How to Use Ion-Molecule Reaction Data Previously Obtained in Helium at 300 K in the New Generation of Selected Ion Flow Tube Mass Spectrometry Instruments Operating in Nitrogen at 393 K

Abstract

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 N2 carrier 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 N2 carrier 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 N2 carrier 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 N2 carrier 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.

Headspace-Selected Ion Flow Tube Mass Spectrometry Workflows for Rapid Screening and Quantitation of Hazardous Volatile Impurities in Personal Care Products

“…Preparation: Analyte Library Entry Optimization for the SIFT-MS Instrument Prior to any method creation in software (and hence before sample analysis), it is recommended that the library entries on the specific SIFT-MS instrument be checked-primarily in terms of giving a quantitative agreement across the reagent ion-product ion pairs for each analyte. The reason for doing this is that for some analytes, there can be minor variations from instrument to instrument, or from one instrument model to another, or between helium and nitrogen carrier gases [30]. Agreement between concentrations calculated from the primary product ions (the potential quantitation ions) in a clean matrix ensures that the results obtained on the product matrix during method development are of maximum value (e.g., related to decisions on specificity).…”