What is the correct way to preserve a sample for the phenol test?

Document ID

Document ID TE1773

Published Date

Published Date 27/05/2017
Question
What is the correct way to preserve a sample for the phenol test?
Summary
Phenol method sample preservation step
Answer
The phenol method has a preservation procedure to address sulfide interference and not the bacterial decomposition of the phenols, hence the 24 hour holding time. If the sample is preserved according to this method, a distillation is required or a precipitate will form upon addition of the Phenol 2 reagent. (This is not specified in the method.)

If the sample must be preserved and a distillation not performed phosphoric acid can be added to lower the pH and sodium hydroxide to return the pH of the sample.

Standard methods indicate storage using sulfuric acid which adjusts the pH to below 2 to prevent any microbial degradation of the phenols present and allows for a 28 day holding time. This procedure is adequate unless a sample has high sulfide levels, then use the phosphoric acid method with copper sulfate (perform distillation).