Fast microplate assay for simultaneous determination of thiols and dissolved sulfides in wastewater

The present paper reports the development and the application of a microplate assay for the fast and individual determination of thiols and sulfides. The method is based on the reaction of ethyl propiolate with thiols and sulfides, yielding thioacrylates absorbing in the UV range. Thioacrylate generated by derivation of sulfide with EP presents a bathochromic shift of maximal absorbance wavelength of 16 nm compared to thioacrylates formed with thiols. EP concentration, reaction time and derivatization pH were carefully optimized in order to separately quantify thiols and sulfides using a spectral deconvolution procedure in 15 min. The detection limits were 0.6 and 2.8 μM (63.7 and 92.4 μg·L− 1) for mercaptopropionic acid (used as reference thiol compound for calibration) and dissolved hydrogen sulfide respectively. Non-thiol sulfur compounds (methionine, sulfates and sulfites) or other nucleophile compound did not display any interference in the determination of MPA or sulfides. Interference from metals was suppressed with application of a reduction step with TCEP and DTPA. Finally, the method has been successfully applied to the analysis of raw and treated wastewater.