Resolution of thiosulfate interference in cyanide determination
Morgan, R.L.; Isom, G.E.; Way, J.L.
Toxicology and Applied Pharmacology 50(2): 323-328
1979
ISSN/ISBN: 0041-008X PMID: 41341 Document Number: 148261
Na2S2O3 is commonly employed as an antidote for CN- intoxication. Thiosulfate decomposes to SO2 which ultimately interferes with the colorimetric microdiffusion analysis of CN-. It is no longer reliable to determine CN- blood concentrations after therapy when Na2S2O3 has been instituted. A procedure was developed to prevent Na2S2O3 from interfering with the standard colorimetric method for CN- determination. Although thiosulfate is still degraded to polythionic acids, this procedure takes advantage of the difference in pKa values of HCN and the various acidic polythionic acids formed upon the acidification of the thiosulfate anion. To ascertain if this modification would circumvent thiosulfate interference under in vivo conditions, mice receiving KCN were subsequently treated with Na2S2O3 and the apparent concentration of CN- in the blood was determined. These studies indicate that the interference of CN- analysis caused by the presence of thiosulfate anion in biological samples can be resolved.