The sources, formation mechanism and amount of organosulfates (OS) in atmospheric aerosol are not yet well understood, partly due to the lack of authentic standards for quantification. In this study, we report an improved robust procedure for the synthesis of organosulfates with different functional groups. Nine authentic organosulfate standards were synthesized and four standards (benzyl sulfate, phenyl sulfate, glycolic acid sulfate, and hydroxyacetone sulfate) were used to quantify their ambient concentrations. The authentic standards and ambient aerosol samples were analyzed using an optimized ultra performance liquid chromatography-electrospray ionization-tandem mass spectrometric method (UPLC-ESI-MS/MS). The recovery ranged from 80.4 to 93.2 %, the limits of detection and limits of quantification obtained were 1.1-16.7 and 3.4-55.6 pg m(-3), respectively. Measurements of ambient aerosol particle samples collected in winter 2013/2014 in urban Xi'an, northwestern China, show that glycolic acid sulfate (77.3 +/- 49.2 ng m(-3)) is the most abundant species of the identified organosulfates followed by hydroxyacetone sulfate (1.3 +/- 0.5 ng m(-3)), phenyl sulfate (0.14 +/- 0.09 ng m(-3)), and benzyl sulfate (0.04 +/- 0.01 ng m(-3)). Except for hydroxyacetone sulfate, which seems to form mainly from biogenic emissions in this region, the organosulfates quantified during winter in Xi'an show an increasing trend with an increase in the mass concentrations of organic carbon indicating their anthropogenic origin.