Synthesis of reference organosulfates and optimization of UPLC-ESI-MS/MS method for their quantification in environmental samples: Its application for determination of organosulfates in PM_2.5

Abstract. We synthesized five organosulfates (OSs): ethyl-, 3-methylbenzyl-, cyclohexyl-, benzyl- and phenethyl sulfate, with four commercial authentic OSs: methyl-, phenyl-, octal-, and 4-nitrophenyl sulfate to use as reference standards for quantifying the OSs in environmental samples, using ultra-high performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS). The target OSs were separated using HSS T3 column with gradient flow of mobile phase consisting of pure water (H₂O) and methanol (CH₃OH) with 0.1 % formic acid. Characteristic ion fragments: phenolate anion (m/z 93) for phenyl sulfate, sulfate radical anion (•SO₄⁻, m/z 96) for methyl-, benzyl-, 3-methylbenzyl- and phenethyl-sulfate, and hydrogen sulfate anion (HSO₄⁻, m/z 97) for ethyl-, cyclohexyl- and octyl-sulfate were identified. In addition, the sulfite radical (•SO₃⁻, m/z 80) was observed for methyl-, ethyl-, phenyl-, cyclohexyl-, 3-methylbenzyl- and octyl-sulfate. The characteristic fragment ions utilized for quantification enhanced the identification of target compounds, and the limits of detection and quantification were 0.10 ng mL⁻¹ and 0.10-0.50 ng ml⁻¹. The optimized UPLC-ESI-MS/MS method was successfully applied for the determination of various OSs in PM_2.5 collected from Tianjin, China. Benzyl sulfate (7.05 ± 5.43 ng m⁻³) found to be the most abundant species followed by phenyl sulfate (4.65 ± 6.82 ng m⁻³), octyl sulfate and methyl sulfate in Tianjin PM_2.5.