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Phenol hypochloride reagents

The detection of ammonium using phenol hypochloride reagents is also known as indophenol reaction or Berthelot reaction.


Phenol Nitroprusside reagent

Dissolve 7g phenol and 34 mg sodium nitroprusside [disodium pentacyanonitorsylferrate, Na2Fe(CN)5 NO 2 H2O] in 80 ml of water and make up to 100 ml. Store the reagent at 4C in a dark bottle
Solid phenol is best liquified in a water bath at 60C, and 7 g are pipetted into a 100 ml measuring cylinder standing on a balance (containing 80 ml water and the nitroprusside and a magnetic stirring bar). The cylinder is then moved to a magnetic stirrer and the volume is made up to 100 ml with water.

Hypochloride reagent

The buffered hypochloride reagent is prepared by dissolving 2.96 g NaOH in 140 ml of water, adding 29.74 g Na2HPO4 12 H2O and dissolving it completely. Then 16.6 ml of 12% NaOCl solution is added. The pH is brought to 11.4-12.2 (we usually adjust to 12.0) with NaOH and the volume is adjusted to 200 ml with water. This reagent is stored in a dark bottle at room temperature.

This protocol was taken from:
Keeney, D. and Nelson, D. (1982) In: Methods of Soil Analysis (Page, A., Miller, R., and Keeney, D. , eds.), Vol. 2 pp 674-675, Am. Soc. Agron., Soil Sci. Soc. America, Madison, WI.
Claus-Peter Witte, 2001