DETERMINATION OF N IN LIGNIN TOGETHER WITH NITRITE OR NITRATE

Various methods were used to determine N in lignin, both directly and in buffered aqueous solutions (pH 7.0 and 5.5) containing lignin and NO2\tor lignin and NO3·t. The percentage recovery of N was highly variable, being dependent on the analytical method and on pH. There appeared to be a reaction between lignin and NO2·tor NO3·tduring the analytical procedure. The Kjeldahl method achieved a higher recovery of organic N from pure lignin than the persulphate method, but it showed a higher coefficient of variation. In buffered samples containing lignin together with NO2·tor NO3·t, recoveries of NO2·tand NO3·twere considerably lower for the Montgomery and Dymock and the Devarda methods than for the procedure using an auto-analyzer. The former procedures appeared to fix NOx·t. With the auto-analyzer and the Devarda methods, recovery was increased with increasing pH values. The Kjeldahl method gave very high standard deviations. It proved unreliable for the analysis of organic N in samples containing both lignin and NOx·t. During the persulphate analysis, significant N losses were calculated, probably because of acid-induced nitrosation or nitration and subsequent volatilization of N during the persulphate analysis itself. © 1990 Springer-Verlag.