Figure 1: Schematic representation of the quantification procedure proposed in this study. From a filtered sample, three direct spectrophotometric spectra are acquired in three different buffered media (N, pH = 9.2; AC, pH = 4.7; and H, pH = 1.0) in the range 220–300 nm. Spectra are differentiated to the second degree (N″, AC″, and H″), and values of second derivative absorbance are extracted at specific wavelengths (N″250, AC″250 at 250 nm, and H″278 at 278 nm). These values can be used to directly quantify total thiosulfate (H2S2O3/HS2O3/S2O32−) and sulfite (SO2/HSO3/SO32−) contents, or, after subtraction, total sulfide concentration (H2S/HS/S2−).