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SRI Options

H3O+, NO+ and NH4+, O2+ / Kr+, Xe+ precursor ions.

Quantify more volatile compounds than ever in real-time with IONICON PTR-MS and SRI-MS technology, using the SRI/SRI+ features, and take advantage of single-digit pptv-level detection limits, only available with IONICON real-time trace gas analyzers.

Order your new IONICON PTR-MS with Switchable Reagent Ions capabilities or consult with us concerning upgrade capabilities of your instrument.

Advantages of using NO+, O2+ and NH4+ as precursor ions

H3O+ is ideal for many applications as our customers have proven for more than a decade. In some cases however it can be useful to use more than one reagent ion in your PTR-MS.

By using SRI several isomeric VOC compounds can be separated and instantaneously quantified (the differentiation of isobaric compounds is already possible by using IONICON PTR-TOFMS series).

NO+ is like H3O+ a soft ionizer, ionization occurs mainly through charge transfer, whereas O2+ is found to be a less soft chemical ionization agent and can be used where proton transfer from H3O+ does not work.

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 (patent pending).

Advantages of using Kr+ and Xe+ as precursor ions
Another revolutionary development is the implementation of Kr+ and Xe+ as reagent ions, made available as the optional SRI+ feature for IONICON PTR-MS instruments (US Pat. 9,188,564, EP 2606505 A1).

These reagent ions (Kr+ in particular) possess even higher ionization energies than O2+ and therefore also very important (inorganic) substances such as CH4, CO, CO2, NO2, SO2, etc. can be detected and quantified using a single IONICON instrument.

Learn more about Selective Reagent Ionization - Mass Spectrometry (SRI/SRI+) and download the new brochure:
Selective Reagent Ionization - Mass Spectrometry (SRI-MS) technology incl. SRI/SRI+ feature (0.2 MB .pdf)