Why does the TNT880 s-TKN report NO3 + NO2 while the TNT835 and TNT836 nitrate report only as NO3?
Difference between TNT880 and TNT835 and TNT836 results
The Method 10242 for Simplified TKN (s-TKN™) TNTplus Vial Test (0-16 mg/L N; Catalog Number/Order Code TNT880) is written for acid preserved samples and the Method 10206 Nitrate TNTplus Vial Test, LR (0.2-13.5 mg/L NO 3 -N) and HR (5-35 mg/L NO 3- -N; Catalog Number/Order Code TNT835 and TNT836) is not. Per the United States Environmental Protection Agency, testing for nitrate and nitrite separately does not allow acid preservation, but then the samples are acid preserved, the results are a sum of nitrate plus nitrite. The oxidation of nitrite to nitrate can occur under acidic conditions, and therefore the result with acid preservation cannot be conclusively determined to be due to nitrate only.