The Determination of Micro Amounts of Polythionates. III. A Photometric Method for the Determination of Tetrathionate by Means of Its Cyanolysis

Abstract

Abstract A photometric method capable of determining tetrathionate by exactly the same procedure as that used for pentathionate and hexathionate has been established. The optimum pH ranges for the reactions of tetrathionate, pentathionate and hexathionate with cyanide are 8.3–12.1, 8.0–8.8, and 7.8–8.9 respectively for the recommended procedure. From a consideration of the above experimental facts, it has been concluded that tetrathionate can be determined accurately by exactly the same procedure as that used for pentathionate and hexathionate when the pH value is within the range from 8.3 to 8.8. To the standard tetrathionate solution first the buffer solution and then a solution of sodium cyanide are added in order that the pH value of the mixture solution after the addition of the cyanide solution may be within the 8.3–8.8 range. The mixed solution is kept in the thermostat at 40°C for 30 min.; the tetrathionate is thereby converted into thiocyanate quantitatively. After the addition of a ferric nitrate - perchloric acid solution, the absorbancy of the solution of ferric-thiocyanate complex formed is measured at the wavelength of 460 mμ.