A spectrophotometric method for the determination of biuret in urea-based fertilizers using Cu(OH)2(s) as analytical reagent is proposed. The principle of the method is the reaction between biuret and Cu(OH)2 (s) and formation of the purple complex Cu(C2N3O2H5)2 that presents absorption maximum at 510 nm. After establishment of analytical conditions, the method was applied to the determination of biuret in two commercial urea samples used as fertilizer and foodstuffs in agriculture. For analytical solutions prepared in the 0.1 - 0.5% (m/v) biuret, analytical curves with typical correlation coefficient of 0.9990 were always obtained. Results obtained by the proposed procedure were in agreement with those obtained by atomic absorption spectrometry at 95% confidence level. Accuracy was also evaluated by means of addition and recovery tests using spiked samples with biuret. Recoveries in the 92 - 100% were obtained and the calculated relative standard deviation of a sample containing 0.31% (m/v) biuret after twelve successive measurements was 2%.
biuret; fertilizer; spectrophotometry
