Micro-chemical test for nitrate

Author: Christine Bläuer

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back to Micro-chemical testing

More information about the necessary equipment and materials see Article Micro-chemistry.

Procedure

Evaporate the test drop to complete dryness. Place 1 or 2 crystals of diphenylamine[1] on the residue and add 1 drop of concentrated sulfuric acid. If NO3- is present the solution instantly turn blue to dark violet.

Substances that may inhibit the test or affect its delicacy:

The reaction is very sensitive but not very specific, as e.g. nitrites and other oxidizing reagents like chlorates or organic contaminants can produce the same color reaction. In our context, and especially when the micro-chemical test has for an aim to confirm the nature of microscopically determined salt phases.

Important notice on waste disposal

Diphenylamine is a poison. The test drops have to be collected in a separate waste container and disposed off accordingly (not in the canalization!). For each of these tests only one or two milliliters of waste water are produced, that can be collected and periodically disposed off. It should be no problem to find a bigger laboratory that will accept such small amounts of waste and handle them accordingly.

Literature

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