Kjeldahl method, total nitrogen determination

Total nitrogen determinations in barley and malt gave slightly higher results by the Dumas than by the Kjeldahl method. The Dumas method was adopted as the reference method by the Analysis Committee of the Institute of Brewing27. Comparison of the results obtained by the Kjeldahl method with those of automatic N analyzers is mentioned in Section III.A.2 above. 

The Kjeldahl total nitrogen determination method is not very sensitive, hut it suits well for analyzing insoluble samples without preceding disintegration. Automated Kjeldahl protein estimations are used especially in food analysis. 

Calcium was determined by an EDTA method carbon and hydrogen by the combustion method total nitrogen by the Kjeldahl method sulfur by the Eschka method infrared spectra by the potassium bromide pellet technique. 

Commercially produced barium is analyzed for metallic impurities by means of emission spectroscopy. Carbon content can be determined by combustion, and nitrogen by the Kjeldahl method. Total barium can best be determined gravimetrically by precipitation as the sulfate. 

Useful check methods are (a) titration of the aspirin direct in dilute ethanol, or by the sodium citrate hydrolysis method given above b) a total nitrogen determination by the Kjeldahl method will check the figures found for phenacetin and caffeine. 

Total nitrogen is determined by chemical digestion (Kjeldahl-Gunning) methods. 

Carbon and hydrogen were determined by a microcombustion method and nitrogen by a micro-Kjeldahl method. The oxygen in the total samples was determined by neutron activation and that in the fractions by... 

Total nitrogen was determined in water using high-temperature oxidation and chemiluminescence,119 as well as microwave digestion-UV spectrophotometry.120 Total nitrogen in solid waste was determined by modified Kjeldahl-Nessler reagent colorimetrically and modified Kjeldahl titration with hydrochloric acid.121 No significant differences were found between the two methods in terms of accuracy and precision. 

The total nitrogen of the substrate was determined following the standard Kjeldahl method (8). The oil content of the cake was determined by gravimetry after extraction of the samples with n-hexane using a Soxhlet extraction apparatus (8). 

Analysis. The heating value, ash content, and sulfur distribution of the raw and treated coals were determined according to ASTM procedures (7). Iron in the extracts of the raw and treated coals was determined by titration with a cerium (IV) solution. Iron in the residues from the acid extractions of the raw and treated coals was determined spectrophotometrically using ferrozine (20). The liquid extracts were analyzed for total sulfur (as sulfate) by ion chromatography after separation of the sulfate from nitrate on an alumina column (21). Nitrogen was determined in the raw and treated coal and in their nitric acid-extracted residues by a modified Kjeldahl method. 

The commonly used methods for the determination of total nitrogen involve variations of the Dumas or Kjeldahl techniques. The Dumas approach involves oxidation of the nitrogen to elemental or oxide form by combustion of the sample, reduction of nitrogen oxides, and determination of the elemental nitrogen. The Dumas oxidation is usually represented by the following example for acetanilide ... 

The use of microwaves in the acceleration of digestion and colour development in the determination of total Kjeldahl nitrogen in soil has been examined [1]. Visual method based on the colour development of indothymol blue formed between ammonia and thymol has recently been developed for the determination of ammonia-nitrogen in environmental waters [2]. UV photo-oxidation of reduced forms of nitrogen to nitrate by peroxodisulfate can make a basis for the determination of total nitrogen in urban and industrial waste waters [3]. 

Another possibility is to take advantage of the individual treatment of every assayed sample. For sample lots with high variability in, e.g., pH or ionic strength, the required adjustments can be made in accordance with a prior assay performed in-line. This approach was proposed for the spectrophotometric determination of total nitrogen in Kjeldahl digests of plant leaves [397], As the method was very susceptible to sample acidity, which varied from sample to sample, individual sample pH adjustment was needed. To this end, an alkaline solution was added to every sample and the amount added was determined according to a pH-orientated feedback mechanism. This innovation was further applied to the spectrophotometric determination of aluminium in plant digests [398] and iron in estuarine waters [399], characterised by pronounced variations in... 

ISO 11261 1995 Soil quality - Determination of total nitrogen - Modified Kjeldahl method. 

Protein was determined by the method of Lowry (7) after hydrolysis with 0.2N NaOH (100°C, 15 min). Total nitrogen was measured by the micro-Kjeldahl method with sulfuric acid/hydrogen peroxide reagentj the ammonia was detected with Nessler s reagent. Glucose was measured by standard colorimetric assay using dinitrosalicylic acid. Starch was hydrolyzed with concentrated HC1 and then determined as sugar. 

In the early studies of ammonium fixation there was much uncertainty as to the amount of fixed ammonium present in untreated soils. The capacity of the soil for fixing ammonium could be determined readily by the methods already mentioned, but such techniques furnished no information on the amount of fixed ammonium present initially. Since surface soils usually fixed less ammonium than did subsoils, it seemed likely that this was because the surface soils already contained fixed ammonium, and also potassium. Determination of naturally-occurring fixed ammonium was difficult because it was not known if the Kjeldahl method for total nitrogen actually accounted for all of the fixed... 

In the classical Kjeldahl method, the proteins are digested (wet oxidized) in sulfuric acid with a catalyst (mercury and selenium tablets now succeed by the much safer potassium and copper sulfate tablets). An acid solution of ammonium sulfate is formed which is then diluted in water. The solution is made alkaline with sodium hydroxide and heated to distil off ammonia into excess standard acid sulfuric acid. The excess acid is back-titrated with standard sodium hydroxide to determine the amount of ammonia. It is more usual now to use boric acid in which to collect the ammonia and titrate with standard hydrochloric acid. The Kjeldahl procedure has been partially automated in systems such as the Kjeltec Analyzer. Total protein can be calculated as nitrogen content x 6.38. 

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