Chemical ionisation mass spectrometry for the measurement of atmospheric amines

We describe a chemical ionisation mass spectrometer (CIMS) for the ambient measurement of amines, known as important gas-phase precursors for secondary aerosol formation. Protonated ethanol or acetone ions were used as ionisation reagents to selectively detect high proton affinity base compounds (e.g. amines and ammonia), thereby minimising interferences from other atmospheric gaseous organic compounds. With ethanol as ionisation reagent (300,000 Hz of ion signals), the CIMS showed similar sensitivities (2.1-8.7 Hz per pptv) and detection limits (7-41 pptv with a 1-min integration time) for ammonia and several atmospherically relevant key amine compounds containing one to six carbon atoms (C1- to C6- amines and their isomers). The CIMS background signals of the six amines ranged from 9 to 40 pptv, much lower than 930 pptv for ammonia. The CIMS response times were between 13 and 26 s for these amines. The unique combination of the fast time response, high sensitivities and low detection limits allows the use of this CIMS for real time measurements of atmospheric trace amines. During the ambient measurement made in Kent, OH, in November 2011, the measured mixing ratios of C2- and C3-amines were 8 pptv and 16 pptv, whereas those of ammonia were 517 pptv.