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 NH3), thereby minimising interferences from other atmospheric gaseous organic compounds. With ethanol as ionisation reagent (similar to 3 x 10(5) Hz of ion signals), the CIMS showed similar sensitivities (2.1-8.7 Hz pptv(-1)) and detection limits (7-41 pptv with a 1-min integration time) for NH3 and several atmospherically relevant key amine compounds containing one to six carbon atoms (C-1- to C-6-amines and their isomers). The CIMS background signals of the six amines ranged from 9 to 40 pptv, much lower than similar to 930 pptv for NH3. 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 C-2- and C-3-amines were 8 +/- 3 (mean +/- 1 standard deviation) and 16 +/- 7 pptv, whereas those of NH3 were 517 +/- 259 pptv.