Is it necessary to acidify all samples when using TNT880 for Simplified TKN if the samples are not being preserved for later analysis?

Document ID

Document ID TE6963

Published Date

Published Date 25/01/2018
Question
Is it necessary to acidify all samples when using TNT880 for Simplified TKN if the samples are not being preserved for later analysis?
Summary
Acidifying samples for TNT880
Answer
It is necessary to acidify all samples when using Simplified TKN (s-TKN™) TNTplus Vial Test (0-16 mg/L N;  Catalog Number/Order Code TNT880), even if the samples are not being preserved for later analysis. TNT880 (Catalog Number/Order Code TNT880) calculates a TKN value by subtracting the Nitrate + Nitrite concentration in a sample from the Total Nitrogen concentration in the same sample. Acidifying the sample allows the oxidation of any Nitrite in the sample to Nitrate. The pH should be adjusted to less than 2 with concentrated sulfuric acid (approximately 2 mL per liter). When the samples are going to be run, they should be neutralized to a pH of 7 with 5 N sodium hydroxide. It is important to track the volumes of sulfuric acid and sodium hydroxide added so that the final test results can be corrected for the dilution caused by the volume additions.