Spectrophotometric determination of isopropylantipyrine in pharmaceutical preparations

Studies on analysis of mixed pharmaceutical preparations. VIII

Abstract

Isopropylantipyrine (I) reacts with Fe (NO₃) ₃ in acidic medium to give a red violet color with maximum absorption at 510 mμ.
A new spectrophotometric method, based on this color reaction, has been established to the determination of (I) in pharmaceutical preparations.
Influences of 47 compounds on the determination were examined. The interferences from sulpyrine, aminopyrine, aminopropyrone, antipyrine, salicylate, ribofravine phosphate, codeine phosphate, etc. are eliminated by the chloroform extraction, either in an acidic or an alkaline medium.
The procedure recommended is as follows. A sample {containing 50 mg of (I)} is taken into a separatory funnel. To this is added 10 ml of water and 10 ml of 10% H₂SO₄ solution, and it is extracted 6 times with 30 ml portions of chloroform. The combined extract is evaporated on a water bath, and the residue is dissolved in 10 ml of ethanol. It is then diluted with water exactly to 100 ml.
A 10 ml aliquot is transfered to a 25 ml volumetric flask. Ten milliliter of 20% Fe (NO₃) ₃ solution is added, and it is diluted to 25 ml with water.
The absorbance is measured at 510 mμ (E_T) against blank. At the same time, the absorbance of standard solution (E_S) is determined, and the amount of (I) is calculated by E_T/E_S.