Nitrogen ammonia total kjeldahl

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]. 

The total nitrogen content is used to characterize numerous products and samples in the petrol, paper and carbon industries. These measurements can be carried out with CHN analysers as described previously, but to simplify the procedure, customized analysers have been developed for this single element. They are an alternative for cumbersome reference methods, such as total Kjeldahl nitrogen (TKN - corresponds to the sum of organic nitrogen and ammonia). 

TKN total Kjeldahl nitrogen NH3 — N ammonia nitrogen T — PO4 — P total phosphate phosphorous. 

Nelson and Sommers [44] have described a Kjeldahl digestion procedure for the determination of total nitrogen in soils in which the sample is digested with sulphuric acid using a selenium catalyst. The digest is steam distilled with sodium hydroxide and ammonia titrated with 3.5mM sulphuric acid. Various other workers have discussed the application of Kjeldahl digestion to the determination of total nitrogen in soils [45-47]. 

Total nitrogen estimations were performed on the polyamino acid solutions before hydrolysis by a semimicro-Kjeldahl technique. Amide-like nitrogen was measured on samples of the polyamino acids after hydrolysis in 2N HC1 for 2 hours under reflux by the Conway microdiffusion technique using No. 2 units. Ammonia was absorbed in 0.5% boric acid solution and titrated with 0.01 N HC1 using a micrometer syringe. 

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 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. 

A Kjeldahl analyzer is used to determine ammonia (by a digestionless method), or total organic nitrogen by acid digestion followed by steam distillation and potentiometric titration. This unit performs all steps automatically and calculates the %N in the sample. The technique is suitable for liquids and powders that can be catalytically converted to ammonium ion. This method is complementary to the combustion method, which is much faster and has become the method of choice for analysis of nitrogen content. 

The determination of total and organic nitrogen has been one of the most difficult tasks in marine chemistry. The oldest procedure is the Kjeldahl digestion, which is still in use on a microscale. The Kjeldahl method and a method by Krogh and Keys (1934) decompose and reduce the nitrogen components to ammonia which is then determined. 

The total nitrogen is found by Kjeldahl s method, in which a known weight of material is boiled with concentrated sulphuric acid until all its nitrogen has been fixed as ammonium sulphate. Excess of sodium hydroxide is then added to liberate the ammonia, which is distilled over into a known volume of standard acid. From the amount of acid neutralised, the volume of liberated ammonia can be calculated and expressed in terms of nitrogen. 

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