Does Sodium Thiosulfate need to be added to all samples tested using Ammonia methods?

Document ID

Document ID TE11176

Version

Version 1.0

Status

Status Published

Published Date

Published Date 04/16/2019
Question
Does Sodium Thiosulfate need to be added to all samples tested using Ammonia methods?
Summary
Clarification on statements made in the sample collection and storage sections of the method documents.
Answer
Many of the Salicylate methods for Ammonia including: 8155, 10023, and 10031 have a statement in the sample collection and storage section that says " If chlorine is known to be present, add one drop of 0.1 N Sodium Thiosulfate to 1 L of sample for each 0.3 mg/L Cl2"

However, Chlorine is not listed as an interference section in these methods. So dechlorination using Sodium Thiosulfate is not necessary if samples are tested immediately (within 15 minutes) after collection.

That statement in the sample collection and storage section is specifically for samples that are being collected for later analysis.

Although not specified on the method documentation for TNT830, TNT831, TNT832, and TNT833, this information also applies to these tests as they use the same chemistry.

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