612 Analyst, September, 1974, Vol. 99, 9. 612 The Use of Filter-papers in the Determination of Nitrogen in Foods By D. PEARSON (National College of Food Technology, University of Reading, St. George’s A v e n w , Weybvidge, Surrey) Ix their paper, 0 hAlmhain and 6 Danachairl imply that it is inadvisable to use filter-papers for weighing out samples preparatory to the determination of nitrogen in foods as recom- mended by Pearson.2 The inclusion of an amount of ammonia-nitrogen of the order of 300 pg in a filter-paper of 12-5 cm diameter would appear to increase the volume of 0.1 N (0.05 M) sulphuric acid required for the titration in the Kjeldahl procedure by approximately 0.17 ml. Assuming, therefore, that the method is applied to a 2-g sample, the presence of the filter-paper would cause an increase in the calculated percentage of nitrogen of approximately 0.012 per cent.This difference is unlikely to he of significance in the analysis of most foods. For instance, the over-all effect in the examination of meat products would be an indication that a further 0.3 per cent. of meat was present. Taking into account the procedures used in our laboratories, the effect on the results obtained by the incorporation of a filter-paper (not an ashless or hard grade) in the digestion flask is considerably less than is indicated above. Apart from the fact that smaller (9 cm) papers are used, a similar filter-paper is included in the blank determination. This practice is referred to in the conclusions of d hAlmhain and d Danachairl and was recommended by Pearson3 in another text-book that was designed mainly to meet the requirements of less experienced workers. By using filter-papers from the centre of the box, variations in the nitrogen content between different papers should be extremely small. In the author’s opinion, filter-papers are most useful for the efficient transfer of moist foods into the digestion flask, but if the amount of nitrogen being determined is extremely small the sample should be weighed out in a perforated glass cup. REFERENCES 1. 2. 3. 6 hAlmhain, L., and 6 Danachair, D. , Analyst, 1974, 99, 211. Pearson, D., “The Chemical Analysis of Foods,” Sixth Edition, Churchill, London, 1970, p. I). “Laboratory Techniques in Food Analysis,” Batterworths, London, 1973, p. 53. Received May 6th, 1974 Accepted June 4th, 1974 0 SAC and the author.