Detection of nitrate and nitrite

Qualitative test for Nitrite
Nitrate is less toxic but when converted into nitrite in the rumen or in the forage/silage as an intermediary product before being converted into ammonia it is more toxic (6-10 times more than nitrate). A simple field test for detection of nitrite is cooking test.
Aim
To detect the presence of nitrite in the blood.
Procedure
1. Draw blood (10 ml) without anticoagulant from an affected and a known normal animal in 20 ml capacity test tubes.
2. Place them in boiling water bath for 45 minutes. Cool them.
3. Observe the colour of the blood and the surface.
Inference
Nitrite containing blood sample is salmon pink in colour does not pull away from the side and the surface is level or concave. Normal blood sample is chocolate brown, pulls away from the side of tube and the surface is convex.
Second test for Nitrite.
Materials and chemicals
Sulphanilic acid, glacial acetic acid, α-naphthyl amine hydrochloride.
Procedure
1. Dissolve 0.5 g of sulphanilic acid in 150 ml of 20% glacial acetic acid-solution A.
2. Dissolve 0.2 gof α-naphthylamine hydrochloride in 150 ml of 20% glacial acetic acid by gently heating - solution B.
3. In a small test tube the given sample is taken (solution of feed material or ruminal contents) and 2 ml of solution A and B are added. Observe the colour.
Inference
A pink to red colour is positive for the presence of nitrites.
v Nitrite is easily decomposed and destroyed hence it may not be present in the sample preserved for chemical analysis even in cases of definite nitrite poisoning.
Qualitative test for Nitrate in a plant sample
Materials and chemicals
Sulphuric acid, diphenylamine and glass slide.
Procedure
1. Dissolve 0.5 g of diphenylamine in 20 ml of distilled water and make the volume to 100 ml with sulphuric acid.
2. Store it in amber coloured bottle. This is full strength solution and can be made into half strength by diluting with equal parts of 80% sulphuric acid.
3. To test a plant place a drop of the test reagent on the cut surface of plant. Observe the colour.
Inference
o A green to blue colour indicates the presence of nitrate.
A green to blue colour with a half strength solution indicates + + for nitrate which could be toxic to animal.