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Note: Solvent-mediated chemical ionization (SMCI) with propylamine is primarily intended for dedicated research instruments. Because propylamine has a very high proton affinity, it can strongly adsorb to surfaces and contaminate the chemical ionization gas delivery system. On many modern GC-MS instruments, this can result in persistent carryover and may interfere with subsequent CI experiments using conventional reagent gases.
If SMCI is to be implemented routinely, a separate reagent delivery line that bypasses the instrument's standard gas flow control module is recommended. Ideally, this line should be capable of being isolated from the instrument and evacuated under vacuum when not in use to minimize contamination and preserve normal CI performance.
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Solvent Mediated Chemical Ionization (SMCI) using propylamine was shown by Eastman Chemical in their recent work to be useful in the ionization of Surfynol. This compound is very difficult to ionize with many gasses showing the loss of water and no molecular weight information. The propylamine was found to offer similar useful molecular weight information which normally required the use of either ammonia and methylamine as shown in previous work at Eastman.
SMCI was originally demonstrated by Shimadzu in a poster session, to be a very convenient means for substituting liquids as chemical ionization reagents for GC-MS. Gases in lecture bottles are often inconvenient to purchase, somewhat hazardous to use, and often very difficult to dispose of when spent. NOTE: Ammonia gas if not used properly can be delivered to the MS source as a liquid (see link: Ammonia Gas Connection on 1st page) !
Other possibilities to try would be solutions of methylamine and ammonia in methanol that can be purchased from Aldrich, methanol-d4, ammonium hydroxide, deuterium oxide, propylamine in methanol-d4, etc. Of course, one could also do negative ion chemical ionization with a variety of solvents to get M-H or chloride adducts. The possibilities are somewhat endless depending on the class of compounds and their relative proton affinities using either pure solvents or mixtures taking into account their relative proton affinities.