A colorimetric method for the determination of antazoline in pharmaceutical preparations with sodium nitrite has been developed. The method involves treatment of a cooled and acidified dilute aqueous solution of the sample with sodium nitrite. The yellow colour produced is stabilised by the addition of propan-2-ol or ethanol and the absorbance then measured at 410 nm.

Naphazoline, tolazoline, clemizole, diphenhydramine, chlorpheniramine, ephedrine, cetrimide, benzalkonium chloride and zinc salts, even if present in amounts ten times greater than that of antazoline, do not interfere.