13 Apr 2016
John Wilkins has been a member of SCI since 1992 and he has been an active committee member with the Cambridge and Great Eastern committee since 2000, becoming chair in 2006 - a position he still holds today. John is a frequent contributor to SCI’s forums and has organised many events with the Cambridge and Great Eastern committee. Alongside John’s contributions to SCI, and his day job as an External Affairs Manager for Mologic, he has recently received his doctorate from Cardiff University. Here, John tells us a little more about the path he took to achieve his goal.
‘I was recently awarded a PhD in Analytical Chemistry. Its gestation was a little longer than normal. I originally registered at Cardiff University over 30 years ago. When I originally enrolled, I was working at the Harpenden Laboratory, a part of the Agricultural Development & Advisory Service (ADAS), which was within the Ministry of Agriculture, Fisheries & Food (MAFF) - now DEFRA. The Harpenden Laboratory contributed to the UK’s surveillance programmes for pesticide residues in foods. I was involved in using mass spectrometry to support this work. However, shortly after my enrolment, I moved to Unilever’s food research laboratories at Colworth House (Sherbrook, Bedford, UK), and I regret that my PhD studies fell by the wayside.
After Unilever, I moved into the biotechnology and immunodiagnostics sector with my friend and colleague Prof Paul Davis. At Mologic, we support several students. During a meeting concerning PhD studentships with Dr Ian Fallis, of the Cardiff Chemistry Department, I mentioned that I had registered at his university for an external PhD many years before, but had never submitted. His response was simple. ‘Just do it!’
With his support, I was able to re-enrol, and by reviewing my original data and several published papers, I was able to compile and successfully submit my thesis within 12 months. So my grateful thanks must go to Dr Ian Fallis and the Cardiff University Registry, for their patience and support.
Finally, my advice to any PhD students out there. Don’t wait as long as I did. Just do it!’
Dr John Wilkins
Chair, Cambridge and Great Eastern Group
The analysis of pesticides & related compounds using Mass Spectrometry.
John P. G. Wilkins
17 November 2015
ABSTRACT
The determination of pesticides and related materials in food and environmental samples is important and presents an enduring challenge to analytical chemists. For practicality it is important that as many pesticides as possible are compared using a common technique. Mass spectrometry is the method of choice for multi-residue detection techniques, because of its sensitivity and specificity. This thesis comprises a detailed analysis and critical review of the mass spectrometric behaviour of over 600 commonly encountered pesticides and related compounds.
The work described in this thesis was undertaken in two tranches, one old and one new. The former experimental work was performed during the author’s employment at the Ministry of Agriculture, Fisheries & Food (Harpenden, Hertfordshire, UK) and at Unilever Research (Colworth House, Sharnbrook, Bedfordshire, UK). The data helped underpin the analytical work of the UK national pesticide residues monitoring surveillance team and the pesticide formulations safety team. Qualitative and quantitative aspects were both important, e.g. for identification and characterisation of active ingredients, contaminants and degradation products in technical pesticide formulations, as well as unambiguous detection and/or confirmation of residue levels in UK fruit and vegetables. The latter experimental work was undertaken recently (2015) at the Cardiff School of Chemistry during the preparation of this thesis. The newly acquired data helped confirm the validity and robustness of the original data, and helped to better understand them.
Understanding the complex and sometimes unexpected behaviour of molecules during their extraction/analysis is essential, especially when performing trace analysis at the parts per billion level. Rationalisation of the mass spectrometric fragmentation pathways of these compounds was undertaken in order to better understand the fundamental processes taking place in the mass spectrometer. This improved understanding was essential in order to ensure the quality and validity of the data generated using these techniques. For comparison, some additional data are included, e.g. for chemical warfare agents, using literature data. Mass spectrometry was chosen because of its power as an analytical technique. General approaches and specific precautions which should be taken when using mass spectrometry for pesticide analysis are discussed and explained in this document and literature data were critically reviewed. It is hoped that these data and recommendations will find continued and future use as an adjunct to the plethora of literature data and MS instrument manufacturer databases.
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