Micro-chemical test for nitrate

Author: Christine Bläuer

back to Micro-chemical testing

Fpr more information on the required equipment and materials see the Micro-chemistry article.

Procedure

Evaporate the sample 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 turns blue to dark violet or purple.

Substances that may inhibit the test or affect its sensitivity:

The reaction is very sensitive but not very specific, as other oxidizing reagents can produce the same color. In our context the test is usually adequate, especially when the micro-chemical test has the aim of confirming the nature of microscopically determined salt phases present.

Important notice on waste disposal

Diphenylamine is poisonous. The test drops have to be collected in a separate waste container and disposed of accordingly (not down the drain!). 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 appropriately.