Automated flow injection spectrophotometric non-aqueous pseudotitrations of amines and their hydrohalide salts

Abstract

An automated flow injection pseudotitrimetric determination of amines and their hydrochloride salts is described. The method is based on the injection of 200 µl of acetous sample solution into a flowing stream of acetous perchloric acid-malachite green “titrant” and measuring the peak width of the transmittance transitions at 621 nm, the λ_max. of the basic form of the indicator. Equivalence times of 10–40 s were measured with an RSD of less than 1 %(n= 5) and the analytical range was 1–20 × 10^–3M in most instances. The measurement rate is high (60–100 h^–1), with a consumption of only 3–6 ml of the acetous titrant per run. The method can be used for the determination of the purity of crude drugs and for the assay of pharmaceutical formulations in the absence of basic excipients. Examples are given for theophylline, caffeine, and chlorpromazine, thiamine and procarbazine hydrochlorides.