Quantitation of 11 alkylamines in atmospheric samples: separating structural isomers by ion chromatography

Abstract. Amines are important drivers in particle formation and growth, which have 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 alkylamines (monomethylamine (MMAH⁺), dimethylamine (DMAH⁺), trimethylamine (TMAH⁺), monoethylamine (MEAH⁺), diethylamine (DEAH⁺), triethylamine (TEAH⁺), monopropylamine (MPAH⁺), isomonopropylamine (iMPAH⁺), and monobutylamine (MBAH⁺)) and two alkyl diamines (1, 4-diaminobutane (DABH⁺) and 1, 5-diaminopentane (DAPH⁺)). Further, the developed method separates the suite of amines from five common atmospheric inorganic cations (Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺). All 16 cations are greater than 95 % baseline resolved and elute in a runtime of 35 min. This paper describes the first successful separation of DEAH⁺ and TMAH⁺ by IC and achieves separation between three sets of structural isomers, providing specificity not possible by mass spectrometry. The method detection limits for the alkylamines are in the picogram per injection range and the method precision (±1σ) 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. In extracts of a size-resolved BB sample from an aged plume, we detected and quantified MMAH⁺, DMAH⁺, TMAH⁺, MEAH⁺, DEAH⁺, and TEAH⁺ in the presence of Na⁺, NH₄⁺, and K⁺ at molar ratios of amine to inorganic cation ranging from 1 : 2 to 1 : 1000. Quantities of DEAH⁺ and DMAH⁺ of 0.2–200 and 3–1200 ng m⁻³, respectively, were present in the extracts and an unprecedented amine-to-ammonium molar ratio greater than 1 was observed in particles with diameters spanning 56–180 nm. Extracts of respirable fine-mode particles (PM_2. 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 amine-to-ammonium ratio in a time series of samples never exceeded 0.15 during the sampling of the plume. These results and an amine standard addition demonstrate the robustness and sensitivity of the developed method when applied to the complex matrix of BB particle samples. The detection of multiple alkylamines in the analyzed BB samples indicates that this speciation and quantitation approach can be used to constrain BB emission estimates and the biogeochemical cycling of these reduced nitrogen species.