Fast Determination of the Main Reduced Sulfur Species in Aquatic Systems by a Direct and Second-Derivative Spectrophotometric Method

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⁻).