[Determination of sulfonamides and local anaesthetics by coulometry (author's transl)]

Use of 7,7,8,8-tetracyanoquinodimethane for spectrophotometric determination of certain local anaesthetics and procainamide hydrochloride

A simple and rapid spectrophotometric procedure has been developed for the determination of four local anaesthetics containing a free primary amine moiety and of procainamide hydrochloride as the drug substances and in dosage forms. The method is based on the reaction of the drug with 7,7,8,8-tetracyanoquinodimethane in alkaline solution to produce yellow products. The chromogen was measured at 473 nm. The effects of several variables on colour development were established. Job's plots of absorbance versus molar ratio of drug to reagent indicated a 1:1 ratio for all the drugs studied. Results of the analysis of drug substances and their dosage forms by the proposed method are in good agreement with those obtained by the USP XX method.

Colorimetric assay of benzocaine and some dosage forms

A colorimetric procedure for benzocaine and a number of its dosage forms was developed; it offers improvement in ease, speed, and sensitivity over the official method. The method is based on the formation of a red Schiff base between benzocaine and p-dimethylaminocinnamaldehyde in a nonaqueous acidic medium. At the maximum absorption of 544 nm, the Beer-Lambert law was adhered to over the 0.025--2.5-microgram/ml range. Best accuracy can be obtained for solutions containing 0.25--1.25 microgram/ml. The color was stable for at least 2 hr. Analysis of benzocaine in the dosage forms studied can be directly performed without prior drug extraction.