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In September 2020, traces of ethylene oxide (a toxic substance used as a pesticide in developing countries but banned for use on food items within the European Union) were found in foodstuffs containing ingredients derived from imported sesame seed products. Vast numbers of foodstuffs were recalled across Europe due to this contamination, leading to expensive market losses and extensive trace exposure of ethylene oxide to consumers. Therefore, a rapid analysis method is needed to ensure food safety by high-throughput screening for ethylene oxide contamination. Selected ion flow tube mass spectrometry (SIFT-MS) is a suitable method for rapid quantification of trace amounts of vapours in the headspace of food samples. It turns out, however, that the presence of acetaldehyde complicates SIFT-MS analyses of its isomer ethylene oxide. It was proposed that a combination of the H3O+and NO+reagent ions can be used to analyse ethylene oxide in the presence of acetaldehyde. This method is, however, not robust because of the product ion overlaps and potential interferences from other matrix species. Thus, we studied the kinetics of the reactions of the H3O+, NO+, OH−and O− ions with these two compounds and obtained their rate coefficients and product ion branching ratios. Interpretation of these experimental data revealed that the OH−anions are the most suitable SIFT-MS reagents because the product ions of their reactions with acetaldehyde (CH2CHO−at m/z43) and ethylene oxide (C2H3O2−at m/z59) do not overlap.

Selected ion flow tube mass spectrometry (SIFT-MS) instruments have significantly developed since this technique was introduced more than 20 years ago. Most studies of the ion–molecule reaction kinetics that are essential for accurate analyses of trace gases and vapors in air and breath were conducted in He carrier gas at 300 K, while the new SIFT-MS instruments (optimized to quantify concentrations down to parts per trillion by volume) operate with N2carrier gas at 393 K. Thus, we pose the question of how to reuse the data from the extensive body of previous literature using He at room temperature in the new instruments operating with N2carrier gas at elevated temperatures. Experimentally, we found the product ions to be qualitatively similar, although there were differences in the branching ratios, and some reaction rate coefficients were lower in the heated N2carrier gas. The differences in the reaction kinetics may be attributed to temperature, an electric field in the current flow tubes, and the change from He to N2carrier gas. These results highlight the importance of adopting an updated reaction kinetics library that accounts for the new instruments’ specific conditions. In conclusion, almost all previous rate coefficients may be used after adjustment for higher temperatures, while some product ion branching ratios need to be updated.