Determination of atmospheric organosulfates using HILIC chromatography with MS detection

Abstract

Abstract. Measurements of organosulfates in ambient aerosols provide insight to the extent of secondary organic aerosol (SOA) formation from mixtures of biogenic gases and anthropogenic pollutants. Organosulfates have, however, proved analytically challenging to measure. This study presents a sensitive new analytical method for the quantification of organosulfates based upon ultra-performance liquid chromatography with negative electrospray ionization mass spectrometry (UPLC-ESI-MS/MS). The separation is based upon hydrophilic interaction liquid chromatography (HILIC) with an amide stationary phase that provides excellent retention of carboxy-organosulfates and methyltetrol-derived organosulfates. The method is validated using six model compounds: methyl sulfate, ethyl sulfate, benzyl sulfate, hydroxyacetone sulfate, lactic acid sulfate, and glycolic acid sulfate. A straightforward protocol for preparation of highly pure organosulfate potassium salts for use as quantification standards is presented. This highly efficient method of separating and quantifying organosulfates is used to evaluate the efficiency and precision of two methods of ambient PM2.5 sample extraction. Spike recoveries averaged 98 ± 8% for extraction by sonication and 98 ± 10% for extraction by rotary-shaking. Sonication was determined to be the superior method for its better precision. Analysis of ambient PM2.5 samples collected 10–11 July 2013 in Centreville, AL, USA during the Southeast Atmosphere Study (SAS) confirms the presence of hydroxyacetone sulfate in ambient aerosol for the first time. Glycolic acid sulfate was the most abundant compound measured (ranging 8–14 ng m−3), followed by hydroxyl acetone sulfate (2.7–5.8 ng m−3) and lactic acid sulfate (1.4–2.9 ng m−3). Trace amounts of methyl sulfate were detected, while ethyl sulfate and benzyl sulfate were not detected. Future research will focus on the development of additional organosulfates standards, expansion of this UPLC-MS/MS to include more target molecules, and the application of this method to assess temporal variations in organosulfates in ambient environments.

Quantifying organic matter and functional groups in particulate matter filter samples from the southeastern United States, part I: Methods

“…Mass contributions from organic S and N compromise a smaller portion of ambient OM (Liu et al, 2009;Stone et al, 2012) and were not included in this work. Substantial contributions of organosulfates to southeastern aerosol composition are possible (Hettiyadura et al, 2014), and the OM/OC ratios of small organosulfate molecules are high, therefore, future models may 20 consider such chemicals. The following paragraphs outline the atmospheric relevance and spectral features of each functional group reported in the current models.…”