A phenol‐hypochlorite manual determination of ammonium‐nitrogen in Kjeldahl digests of plant tissue

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Abstract
A phenol‐hypochlorite (Berthelot) procedure for determining NH4‐N in acid digests of plant tissue is described. EDTA suppresses Cu interference and precipitation of hydroxides and phosphates. The oxidizing reagent includes an alkaline buffer to account for variations in acidity between digestion solutions, the main source of error in an unbuffered procedure. The reagent combinations and addition sequence employed allow for delays of up to at least 30 minutes between reagent additions without affecting the final colour intensity. The proposed procedure is as sensitive as similar methods used for determining NH4‐N in natural waters and yields results which agree well with those obtained by steam distillation.