Selenium as Catalyst in Kjeldahl Digestions

Patel, S. M.; Sreenivasan, A.

doi:10.1021/ac60013a015

Cited by 32 publications

(11 citation statements)

References 31 publications

(24 reference statements)

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“…These conclusions are supported by Tables 10-12, which show that no nitrogen was lost when small amounts of selenium were used for Kjeldahl digestions involving the customary amounts of potassium sulphate even when digestion was prolonged, whereas there were losses when the quantity of selenium or the concentration of potassium sulphate was increased, particularly with long periods of digestion. Reports by Patel & Sreenivasan (1948) and Anantakrishnan & Srinivasa Pai (1952) that serious loss of nitrogen occurs even when small amounts of selenium are used with low concentrations of potassium sulphate could not be confirmed (Table 12; cf. results by standard method in Table 2 and by Piper's method in Table 6).…”

Section: Loss Of Sulphuric Acid During Kjeldahl Digestionmentioning

confidence: 94%

Determination of nitrogen in soil by the Kjeldahl method

1960

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1. The reliability of the Kjeldahl method for the determination of nitrogen in soils has been investigated using a range of soils containing from 0·03 to 2·7% nitrogen.2. The same result was obtained when soil was analysed by a variety of Kjeldahl procedures which included methods known to recover various forms of nitrogen not determined by Kjeldahl procedures commonly employed for soil analysis. From this and other evidence presented it is concluded that very little, if any, of the nitrogen in the soils examined was in the form of highly refractory nitrogen compounds or of compounds containing N—N or N—O linkages.3. Results by the method of determining nitrogen in soils recommended by the Association of Official Agricultural Chemists were 10–37% lower than those obtained by other methods tested. Satisfactory results were obtained by this method when the period of digestion recommended was increased.4. Ammonium-N fixed by clay minerals is determined by the Kjeldahl method.5. Selenium and mercury are considerably more effective than copper for catalysis of Kjeldahl digestion of soil. Conditions leading to loss of nitrogen using selenium are defined, and difficulties encountered using mercury are discussed.6. The most important factor in Kjeldahl analysis is the temperature of digestion with sulphuric acid, which is controlled largely by the amount of potassium (or sodium) sulphate used for digestion.7. The period of digestion required for Kjeldahl analysis of soil depends on the concentration of potassium sulphate in the digest. When the concentration is low (e.g. 0·3 g./ml. sulphuric acid) it is necessary to digest for several hours; when it is high (e.g. 1·0 g./ml. sulphuric acid) short periods of digestion are adequate. Catalysts greatly affect the rate of digestion when the salt concentration is low, but have little effect when the salt concentration is high.8. Nitrogen is lost during Kjeldahl analysis when the temperature of digestion exceeds about 400° C.9. Determinations of the amounts of sulphuric acid consumed by various mineral and organic soils during Kjeldahl digestion showed that there is little risk of loss of nitrogen under the conditions usually employed for Kjeldahl digestion of soil. Acid consumption values for various soil constituents are given, from which the amounts of sulphuric acid likely to be consumed during Kjeldahl digestion of different types of soil can be calculated.10. Semi-micro Kjeldahl methods of determining soil nitrogen gave the same results as macro-Kjeldahl methods.11. The use of the Hoskins apparatus for the determination of ammonium is described.12. It is concluded that the Kjeldahl method is satisfactory for the determination of nitrogen in soils provided a few simple precautions are observed. The merits and defects of different Kjeldahl procedures are discussed.

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Section: Loss Of Sulphuric Acid During Kjeldahl Digestionmentioning

confidence: 94%

Determination of nitrogen in soil by the Kjeldahl method

1960

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“…With regard to the catalyst, survey of the literature indicates that mercury is the only 'safe' catalyst, with which no losses have been reported (Bradstreet, 1965;Fleck & Munro, 196 j). Reports of losses with selenium or copper or mixtures of these date back to the 1930's (see Fleck & Munro, 1965) with adequate confirmation in 1948 (Hiller, Plazin & Van Slyke, 1948;Patel & Sreenivasan, 1948). T h e disadvantage of mercury is that it forms a mercury-ammonium complex which must be decomposed before determining ammonia.…”

Section: Kjeldahl Methodsmentioning

confidence: 99%

“…Reports of losses with selenium or copper or mixtures of these date back to the 1930's (see Fleck & Munro, 1965) with adequate confirmation in 1948 (Hiller, Plazin & Van Slyke, 1948;Patel & Sreenivasan, 1948). T h e disadvantage of mercury is that it forms a mercury-ammonium complex which must be decomposed before determining ammonia.…”

mentioning

confidence: 99%

Total nitrogen determination

Morgan

1970

Proc. Nutr. Soc.

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“…The 1-hour afterboil is much less than that recommended by Shirley and Becker ( 12) and others (6, 7). Patel and Sreenivasan (8) found that if the afterboil were extended to 6 hours considerable nitrogen was lost. They found a mercuric oxide-selenium mixture to be a more effective catalyst than either alone when used on refractory nitrogen compounds.…”

Section: Literature Citedmentioning

confidence: 99%

Hydrazones, Semicarbazones, and Other Nitrogenous Substances Reqiring Reductive Pretreatment

Fish¹

1952

Anal. Chem.

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Selenium as Catalyst in Kjeldahl Digestions

Cited by 32 publications

References 31 publications

Determination of nitrogen in soil by the Kjeldahl method

Determination of nitrogen in soil by the Kjeldahl method

Total nitrogen determination

Hydrazones, Semicarbazones, and Other Nitrogenous Substances Reqiring Reductive Pretreatment

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