We developed a novel method of producing NH4+ solely from H2O vapor and N2 (gas cylinder or filtered air) in the established hollow cathode ion source, without the need of any ammonia, by adjusting the pressure and electric fields in the source (PCT application submitted). That is, the reagent ions can be rapidly switched.
Disadvantages of “classic” NH4+ ion production in IMR-MS instruments
Until now in order to produce NH4+ reagent ions IMR-MS instruments had to use NH3 gas cylinders or ammonia solutions as a NH3 source. The first approach requires a high level of safety precautions and is prohibited in some areas, the latter does not provide a stable NH3 concentration over time. Moreover NH3 can damage important parts of the instrument, such as lines, lenses, vacuum pumps, valves, flow controllers, etc. The instrument’s exhaust is contaminated with toxic NH3 and surfaces inside the IMR-MS instrument get covered with NH3 which desorbs very slowly after switching to a different reagent ion, i.e. switching from NH4+ to H3O+ takes tens of minutes if not hours.