The determination of nitrogen in woody tissue

A simple routine semi‐micro Kjeldahl procedure is described suitable for woody tissues. Some 250 mg. of milled tissue is digested with potassium sulphate, conc, sulphuric acid and mercuric oxide under a thermostatically controlled three‐stage electrical heating schedule, digestion being continued for 2 h. after clearing. Tests conducted with a variety of woody tissues give good reproducibility—coefficients of variation being all <3·5%, and N‐content values higher than by three other procedures based on combinations of selenium, copper sulphate and vanadium pentoxide. Recoveries from a range of N‐reference standards typical of compounds or structures present in plant materials show, with two exceptions, a high accuracy—within ·0·6%, and a high precision—coefficients of variation <0·6%. The poor recovery (85·3%) obtained with canavanine, which contains a N–O bond, is discussed and care is necessary before analysing tissues from families, e.g., the Leguminosae, liable to contain such linkages.