Kjeldahl method . fluids with reference to the nitrogen analysis of biological Assessment of automated

The established Kjeldahl technique for estimating nitrogen (King and Wooton, 1956) was employed using a Markham still and standardized sulphuric acid and sodium hydroxide with phenolpthalein as indicator. Urinary nitrogen was estimated on 1 ml aliquots. For faeces and food 10-20 g aliquots of homogenate previously prepared with a Silverson mixer were weighed and digested on the macro scale. The digests were then diluted to 100 ml and 10 ml aliquots used for distillation. All estimations were carried out at least in duplicate. The AutoAnalyzer method used was that of Marten (1964) (flow diagram Fig. 1) with a digestion mixture consisting of 90% sulphuric acid, 2% perchloric acid, 05% mercuric sulphate, and 0-02% selenium dioxide. The digestion current was set at 4 amps and 7 amps and the sampling rate 60/hr with a water wash between each sample. These conditions were adhered to for all materials. A suggestion that foodstuffs would require more catalyst and a higher temperature proved invalid; increasing the perchloric acid concentration to 10% did not affect the results and the equipment fused whenever the current was raised to 5 amps and 8 amps. All assays incorporated two series of standards using dilutions of nicotinamide and of a urine of known nitrogen content, determined earlier by replicate manual Kjeldahl estimations. These standards curves were found to coincide for nitrogen values up to approximately 1,200,ug.N/ml. Assays were performed in duplicate on urine and in quadruplicate on faeces and diets. Estimations were carried out on pools of urine and of faeces and on samples of patients' daily diets. Faeces and diets were obtained as homogenates. Because a Solid Prep. Sampler was not available sampling of these homogenates and blockage of the manifold proved a persistent problem, so all nipples and fine sampling tubing were eliminated from the introduction manifold