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

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%.