Alfons Jordan

1 Introduction Over the past few decades, developers of proton-transfer-reaction—mass spectrometry (PTR-MS) instruments have pursued two key objectives: improving sensitivity and selectivity. PTR-MS sensitivity is specified as the number of detected ion counts per second for 1 part-per-billion volume mixing ratio (cps/ppbv) of an analyte, typically in air.

Proton-transfer-reaction mass spectrometry (PTR-MS) is widely used for measuring organic trace gases in air. In traditional PTR-MS, both nonpolar and polar analytes are ionized with unit efficiency, as predicted from ion-molecule collision theories. This well-defined ion chemistry allows for direct quantification of analytes without prior calibration and therefore is an important characteristic of PTR-MS.