Abstract: Amidopyrine is oxidized to 4-aminoantipyrine, which is coupled oxidatively with phenol to form a red product; ammoniacal buffer medium of pH 7.5 to 8.5 and K3Fe(CN)6 as oxidant are used. The qualitative test is sensitive (~1 ppm), and no other common drug reacts in this way. Spectrophotometric measurement (at 510 nm) gives a rectilinear calibration graph for 0.04 to 0.4 mM amidopyrine. In the determination of amidopyrine in different medicaments, the coefficient of variation were <0.5%. Other methods of determination, viz, that involving oxidation by vanadate or titration of the base in acetic acid medium, give less reliable results. Up to 120 samples containing 10 to 100 ppm of 4-aminoantipyrine can be analyzed in 1 h by flow injection analysis based on the described reaction.

Abstract: Powdered tablets (20 mg) are ultrasonically dissolved in and diluted to 100 mL with water. The supernatant is analyzed with an L2-1000 flow injection analyzer. (flow diagram given) for determination of amidopyrine (I) by reaction with 1% FeCl3 to form a blue-violet compound. The absorbance of the solution is measured at 556 nm vs. a water blank. Calibration graph is rectilinear for 10 to 90 µg mL-1 of I. For 10 to 30 µg mL-1 of I, recoveries range from 99.9 to 102.7% with coefficient of variation of 1.1%.