COMPARISON OF METHODS OF ANALYSIS OF CYANOGENS IN CASSAVA
For analysis of cyanide an electrochemical method using a cyanide electrode has been evaluated. The method gives reasonable results but is less sensitive and selective than the colorimetric methods based on the König reaction, and requires a blank determination for each analysis because of electrode interferences. Three colorimetric methods have been evaluated with regard to the dependence of the absorbance on the pH of the final colored solution. There is usually a small region of pH over which the absorbance is independent of pH, but some previous methods have worked in regions in which the absorbance is sensitive to small changes of pH. Acetate and phosphate buffers gave different absorbance behavior for the unstable pyridine/pyrazolone/bispyrazolone reagent and for the pyridine/barbituric acid reagent. Smelly and toxic pyridine was eliminated by use of isonicotinic acid/barbituric acid, which also gave an absorbance plateau at pH 5.5 – 6.5. A simple protocol is given, which will be useful in developing countries for analysis of cyanogens in cassava, using acid hydrolysis followed by isonicotinic acid/barbituric acid.