Suppressor and calibration standard limitations in cation chromatography of ammonium and 10 alkylamines in atmospheric samples

Abstract

Ammonia (NH₃) and alkylamines are ubiquitous in the atmosphere and have been suggested to play important global roles through new particle formation and aerosol growth. In this work, we optimized an ion-chromatographic (IC) method to separate and quantify the ten most abundant atmospheric alkylamines with high selectivity and separation efficiency, using 4 μm packed columns and resin-based suppressors, alongside stabilizing amine standards. Modern resin suppressors operating on a gradient elution program affected the linear response of this IC technique. Calibration statistical analyses found a loss of analytes in these cation-exchange devices. Suppressor operational longevity was optimized by using a stepped current and an external water supply, which improved precision, accuracy, and LODs compared to other suppression modes. When this new method was applied to real samples, amines were found ubiquitously in size-resolved marine aerosol samples; monopropylamine, isomonopropylamine, and monobutylamine were detected and quantified, which have not been reported before. The molar ratio of the sum of aminium to ammonium ranged from 0.02 to 0.2, showcasing the application of the developed method towards studying the diversity and importance of alkylamines in coastal marine particle composition. The new analytical method also found NH₃ present in a suite of new homes with a mean mixing ratio of 25 ± 15 ppbv; a common level reached between homes across the study during the first year of occupation which can then be transported outdoors.