Determination of biuret in urea and mixed fertilizers

A new method has been developed for the determination of biuret in urea, based on the separation of the copper-biuret complex with the aid of an anionexchanger, followed by titration of the bound copper with EDTA. This method may be used directly for the determination of biuret in solutions and in end-products of a urea factory, even with biuret contents down to 0.001%. The well-known photometric method cannot be used for less than 0.1% biuret contents; corrections are needed for the interference of urea, and ammonia and insoluble products have to be removed. Both methods are suitable for the determination of biuret in mixed fertilizers down to 0.5%, provided that cations are first removed on a cation exchanger. However, the photometric determination calls for special precautions with regard to acidity when phosphates are present.