title: Rapid quantification and isotopic analysis of dissolved sulfur species.
abstract: BACKGROUND
  Dissolved sulfur species are of significant interest, both as important substrates for microbial activities and as key intermediaries in biogeochemical cycles. Species of intermediate oxidation state such as sulfite, thiosulfate, and thiols are of particular interest but are notoriously difficult to analyze, because of low concentrations and rapid oxidation during storage and analysis.
  
  
  METHODS
  Dissolved sulfur species are reacted with monobromobimane which yields a fluorescent bimane derivative that is stable to oxidation. Separation by Ultra-Performance Liquid Chromatography (UPLC) on a C18 column yields baseline resolution of analytes in under 5 min. Fluorescence detection (380 nm excitation, 480 nm emission) provides highly selective and sensitive quantitation, and Time-of-Flight Mass Spectrometry (TOF-MS) is used to quantify isotopic abundance, providing the ability to detect stable isotope tracers (either33S or34S).
  
  
  RESULTS
  Sulfite, thiosulfate, methanethiol, and bisulfide were quantified with on-column detection limits of picomoles (μM concentrations). Other sulfur species with unshared electrons are also amenable to analysis. TOF-MS detection of34S enrichment was accurate and precise to within 0.6% (relative) when sample and standard had similar isotope ratios, and was able to detect enrichments as small as 0.01 atom%. Accuracy was validated by comparison to isotope-ratio mass spectrometry. Four example applications are provided to demonstrate the utility of this method.
  
  
  CONCLUSIONS
  Derivatization of aqueous sulfur species with bromobimane is easily accomplished in the field, and protects analytes from oxidation during storage. UPLC separation with fluorescence detection provides low-μM detection limits. Using high-resolution TOF-MS, accurate detection of as little as 0.01%34S label incorporation into multiple species is feasible. This provides a useful new analytical window into microbial sulfur cycling. Copyright © 2017 John Wiley & Sons, Ltd.
authors.affiliation: Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E California Blvd, Pasadena, CA, 91125, USA.
authors.forename: Derek A
authors.identifier: http://orcid.org/0000-0002-3675-9153
authors.initials: DA
authors.lastname: Smith
authors.affiliation: Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E California Blvd, Pasadena, CA, 91125, USA.
authors.forename: Alex L
authors.initials: AL
authors.lastname: Sessions
authors.affiliation: Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E California Blvd, Pasadena, CA, 91125, USA.
authors.forename: Katherine S
authors.initials: KS
authors.lastname: Dawson
authors.affiliation: Environmental Science and Engineering, California Institute of Technology, 1200 E California Blvd, Pasadena, CA, 91125, USA.
authors.forename: Nathan
authors.initials: N
authors.lastname: Dalleska
authors.affiliation: Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E California Blvd, Pasadena, CA, 91125, USA.
authors.forename: Victoria J
authors.initials: VJ
authors.lastname: Orphan