Comparison of HgO and CuSO4/TiO2 as catalysts in manual Kjeldahl digestion for determination of crude protein in animal feed: collaborative study.

Because of environmental concerns about HgO, and because of lengthy digestion requirements for HgO and CuSO4, interest in alternative catalysts for the Kjeldahl determination of animal feeds remains high. A digestion system using a mixed CuSO4/TiO2 catalyst has been found to reduce digestion times to 40 min. A collaborative study was carried out to compare this system to the official AOAC HgO method, 7.015. Thirty-eight samples, consisting of blind duplicates of closely matched pairs and 2 standard materials, were analyzed once by each method. Results were received from 13 laboratories. Means and standard deviations of individual samples were comparable, with an overall difference of grand means of 0.005% protein. With only one exception, analyses of variance showed no significant method difference at the 95% confidence level. The CuSO4/TiO2 method has been approved interim official first action as an alternative method for determination of crude protein in animal feed.