Quantification of free and metal-complexed cyanide by tetrathionate derivatization

Abstract

A sensitive and robust method for detection of free and metal-complexed cyanide in solutions is described. The method does not require a distillation step and is applicable for both low ionic strength and sea-water samples. The method is based on the reaction of cyanide with potassium tetrathionate followed by highperformance liquid chromatography (HPLC) separation and UV detection of formed thiocyanate. The detection limit of the method is 250 nmol L À1 cyanide (6.5 mg L À1 CN À ) without a pre-concentration step. Storage for three days does not significantly change the results. The sum of free and weak metal-complexed cyanide can be measured by tetrathionate derivatization at a pH of 10. The sum of free, weak metal-complexed cyanide, iron(II) and iron(III)-complexed cyanides may be measured by tetrathionate derivatization at pH 4.4. Derivatization requires heating to 90 C for 20 min at pH ¼ 10 and for 12 h at pH ¼ 4.4. Weighted mean recoveries for free, iron(II), iron(III), nickel(II), silver(I), Cd(II) and Zn(II) complexed cyanide were in the range of 87 to 112% and weighted standard deviations were in the range of 1.7 to 10.0%. The method is not applicable for cyanide complexes of gold and cobalt. We illustrate an application of cyanide quantification using pore-waters from the Delaware Great Marsh.

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

“…It should be mentioned that although the limit of cyanide detection is 0.25 lmol L -1 , its concentration is calculated as a difference between thiocyanate concentrations after and before tetrathionate derivatization, and therefore, reported concentrations of cyanide sometimes are below 0.25 lmol L -1 , or even negative. Standard deviation of analysis of concentrations of free and complexed cyanide is 10 % (Kamyshny et al 2012).…”

“…Tetrathionate has been shown to be reactive toward iron-complexed cyanide as well at pH = 4.4 and elevated temperatures (Kamyshny et al 2012).…”

“…The sample was centrifuged, and the supernatant was analyzed for thiocyanate concentration according to Rong et al (2005). For thiocyanate determination, 10 mL of pH = 4.4 (Kamyshny et al 2012) buffer was added to 1.6-4.6 g of sediment and the sample was shaken overnight. Thiocyanate concentration in supernatant was detected after centrifugation according to Rong et al (2005).…”

“…For cyanide determination, 0.5-1.5 g of sediment was mixed with 9 mL Milli-Q water, 1 mL pH = 4.4 buffer (Kamyshny et al 2012) and 0.2 mL 500 mmol L -1 of potassium tetrathionate solution, shaken for 15 min and heated overnight at 90°C. The sample was centrifuged, and the supernatant was analyzed for thiocyanate concentration according to Rong et al (2005).…”

“…Pore-water cyanide concentrations were measured according to Kamyshny et al (2012) by derivatization with potassium tetrathionate. Reactions between cyanide and zero-valent sulfur species have been used for decades as the basis for analytical techniques for detection of the latter.…”