Simultaneous colorimetric determination of thiosulphate and thiocyanate in the culture medium of Rhizopus oryzae
1990
Ray, R.C. | Balagopalan, C. | Padmaja, G.
Thiosulphate and thiocyanate are two intermediate forms of S produced during oxidation of elemental S to sulphate in the culture medium of Rhizopus oryzae but no simple and specific method is available for determination of microgram quantities of these S forms in culture filtrates. A simple, rapid and precise colorimetric method is described for the simultaneous determination of thiocyanate and thiosulphate. The method is based on the cyanolytic reduction of thiosulphate in presence of Cu2+ to thiocyanate under alkaline conditions and determining the thiocyanate formed and/or present in the medium by reacting with ferric nitrate under acidic (HNO3) conditions which gives a reddish-brown colour. The colour intensity is measured spectrophotometrically at 460 nm. The method is rapid, sensitive and accurate and it permits determination of microgram quantities of thiocyanate or thiosulphate or both. The method was applied for the determination of thiosulphate and thiocyanate in the culture medium of R. oryzae amended with elemental S. Accumulation of thiosulphate and thiocyanate progressed for up to 6 days of incubation and thereafter declined, possibly due to conversion into sulphate and/or utilization in cell metabolism.
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