Determination of Nitrogen in Pyridine Ring-Type Compounds by Kjeldahl Method

Abstract

THIS laboratory nitrogen must be determined by the Kjeldahl method on many types of research samples. The necessary modifications of methods for determining nitro, nitrate, azo, and other nitrogen groups are well known and reasonably

Kjeldahl Method for Organic Nitrogen

“…Fish (18) reduced hydrazones, semicarbazones, and similar compounds by use of zinc dust and methanol in hydrochloric acid. It has been claimed (63) that by the use of mercury or mercury-selenium oxychloride catalysts, and prolonged digestion, refractory compounds such as pyridine, quinoline, and nicotinic acid can be determined. This procedure has been adapted to micro and semimicrodeterminations (45).…”

The Cystine Plus Cysteine and Methionine Contents of the Seed Proteins, and Sulphur Distributions of Seeds of Vicia Spp. (Vetches), With Notes on Their Cyanogenesis

“…Kaye and Weiner (1945) showed that with HgO alone complete recovery of N was attained in resistant N ring compounds such as pyridine, pyrimidine, thiazole, pyrrole, quinoline and others, and White and Secor (1946) similarly showed for tryptophane and gramirddin that 60-90 minute digestion with a 5:1 ratio of HgO to compound was sufficient. Shirley and Becker (1945) found that Hg + SeOClo catalyst completely converts N in nicotine, caffeine, pyridine, and quinoline into ammonia N in three hours after "clearing'' (see also Clark, 1941). It is probable, therefore, that the combination of mercury-selenium will be more efficient as a catalyst for biological material such as seeds, than either HgO or SeO2 alone.…”

Selenium as Catalyst in Kjeldahl Digestions

“…is obtained when a combination of selenium and mercuric oxide is,used as catalyst; this is due to the THE catalytic effect of small amounts of selenium, selenium oxychloride, selinites, or selenates in the oxidative digestion of nitrogenous organic matter by the Kjeldahl method is well known (5,13,17,20,28,32). A combination of mercuric oxide and selenium acts much more effectively than either of them singly in accelerating the decomposition of proteins (1,4, #3, 25, S3, So).…”

“…On the other hand, provided an adequate period of afterboil following clearance of the digest is given, correct results are obtained (2, 6, 10, 26) and the erratic results sometimes obtained with selenium compounds may frequently be due to insufficient digestion (3,25,28). Clark (11) was of the opinion that many compounds, although requiring a very long digestion period, will nevertheless yield their nitrogen quantitatively to one or the other of the modified Kjeldahl procedures.…”

“…Several cyclic nitrogen compounds are extremely resistant to oxidation by the Kjeldahl method (8, 19, 34). However, several workers (7,11,28) were able to analyze this type of compound apparently successfully by using mercuric oxide alone or a mixture of mercuric oxide and selenium as catalysts. In Table III are given the results obtained with two typically refractory compounds, nicotinic acid and quinoline, digested for varying periods of time using ordinary salt mixture as such, with selenium 'and with selenium and mercuric oxide as catalysts.…”