It is generally unnecessary to test the purity of purchased nitrite
You will need for testing:
• 5gm of sodium nitrite • Digital scales • 2ml disposable pipette, • 2 x one litre bottles of distilled water
Accurately weigh out 5gm of the salt that is to be tested. Then, from a one litre bottle of distilled water, pour out 10 - 20 ml into a separate container. Stir the salt in this distilled water for a few minutes until dissolved. Once the salt is dissolved in the sample of distilled water, return the mixture to the one litre bottle, re-seal the bottle, shake and then re-open.
The next step is to withdraw exactly 2 ml of the water and add it to the second 1liter bottle of distilled water. Seal and shake the bottle. When well shaken, open and immerse a nitrite dipstick into the liquid. Wait 30 seconds and then read from the colour chart the concentration of nitrite in the second water bottle. If the original 5gm sample is pure, the expected colour change that matches 10 mg/ litre will be seen. If lower concentrations are noticed it is likely the original sample of nitrite is not 100% pure.
Bartovation Nitrite test strips are available at: https://www.amazon.com/Nitrite-Nitrate-0-500-Strip-Strips/dp/B07WTXM6DB