Borohydride-Coupled HPLC-FPD Instrumentation and Its Use in the Determination of Dimethylsulfonium Compounds

Novel HPLC instrumentation has been developed which employs an in-line sodium tetrahydroborate (borohydride) reaction step to generate volatile sulfur species from a variety of sulfonium compounds. Transfer of the resulting volatile sulfur-containing products into the gas phase permits them to be monitored using sulfur-specific flame photometric detection. The system has been evaluated for the determination of a collection of dimethylsulfonium compounds, comprising (dimethylsulfonio)propionate, S-methylmethionine (SMM), (dimethylsulfonio)-2-methylpropionate, dimethylsulfocholine, (dimethylsulfonio)acetate, (dimethylsulfonio)butanoate, and (dimethylsulfonio)pentanoate. Following their separation by either cation- or anion-exchange HPLC, these compounds react in-line with the tetrahydroborate, generating dimethyl sulfide, which is then swept into a flame photometric detector. The development of chromatographic conditions for the resolution of the seven sulfonium compounds is described. In an example application of the instrumentation, the levels of SMM in parsley and cabbage were found to be 16 and 74 mmol kg(-)(1), respectively, on a fresh weight basis.