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 4°C in a dark bottle
Solid phenol is best liquified in a water bath at 60°C, 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.
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