Spectrophotometric determination of some phenolic drugs in pure form and in their pharmaceutical preparations

Abstract EN

Two methods were described for the determination of etilefrine HCI (I), hexoprenaline HCI (II), levodopa (III) and carbidopa (IV) either in pure form or in pharmaceutical preparations.

Method (A) is based on oxidative coupling reaction between (I), (II) and (III) and 4-amino antipyrine ( 4-AAP) to produce coloured species.

The wavelengths for maximum absorption were 509, 494, and 530 nm for (I), (II) and (III), respectively.

Beer's law was obeyed in the concentration ranges 1-7, 5-50 and 2.5-20 ug/ml, while those obtained when applying Ringbom were found to be 1.5-4.3, 9.7-31.6 and 3.9-15.8 ug/ml for (I), (II) and (III), respectively.

The corresponding molar absorptivities were 1.78 x 104, 0.802 x 104 and 0.597 x 104 L.

mol-1.

cm-1 for (I), (II) and (III), respectively.

Method (B) depends on nitration of (I), (II) and (III) and (IV), using sodium cobalt nitrite in acetic acid medium.

The reaction products show maximum absorption at 360, 460, 320 and 360 nm for (I), (II), (III) and (IV), respectively.

Linear correlations were obtained between absorbance at the specific wavelength and concentrations in the range of 2-16, 8-64, 5-25 and 2.5-20 ug/ml, while Ringbom concentrations were found to be 2.51-12.58, 10-50.11, 5.623-22.38 and 3.16-15.84 ug/ml for (I), (II) and (III) and (IV), respectively.

The corresponding molar absorptivities were 1.248 x 104, 0.7303 x 104, 0.7327 x 104 and 1.052 x 104 L.

mol-1.cm-1 for (I), (II), (III) and (IV), respectively.

Results of analysis of pure drugs by the proposed methods were in good agreement with the official B.P.

and reference methods.

The proposed procedures were successfully applied to determine the studied drugs in their pharmaceutical dosage forms.