Not more than 50 mg/kg
Dissolve 1 g of the sample in 90 ml of water, and slowly add 10 ml of a
freshly boiled and cooled solution of sodium hydroxide (1 in 10 soln). Allow
to settle, then decant 20 ml of the supernatant liquid into a colour
comparison tube, dilute to 50 ml with water, and add 2 ml of Nessler's TS.
Any colour does not exceed that produced by 10 µg of ammonium (NH4)
ion in 48 ml of water and 2 ml of the sodium hydroxide solution.