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SCS2022: Improving mass spectrometry – droplet by droplet

Graham Cooks. Photo: Purdue University

Graham Cooks is one of the plenary speakers at the second national meeting of the Swedish Chemical Society, SCS 2022, which takes place in Linköping on the 20-22nd of June. He is a Henry B. Hass Distinguished Professor in analytical chemistry at Purdue University in Indiana, USA, and during the event, he will be awarded the Torbern Bergman medal “for his groundbreaking contributions in the development and use of new analytical tools, especially within the field of mass spectrometry”.

– I work on mass spectrometry (MS) which is not a spectroscopic technique, in spite of its name. It deals with real matter, not radiation, says Graham Cooks.

In his research, he has had a special interest in synthesis using ions as reagents.

– Early experiments showed that molecular ions could be collected by a method that we termed ion soft landing. This can be used to deposit thin films on surfaces or to make new materials by reacting them as they land.

– An example of ion-based synthesis closer to organic chemistry is found in microdroplets. The starting point for most MS analysis is generation of ions by electrospray ionization (ESI).

He explains that the analysis goes wrong if the solvated ions in the droplets start to react.

– Fully solvated ions are slow to react but ions on droplet surfaces may react fast. So small droplets, with high surface/volume ratios favor reaction. Intriguingly, over the past decade, my group has identified and elaborated the phenomenon of reaction acceleration in microdroplets. The increase in rate constant (relative to bulk reactions) is inversely dependent on droplet size and factors of more than 105 proved to be common for a range of ordinary reactions.

– There were several consequences of this super-reactivity. Products are formed in microdroplets of reagents as they fly (millisecond times) to a mass spectrometer. This means that high throughput measurements of reactions in nanovolumes can be followed at rates of 1 sample/second in arrays of 6144 samples using automated MS equipment. Reaction acceleration allows small scale synthesis, simply by collecting the small droplets. This high throughput (HT) synthesis can be followed by equally HT bioassays, including enzyme kinetic measurements. This instrumentation facilitates drug discovery through HT reaction screening to optimize reactions, HT synthesis and then HT bioassays.

Graham Cooks encountered mass spectrometry through a visit to South Africa by Carl Djerassi.

– Complex mixture analysis by MS has been a theme of my research and this has involved building early tandem, miniature and hybrid mass spectrometers. My lab has also developed a variety of ambient ionization methods (DESI, paper spray, etc.) and used them for point-of-care surgical analysis, for chirality and thermochemical determinations, and for trace organic analysis.

Take the opportunity to listen to Graham Cooks and many other top scientists at the SCS2022 meeting in Linköping on the 20-22nd of June. The conference will bring together chemists from all fields of chemistry represented within the Swedish Chemical Society (Svenska Kemisamfundet).

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