Obituary: Professor David Smith.

Professor David Smith, PhD, FRS, passed away peacefully at home on 15 February 2023. Professor David Smith, one of nine children, was born 1935 in Stoke-on-Trent, UK. He was educated in physics and chemistry that resulted in his interest in gas discharge physics and this combined with a unique vision and inventiveness made him a leading figure in the experimental investigations of gas phase electron and ion chemistry. Among other achievements, he is known as the originator of the selected ion flow tube (SIFT) technique for the study of the kinetics of reactions of ions with molecules occurring in the interstellar space in the mid-1970s. Using this technique he studied with colleagues thousands of ion-molecule rate coefficients, most of which he kept in his phenomenal memory all of his life. This was a foundation for the development of the SIFT-MS analytical technique some 20 years later, which is now widely known in the breath gas community as one of the online tools for the quantification of breath gas constituents. In 1996, David wrote the first article detailing the utility of SIFT-MS for the quantitative and sensitive analysis of trace gases in breath. Today the breath gas literature is replete with articles reporting on breath-related studies employing SIFTMS. David Smith’s publications clearly illustrate his impact on the development of breath research over the past three decades. David was a founding member of the International Association of Breath Research (IABR), and a founding editorial board member of this journal. David’s unique contribution to breath analysis was his pioneering studies using SIFT-MS to measure the concentration of targeted volatile metabolites in breath in real-time. This approach provides quantitative information on the abundance of small molecules in breath that could not be observed in offline analyses of collected breath samples. His research was recognized nationally and internationally by many awards, notably election as a fellow of the Royal Society, London, UK,Honorary DSc, University of Keele, and most recently the Heyrovsky medal from the Czech Academy of Sciences. Additionally, a special issue of Journal of Breath Researchwas published in 2014 (J. BreathRes. 8 (2014) 030201) in recognition of David’s substantial contributions to the field of breath gas analysis. The breath research community will miss David for his unique contributions, critical approach to science, insight, vision and for his role in evocative discussions during international breath research meetings.