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

Abstract

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 85-117 %. 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 0.1-17.8 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.

Analytical methodologies for oxidized organic compounds in the atmosphere

“…Ultrasound-assisted extractions (UAE) have been very common, 34,38,64,86 but mechanical extraction with an orbital shaker or by vortexing has also been employed providing good and quantitative recoveries. 2,66 Albinet et al 97 compared MeOH extractions using UAE and vortexing for the assessment of reference concentrations for 12 SOA markers in an urban dust standard reference material (SRM 1649b, NIST). Similar concentrations were obtained with both extraction techniques, and the reference values determined in the study made it possible to evaluate the efficiency of the extractions in a later study.…”

“…38 The smallest and highly polar organic acids, on the other hand, have been analyzed by ion chromatography (IC). Kwiezinski et al 2 employed an IC-MS method employing an anion exchange column to determine oxalic acid, glycolic acid, malic acid, and citric acid with LODs of 2.5–10 μg L −1 and more hydrophobic acids with five and ten times lower detection limits. Carbohydrates, 2-MEs and other sugar alcohols have been analyzed by high performance anion exchange chromatography (HPAEC).…”

“…LC-MS methods have given LOD values from extracts between 0.1 and 10 ng mL −1 for organic acids and 0.075–4 ng mL −1 for organosulfate compounds. 2,38 LODs of 1–25 ng mL −1 have been obtained for carbohydrates by LC-MS. 30…”

“…2,30,38,64 Positive mode ESI is applicable for detection of carbohydrates. 30 Compared to other LC works, the IC-ESI-MS configuration employed by Kwiezinski et al 2 required a separate suppressor and post-column addition of iso-propanol to avoid non-volatile salt stacking in the ion source and to increase the sensitivity, as the eluent was an aqueous solution of potassium hydroxide. With CI employing ammonia and isobutane, it has been possible to detect DNPH derivatives of carbonyls, hydroxyl group compounds derived with 4-nitrobenzonyl chloride, and organic acids derived with 2-nitrophenylhydrazine hydrochloride using positive polarity.…”

“…9,36,68 For accurate identifications of compounds, HR-MS is required to determine the elemental composition or to provide more selective detection of analytes. For those purposes, the most commonly employed HR-MS analyzer has been Orbitrap 2,36 or time of flight (TOF) which has been employed as alone or in combination with a quadrupole (Q-TOF). 38,86,87,100,101 This tandem mass spectrometry (MS/MS) has also been established by coupling three quadrupoles.…”