PMID: 9432866Feb 12, 1998Paper

Chromatographic determination of novamidazofen in pharmaceutical preparations

Acta pharmaceutica Hungarica
I Török, T Paál

Abstract

Novamidazofen (metamizol) has been used again as antipyretic and antirheumatic also in abroad recently. In aqueous solutions, such as injections, hydrolysis takes place in its formaldehyde sulfoxylate side chain resulting in an equilibrium mixture of novamidazofen and nor-amidazofen. A high-performance liquid chromatographic method was developed to study the hydrolysis and for the selective and accurate determination of the two components. UV detection at 242 nm wavelength, where the absorbance of novamidazofen and nor-amidazofen were identical, was applied. The rate constants k1 and k3 of the opposite direction reactions as well as K = k1 k3(-1), the hydrolytic equilibrium constant were determined. In aqueous solution, at I-->0 ionic strength and 25 degrees C pK = 3.52 +/- 0.12; 10(4) k1 = 1.74 (+/- 0.25) min-1, P = 0.95. Addition of methanol to the system decreased both the rate and equilibrium constants of the hydrolysis. For the quantitation of novamidazofen Nucleosil C18 column and 20 mmol dm-3 natrium sulphate in methanol-water 40 + 60 V + V eluent were used. The calibration curve was linear in the 20 to 1000 ng range. This method is suitable also for the detection of other, mostly oxidised impurities. A thin-layer chroma...Continue Reading

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