Advanced molecular-fingerprinting analysis of dissolved organic sulfur by electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry using optimal spray solvent

Molecular level characterization of dissolved organic sulfur(DOS)by electrospray ionizationFourier transform ion cyclotron resonance mass spectrometry(ESI-FTICR MS)is necessary for further understanding of the role of DOS in the environment.Here,ESI spray solvent,a key parameter for ion production during ESI process,was investigated for its effect on the molecular characterization of DOS by ESI-FTICR MS.100%MeOH as spray solvent was found for the first time to remarkably enhance the ionization efficiency of the majority of CHOS-molecules in NOM,which facilitated a total of 1473 CHOS-molecular formulas with one sulfur atom to be detected.The number of CHOS-molecular formulas obtained using 100%MeOH as spray solvent increased notably over 740 in comparison with those using 50%MeOH aqueous solution(731)or 50%ACN aqueous solution(653).Moreover,due to the enhancement of ionization efficiency of DOS during ESI processes,the tandem mass spectra of the NOM CHOS-molecules could be easily obtained using 100%MeOH as spray solvent,which were hardly obtained using 50%MeOH aqueous solution as spray solvent.The results of the tandem mass spectra suggested the first discovery of organosulfates or sulfonic acids in Suwannee River NOM sample.A simple method based on 100%MeOH as ESI spray solvent for advanced molecular characterization of DOS by ESI-FTICR MS was proposed and applied,and the results revealed more molecular information of DOS in sea DOM samples.

Dissolved organic sulfur in streams draining forested catchments in southern China

Dissolved organic sulfur （DOS） is an important fraction for sulfur mobilization in ecosystem. In this work stream waters were sampled in 25 forested sites in southern China to study the dissolved sulfur fractions. Dissolved sulfur was fractionated into dissolved organic sulfur （DOS） and inorganic sulfate （SO]-） for 95 stream water samples. The results showed that the concentration of DOS ranged from 0 to 13.1 mg/L （average 1,3 mg/L） in all the streams, High concentrations of DOS in stream waters were found in the sites with high concentrations of sulfate. DOS constituted less than 60.1% of dissolved sulfur （average 17.9%）. Statistical analysis showed that DOS concentration was correlated with SO42- in streams waters and total sulfur in surface layer soils. The results also showed that DOS concentration in stream waters had a seasonal variation, but no trends were found with it. The implication was that the long term sulfur deposition had led the increase of the concentration and fraction of DOS in stream waters in acid rain prevailing regions