Determination of nitrogen in agricultural materials by the nessler reagent. II.—Micro-determinations in Plant Tissue and in Soil Extracts

✍ Scribed by S. H. Yuen; A. G. Pollard

• Publisher: John Wiley and Sons
• Year: 1954
• Tongue: English
• Weight: 515 KB
• Volume: 5
• Category: Article
• ISSN: 0022-5142
• DOI: 10.1002/jsfa.2740050803

✦ Synopsis

Abstract

The total nitrogen content of plant tissue may be determined by direct nesslerization of sulphuric acid‐hydrogen peroxide digests with accuracy up to 5%. Similar application to soil extracts involves somewhat greater errors.

In a spectrophotometric study of the Nessler colour, a filter showing maximum transmission at 420 mμ absorbs the greatest proportion of the colour.

In the sulphuric acid‐hydrogen peroxide digestion of plant tissue, added ammonia is fully recovered but added nitrate suffers a loss of 24‐47%, the percentage loss decreasing as the amount of nitrate present increases.

Bromothymol blue is a suitable internal indicator for the neutralization of test solutions before nesslerization. The blue colour of the indicator does not affect the absorptiometric measurement of the Nessler colour.

Soil solutions and soil extracts may be decolorized satisfactorily by a specially treated activated charcoal. This charcoal does not absorb appreciable amounts of ammonia from soil extracts made with Morgan's reagent, 2.5% acetic acid or water. For more accurate determinations of ammonia in soil extracts etc., distillation of the ammonia into acid in the presence of bromothymol blue, followed by nesslerization, is preferable.