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Atomic Structure and Mass Spectrometry

4. Ionisation

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About this Lecture


In this mini-lecture we look at the inner workings of a mass spectrometer, and how they are able to determine the mass of atoms and molecules. The function of mass spectrometers can be split into two parts: ionisation and time of flight. We start with ionisation, and the different techniques employed to place a charge on molecules and fragments of interest. The two most common methods are electrospray and electron ionisation, and we look at exactly how these methods function from start to finish. These are techniques used frequently in analytical laboratories, not just in academia or industry, but also in forensics and paleodietary studies as we will learn later.


In this course Professor James McCullagh (Oxford University) lectures on atomic structure and mass spectrometry, and how the two fields of research have been woven together for decades. What is an atom, and what is made of? These were the questions that perplexed physicists and chemists for decades, going through many iterations of theories. We begin (i) with the history of the atomic model, dating back from the Ancient Greeks all the way to modern science, learning the techniques scientists used to learn more about the atom; (ii) then learning how these tools developed into the first prototypes of mass spectrometers; (iii) and discussing what measurements of an atom were made when observing atoms in mass spectrometers, including atomic number, mass number and relative atomic mass; (iv) and how these values are determined in modern mass spectrometers by electrospray and electron ionisation; (v) then focusing on Time-of-Flight, the most common metric measured to determine the mass of a charged particle; (vi) then moving onto discussing how we interpret mass spectra; and (vii) the ways in which mass spectrometry is used in modern-day research chemistry, such as in paleodietary studies.


James McCullagh is Professor of Biological Chemistry and Director of the Mass Spectrometry Research Facility based in the Department of Chemistry. His research focusses on understanding the function of small molecules in biological, biomedical and environmental systems, with particular focus on metabolism and metabolomics. He has 20 years experience in the development of (bio)analytical chemistry techniques, in particular using mass spectrometry, with applications in chemical, biological and medical research. He is highly collaborative and works with academia and industry partners. He has authored/co-authored over 100 journal publications, book chapters and articles including a Mass Spectrometry textbook. He lectures on undergraduate and graduate analytical chemistry courses and runs workshops for post-graduate researchers in mass spectrometry methods, metabolomics, chemometrics and bioinformatics. He is a graduate (D.Phil.) and undergraduate (M.Chem.) supervisor. He has served on various national administrative and conference committees and provides consultancy in the field of mass spectrometry and bioanalytical science to a variety of commercial enterprises. He is currently Cell Metabolism section editor for the journal Metabolites and an editorial board member for the journal Scientific Reports. James McCullagh is also Director of the Mass Spectrometry Research Facility SRF, based in the Chemistry Research Laboratory, Department of Chemistry. This houses over £10 million in analytical instrumentation with 20 mass spectrometer systems supporting academic research. He manages a team of permanent mass spectrometry staff who provide analytical service provision for the Department, wider University and external organisations including industry.

Cite this Lecture

APA style

McCullagh, J. (2022, January 17). Atomic Structure and Mass Spectrometry - Ionisation [Video]. MASSOLIT.

MLA style

McCullagh, J. "Atomic Structure and Mass Spectrometry – Ionisation." MASSOLIT, uploaded by MASSOLIT, 17 Jan 2022,