Nitrite $\left({\mathrm{NO}}_2^{-}\right)$ interferes in the 'ring test' of nitrate $\left({\mathrm{NO}}_3^{-}\right)$. Some of the following reagents can be used for the removal of nitrate.

(P) Potassium dichromate(s) 

(Q) $\mathrm{CO}{\left({\mathrm{NH}}_2\right)}_2$ (urea) 

(R) ${\mathrm{NH}}_2{\mathrm{SO}}_3\mathrm{H}$ (sulphamic acid)

(S) Zinc/ sodium hydroxide

A nitrogen-containing chemical substance that can be discovered in bodily fluids like urine. Carbon dioxide and ammonia are combined to create urea. Urea can be a source of nitrogen for ruminants or used as fertilizer.
Industrial processes use urea with a combination of sulfur trioxide and sulfuric acid to make sulfamic acid (or oleum).

$$\begin{gathered} {\mathrm{NH}}_2\stackrel{\underset{\parallel }{\mathrm{O}}}{\mathrm{C}}-{\mathrm{NH}}_2+{\mathrm{NO}}_2^{-}+{\mathrm{H}}^{+}⟶{\mathrm{N}}_2\uparrow +{\mathrm{CO}}_2\uparrow +{\mathrm{H}}_2\mathrm{O} \\ {\mathrm{H}}_2\mathrm{N}-\stackrel{\underset{\parallel }{\mathrm{S}}}{\mathrm{C}}-{\mathrm{NH}}_2+{\mathrm{HNO}}_2\to {\mathrm{N}}_2\uparrow +{\mathrm{H}}^{+}+{\mathrm{SCN}}^{-}+{\mathrm{H}}_2\mathrm{O} \\ \mathrm{HO}\cdot {\mathrm{SO}}_2\cdot {\mathrm{NH}}_2+{\mathrm{HNO}}_2⟶{\mathrm{N}}_2\uparrow +2{\mathrm{H}}^{+}+{\mathrm{SO}}_4^{2-}+{\mathrm{H}}_2\mathrm{O} \end{gathered}$$