Use of inverse multiple linear regression (ILS) for the analytical control of pharmaceutical preparations. UV-visible spectrophotometric quantitation of an active principal in the presence of absorbing excipients

The simplicity and robustness of inverse multiple linear regression (ILS) as a method for the analytical control of pharmaceutical preparations by UV-vis spectrophotometry is demonstrated. This calibration technique establishes a linear relation between the analyte concentration as dependent variable and absorbance values measured at a small number of wavelengths as independent variables. In this work, ILS was used to quantify the active principal in a pharmaceutical preparation commercially available as aqueous solution. The preparation was diluted in 40:60 v/v methanol/aqueous 0.1 N NaOH and its UV spectrum recorded over the wavelength range 240-330 nm. The calibration equation was derived from laboratory-made solutions of the analyte and absorbing excipients in the preparation. The operating wavelengths used were those of the absorption maxima for the compounds of interest; the results are compared with those obtained by stepwise wavelength selection and high performance liquid chromatography (HPLC).