Sulfur compounds are often present in petrochemical wastewater and can be detected by UV spectrophotometry. This technique allows to point out specific absorptions of mineral sulfide and mercaptans and can be used for the determination of acidity constants. From a quantitative point of view, using a spectral deconvolution method, a specific determination of some mercaptans is obtained. Detection limits for ethanethiol and thiophenol are 0.7 and 2.5 mg l(-1), respectively.