Ambient pressure proton transfer mass spectrometry: detection of amines and ammonia

An instrument to detect gaseous amines and ammonia is described, and representative data from an urban site and a laboratory setting are presented. The instrument, an Ambient pressure Proton transfer Mass Spectrometer (AmPMS), consists of a chemical ionization and drift region at atmospheric pressure coupled to a standard quadrupole mass spectrometer. Calibrations show that AmPMS sensitivity is good for amines, and AmPMS backgrounds were suitably determined by diverting sampled air through a catalytic converter. In urban air at a site in Atlanta, amines were detected at subpptv levels for methyl and dimethyl amine which were generally at a low abundance of <1 and ∼3 pptv, respectively. Trimethyl amine (or isomers) was on average about 4 pptv in the morning and increased to 15 pptv in the afternoon, while triethyl amine (or isomers or amides) increased to 25 pptv on average in the late afternoon. The background levels for the 4 and 5 carbon amines and ammonia were high, and data are very limited for these species. Improvements in detecting amines and ammonia from a smog chamber were evident due to improvements in AmPMS background determination; notably dimethyl amine and its OH oxidation products were followed along with impurity ammonia and other species. Future work will focus on accurate calibration standards and on improving the sample gas inlet.