Dimethylsulphoxide (DMSO) in biological samples: A comparison of the TiCl 3 and NaBH 4 reduction methods using headspace analysis E.S.M. Deschaseaux a,b,c, ⁎, R.P. Kiene d,e , G.B. Jones a,b , M.A. Deseo a,f , H.B. Swan a,g , L. Oswald d,e,1 , B.D. Eyre a,c a School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW, Australia b Marine Ecology Research Centre, Southern Cross University, Lismore, NSW, Australia c Centre for Coastal Biogeochemistry, Southern Cross University, Lismore, NSW, Australia d Dauphin Island Sea Laboratory, Dauphin Island, AL, USA e Department of Marine Sciences, University of South Alabama, AL, USA f Southern Cross Plant Science, Southern Cross University, Lismore, NSW, Australia g National Measurement Institute, Chemical and Biological Metrology, North Ryde, NSW, Australia abstract article info Article history: Received 30 August 2013 Received in revised form 13 April 2014 Accepted 8 May 2014 Available online 22 May 2014 Keywords: DMSO TiCl 3 NaBH 4 Corals Macroalgae Dimethylsulphoxide (DMSO) is a sulphur compound that can result from the oxidation of biogenic dimethylsulphide (DMS) in marine algae and bacteria; with dimethylsulphoniopropionate (DMSP) being the main precursor of DMS. The two most commonly used methods for the analysis of DMSO in seawater and biolog- ical samples consist of its chemical reduction to DMS by either titanium trichloride (TiCl 3 ) or sodium borohydride (NaBH 4 ), with subsequent measurement of derived DMS by gas chromatography. Here, these two methods have been compared for the quantitative analysis of DMSO in the zooxanthellate coral Acropora aspera and in two species of marine algae (Ulva intestinalis and Ulva lactuca) using headspace analysis on DMSO-derived DMS. Reduction by NaBH 4 or TiCl 3 in biological samples yielded highly linear calibrations (R 2 ≥ 0.99) and excellent repeatability (RSD = 6.17% and 4.32% for TiCl 3 and NaBH 4 respectively, n = 10). In coral samples, although a strong linear correlation was generally obtained between the two reduction methods (R 2 = 0.8464, p b 0.001, n = 72), the regression slope of 0.6 indicated that DMSO concentrations were either underestimated with NaBH 4 reduction or overestimated with TiCl 3 . Reduction with TiCl 3 yielded lower values than NaBH 4 at DMSO concentrations b 0.6 μM, whereas TiCl 3 gave higher values than NaBH 4 when DMSO was N 2 μM. The reasons for these significant differences remain unclear at this stage and we therefore cannot draw conclusions on the preferential suitability of one reducing agent over the other for coral DMSO analysis. In macroalgae samples, significantly lower DMSO concentrations were obtained with NaBH 4 than with TiCl 3 for DMSO concentrations averaging 0.6 μM and 0.8 μM for U. intestinalis and U. lactuca respectively. The difference between reduction methods in the analysis of DMSO across macroalgae and coral samples was interpreted as a difference in taxa or in sample preparation, although this needs to be further investigated. Corals were found to contain more DMSO than macroalgae with similar DMSP concentrations. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Dimethylsulphoxide (DMSO) was reported for the first time in the marine environment in 1980 (Andreae, 1980) and was later identified as the most dominant dissolved dimethylated sulphur species in the Mediterranean Sea (Simό et al., 1997). Whilst several studies have report- ed higher concentrations of DMSO than those of both dimethylsulphide (DMS) or dimethylsulphoniopropionate (DMSP) (Hatton et al., 1996; Simό et al., 1997), other studies have shown that DMSO concentrations were lower than those of DMS and DMSP in seawater (Gibson et al., 1990). However, such differences in the proportions of these sulphur compounds could be explained by diurnal and seasonal variations of DMSO (Lee and de Mora, 1999). Marine DMSO was initially thought to be derived mainly from the photo-oxidation of DMS in the euphotic zone of the water column (Brimblecombe and Shooter, 1986); however marine bacteria were later found to play an important role in this reaction (Hatton et al., 2012). Other studies have demonstrated the presence of particulate (cellular) DMSO in phytoplankton (Hatton and Wilson, 2007; Simό et al., 1998), indicating that this oxidised sulphur species is also Marine Chemistry 164 (2014) 9–15 ⁎ Corresponding author at: School of Environment Science and Engineering, Southern Cross University, Military Road, Lismore NSW 2480, Australia. Tel.: +61 2 6620 3815; fax: +61 2 6621 2669. E-mail addresses: elisabeth.deschaseaux@gmail.com, e.deschaseaux.10@student.scu.edu.au (E.S.M. Deschaseaux), rkiene@disl.org (R.P. Kiene), graham.jones@scu.edu.au (G.B. Jones), myrna.deseo@scu.edu.au (M.A. Deseo), hilton.swan@measurement.gov.au (H.B. Swan), loswald@gmail.com (L. Oswald), bradley.eyre@scu.edu.au (B.D. Eyre). 1 Present address: United States Department of Agriculture, Agriculture Research Service, Florence, SC 29501, USA. http://dx.doi.org/10.1016/j.marchem.2014.05.004 0304-4203/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Marine Chemistry journal homepage: www.elsevier.com/locate/marchem