text: Phenol in the Berthelot reagent can be replaced by a variety of phenolic reagents, the most common being sodium salicylate, which is significantly less toxic. This has been used for blood urea nitrogen (BUN) determinations and commonly is used to determine water and soil total and ammonia-N.  Replacement of phenol by 2-phenylphenol reduces interferences by a variety of soil and water constituents and improves color stability at slightly lower pH.