Which acid should be used to preserve nitrogen ammonia samples using TNT+ reagents?

Document ID

Document ID TE140

Published Date

Published Date 27/05/2017
Question
Which acid should be used to preserve nitrogen ammonia samples using TNT+ reagents?
Summary
Recommended acid preservation for nitrogen-ammonia TNTplus reagent sets
Answer
Provided below are the calculations to demonstrate the use of hydrochloric acid (HCl) versus sulfuric acid (H2SO4) to acid preserve nitrogen-ammonia TNTplus reagent sets.

Chloride and sulfate both interfere at approximately 1000 ppm using the TNTplus methods for nitrogen-ammonia. Use hydrochloric acid (HCl) instead of sulfuric acid (H2SO4) because ACS grade hydrochloric has a lower concentration than ACS grade sulfuric acid, and chloride has a lower ionic mass.

2 ml HCl (12 moles chloride/1000 ml)(35.45 g chloride/1 mole chloride) = 0.851 g chloride per liter sample = 850 mg/L chloride
2 ml H2SO4 (18 moles sulfate/1000 ml)(96.1 g sulfate/1 mole sulfate) = 3.46 g sulfate per liter sample = 3,460 mg/L sulfate

Based on these calculations, avoid sulfuric acid to preserve nitrogen-ammonia samples using TNTplus reagent sets. If HCl preservation is required for reporting purposes, no more than 2 ml of ACS grade hydrochloric acid is recommended.