A method using ultra-high performance liquid chromatography coupled to a high resolution Orbitrap mass spectrometer was developed to identify and quantify imidazoles in aqueous extracts of aerosol particles. The aqueous particle extract was used without further enrichment or sample clean-up. Five columns were tested for efficient separation of ten imidazoles and the Acquity HSS T3 column was chosen for further optimization. Low limits of detection (<25 nM) and good intraday and interday repeatability (<1.6 and <6%, respectively) were achieved. Investigation of matrix effects showed that external calibration is applicable when the loading of organic carbon in the sample is below 10 μg m −3 . The developed method was applied to ten real samples, and six out of the ten test imidazoles were successfully quantified, while six further imidazoles were qualitatively identified, among them 4-imidazolecarboxaldehyde and 4-methyl-5-imidazolecarboxaldehyde. Advantages of the method are the minimal sample preparation, the short run time for each sample, and the low detection limits. These allow for a fast and reliable quantification of imidazoles even in a large number of aqueous particle extract samples. K E Y W O R D Sbrown carbon, high resolution mass spectrometry, imidazoles, method development, organic aerosolsThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

DOI: https://doi.org/10.1002/jssc.201900689 The cover picture shows a schematic presentation of a new method to analyze imidazole compounds in ambientparticles. Aqueous particle extracts are prepared and subsequently analyzed by UHPLC‐Orbitrap‐MS. The extracted ion chromatogram shows the successful separation of the 10 model imidazoles with the final optimized method. Imidazoles found in ambient aerosol particles are indicated with their corresponding chemical structures.