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Spectrophotometric Methods of Analysis1,2 The ultraviolet-visible spectrophotometry method is important in pharmaceutical analysis. It involves the measurement of the amount of ultraviolet (190–380 mm) or visible (380–800 mm) radiation absorbed by a substance in solution. Instruments that measure the ratio or a function of the ratio, of the intensity of two beams of light in the UV-visible region are called UV-visible spectrophotometers. Absorption of light in both the UV and visible regions of the electromagnetic spectrum occurs when the energy of the light matches that required to induce in the molecule an electronic transition and its associated vibrational and rotational transitions. It is thus convenient to consider the techniques of UV and visible spectrophotometry together. Derivative Method3 Derivative spectroscopy involves the conversion of a normal spectrum (fundamental, zero-order spectrum) to its first, second or higher derivative spectra by differentiating absorbance of the sample with respect to wavelength (λ). The differentiation of the zero-order spectrum can lead to separation of overlapped signals, elimination of background caused by presence of other compounds in a sample, improvement of resolution of mixtures as it enhances the detectability of mirror spectral features and enhancement of sensitivity and specificity. Derivative spectra yield a more characteristic profile in comparison to the parent one: new maxima and minima appeared and points, where derivative spectra cross the X-axis Derivative spectra, keeps all laws of classical spectrophotometry, e.g., dependence of derivative value on analyte concentration and additives law. These features allow the determination of several components in a mixture by measuring the amplitude of the derivative spectrum of mixture at several wavelengths. If the measured height of the derivative peak of analyte is performed at those wavelengths at which spectra of other components undergo zeroing, the measured amplitude is proportional only to the concentration of this analyte. This approach of quantitative determination is called the “zero-crossing technique.” This has been used for the simultaneous determination of different mixtures in pharmaceutical formulation.

international journal of pharmaceutical quality assurance

Analytical Method Development and Validation of First Order Derivative Spectrophotometric Method for Simultaneous Estimation of Telmisartan and Metformin Hydrochloride in their Combined Pharmaceutical Dosage Form