Determination of highly polar compounds in atmospheric aerosol particles at ultra-trace levels using ion chromatography Orbitrap mass spectrometry

A method using ion chromatography coupled to high-resolution Orbitrap mass spectrometry was developed to quantify highly-polar organic compounds in aqueous filter extracts of atmospheric particles. In total, 43 compounds, including short-chain carboxylic acids, terpene-derived acids, organosulfates, and inorganic anions were separated within 33 min by a KOH gradient. Ionization by electrospray was maximized by adding 100 µL min^-1 isopropanol as post-column solvent and optimizing the ion source settings. Detection limits (S/N ≥ 3) were in the range of 0.075-25 μg L^-1 and better than previously reported for 22 compounds. Recoveries of extraction typically range from 85 to 117%. The developed method was applied to three ambient samples, including two arctic flight samples, and one sample from Melpitz, a continental backround research site. A total of 32 different compounds were identified for all samples. From the arctic flight samples, organic tracers could be quantified for the first time with concentrations ranging from 0.1 to 17.8 ng m^-3 . Due to the minimal sample preparation, the beneficial figures of merit, and the broad range of accessible compounds, including very polar ones, the new method offers advantages over existing ones and enables a detailed analysis of organic marker compounds in atmospheric aerosol particles.