Improved cyanolysis protocol for detection of zero‐valent sulfur in natural aquatic systems

Abstract

We propose a novel protocol for detection of reactive zero-valent sulfur (ZVS) in natural aquatic samples including seawater. Reaction with hot potassium cyanide at slightly acidic conditions recovers ZVS from colloidal fraction of particulate elemental sulfur, polysulfides (S n 2-), and their protonated forms. Preconcentration by partial evaporation of the sample and separation of thiocyanate anions by high-performance liquid chromatography on the C30 reverse phase column modified with poly(ethylene glycol) followed by spectrophotometric detection at 220 nm wavelength allows us to detect reactive ZVS with detection limit of 3 nmol L -1 for fresh water samples and 6 nmol L -1 for seawater samples. Storage at 4°C for 6 weeks does not change the concentration of thiocyanate in the sample by more than 10%.

Quantification of free and metal-complexed cyanide by tetrathionate derivatization

“…Tetrathionate decomposes in aqueous solutions at near neutral pH to lower and higher polythionates [21 and references therein]. Pentathionate elutes before thiocyanate with less than a 2 min difference in retention time [12]. At high pentathionate to thiocyanate ratios precise integration of the thiocyanate peak becomes problematic.…”

“…Tetrathionate and higher polythionates react rapidly with cyanide (Equation (3)), and trithionate reacts with cyanide much slower (Equation (4)) [13-15 and references therein]. Colloidal and dissolved elemental sulfur is reactive toward cyanide as well (Equation (5)) [12,13].…”

“…Polysulfides react with cyanide in minutes to hours, depending on pH, at 25 C and in seconds to minutes at 100 C (Equation (1)) [10][11][12][13]. Thiosulfate reacts with cyanide three orders of magnitude slower than polysulfides (Equation (2)) [10].…”

Hydrogen Cyanide Accumulation and Transformations in Non-polluted Salt Marsh Sediments

“…Sulfide oxidation intermediates, which have sulfur-sulfur bonds, are known to be reactive toward free cyanide (Kelly et al 1969;Szekeres 1974;Luthy and Bruce 1979;Kamyshny 2009;Kamyshny et al 2009). Polysulfides, polythionates with four or more sulfur atoms, and soluble and colloidal elemental sulfur react with cyanide faster than trithionate and thiosulfate (Kelly et al 1969;Luthy and Bruce 1979;Kamyshny et al 2009).…”

“…Cyanide-reactive zero-valent sulfur in pore-waters was analyzed according to Kamyshny (2009). A sample was boiled with an excess of cyanide, and resulting thiocyanate was analyzed according to Rong et al (2005).…”