From PTR-MS to SRI-MS
SRI-MS is a proprietary technology where the user can select from different reagent ions for chemical ionization direct injection mass spectrometry, only available from IONICON.
Our expertise in ion chemistry, being as the world's leading PTR-MS company, lead to the development of new ionization technologies currently including H3O+, O2+, NO+, NH4+, Kr+ or Xe+ as selective reagent ions.
SRI-MS instruments can be ordered with your individual choice of reagent ions but in generel the basic configuration offered is a PTR-MS instrument (using H3O+ as reagent ion) with optional SRI and SRI+ configurations. Available for all new or as upgrades of existing PTR-MS systems.
With SRI you can choose between NO+, O2+ and NH4+ as additional reagent ions. Using NO+ enables separating many isomeric compounds and thus allowing for detecting and quantifying them independently. O2+ possesses an ionization energy (IE) of 12.1 eV, which is considerably higher than the IE of NO (9.3 eV) and can therefore ionize substance classes that are not detectable via CTR from NO+ or even PTR ionization from H3O+. However, the IE is still below the IE of common air compounds and therefore no diluting buffer gas is needed. NH4+ reagent ions are particularly beneficial in complex mass spectra because of higher sensitivity (less fragmentation) and higher selectivity (higher proton affinity). We developed a unique method for fast switching to/from NH4+ reagent ions without adding ammonia (US Pat 11,342,171, EP 3503161 B1, CN 111,386,590 A).
For SRI+ the available reagent ions are extended to Xe+ and Kr+. Xenon has an IE of 12.1 eV, i.e. the IE is very similar to the IE of O2. Therefore this reagent ion can be used as a substitute for O2+ in environments where no oxygen cylinders are allowed (e.g. due to fire protection or ex-proof laws). Krypton, on the other hand, has an IE of 14.0 eV, i.e. well above all reagent ions utilized in PTR-MS instruments so far. According to the National Institute of Standards and Technology (NIST) there are only 18 compounds possessing a higher IE than Kr, thus it can be said that Kr+ is transforming an IONICON PTR-MS instrument into a universal trace gas analyzer (US Pat. 9,188,564, EP 2606505 A1).