Nitrite titration according to USP general chapter <451>

Sulfonamides are drugs used to treat allergies and cough. They also have some antifungal and antimalarial activities.
USP<451> describes nitrite titration method for the determination of numerous pharmacopeial sulfonamide drugs and their dosage forms as well as of other pharmacopeial drugs with, for example, hydrazide (e.g., in isoniazid) and amine ester groups (e.g., in procaine) or amide derivatives of amino acids.

Here, for illustrating the analysis of the latter, the assay of the diagnostic agent aminohippuric acid is described.