Quantitation of nine alkyl amines in atmospheric samples: Separating structural isomers by ion chromatography

Abstract

Abstract. Amines are important drivers in particle formation and growth, which has implications for Earth’s climate. In this work, we developed an ion chromatographic (IC) method using sample cation-exchange preconcentration for separating and quantifying the nine most abundant atmospheric alkyl amines (monomethylamine (MMAH+), dimethylamine (DMAH+), trimethylamine (TMAH+), monoethylamine (MEAH+), diethylamine (DEAH+), triethylamine (TEAH+), monopropylamine (MPAH+), isomonopropylamine (iMPAH+), and monobutylamine (MBAH+)). Further, the developed method separates the suite of amines from five common atmospheric inorganic cations (Na+, NH4+, K+, Mg2+, Ca2+). All 14 cations are greater than 95 % baseline resolved and elute in a runtime of 35 minutes. This paper describes the first successful separation of DEAH+ and TMAH+ by IC and achieves separation between three structural isomer pairs, providing specificity not possible by mass spectrometry. The method detection limits for the alkyl amines are in the picogram per injection range and the method precision (+1 σ) analyzed over 3 months was within 16 % for all the cations. The performance of the IC method for atmospheric application was tested with biomass-burning (BB) particle extracts collected from two forest fire plumes in Canada with large loadings of K+. In extracts of size-resolved BB samples from an aged plume we detected and quantified MMAH+, DMAH+, TMAH+, MEAH+, DEAH+ and TEAH+ in the presence of Na+, NH4+, and K+ at amines to inorganic cations molar ratios ranging from 1 : 2 to 1 : 1000. Quantities of DEAH+ and DMAH+ of 0.2–200 ng m−3 and 3–1200 ng m−3, respectively, were present in the extracts and an unprecedented amines to ammonium molar ratio greater than one was observed in particles with diameters spanning 56–180 nm. Extracts of respirable fine mode particles (PM2.5) from a summer forest fire in British Columbia in 2015 were found to contain iMPAH+, TMAH+, DEAH+ and TEAH+ at molar ratios of 1 : 300 with the dominant cations. The amines to ammonium ratio in a time-series of samples never exceeded 0.15 during the sampling of the plume. These results demonstrate the robustness and sensitivity of the developed method when applied to the complex matrix of biomass burning particle samples. The detection of multiple alkyl amines in the analyzed BB samples indicates that this speciation and quantitation approach can be used to constrain BB emission inventories and the biogeochemical cycling of these reduced nitrogen species.