37 2.3.0 Results and discussion ................................................................................ 38 2.3.1 Results of the analysis of standard solutions .......................................................................................... 38 2.3.2 Stool Samples .......................................................................................................................................... 45 2.3.3 Bacterial headspace analysis .................................................................................................................. 56 2.4.0 Conclusions ................................................................................................... 67 Chapter 3: Gas Chromatography Mass Spectrometry (GC-MS) Quantification of Metabolites in Stool Using 13C Labelled Compounds ......................................... 69 3.1.0 Introduction ................................................................................................... 71 3.2.0. Materials and methods ................................................................................ 73 3.2.1 Instrumentation and separation methodology ...................................................................................... 73 3.2.2 Loading the thermal desorption (TD) tubes ............................................................................................ 73 3.2.3 Standard Solutions .................................................................................................................................. 74 3.2.4 Calibration Curves ................................................................................................................................... 75 3.2.5 Sample Preparation ...............................................................................................................................
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