Novel ratio difference at coabsorptive point spectrophotometric method for determination of components with wide variation in their absorptivities

• Novel ratio difference at coabsorptive point.
• Coabsorptive point as an extension to isoabsorptive point and absorption factor.
• A coabsorptive point in the absorption spectra will be retained in ratio spectra.
• Single step analysis of compounds exhibiting wide variation in their absorptivities.
• No reported spectrophotometric method for perindopril arginine–amlodipine mixture.

Different methods have been introduced to enhance selectivity of UV-spectrophotometry thus enabling accurate determination of co-formulated components, however mixtures whose components exhibit wide variation in absorptivities has been an obstacle against application of UV-spectrophotometry. The developed ratio difference at coabsorptive point method (RDC) represents a simple effective solution for the mentioned problem, where the additive property of light absorbance enabled the consideration of the two components as multiples of the lower absorptivity component at certain wavelength (coabsorptive point), at which their total concentration multiples could be determined, whereas the other component was selectively determined by applying the ratio difference method in a single step. Mixture of perindopril arginine (PA) and amlodipine besylate (AM) figures that problem, where the low absorptivity of PA relative to AM hinders selective spectrophotometric determination of PA. The developed method successfully determined both components in the overlapped region of their spectra with accuracy 99.39 ± 1.60 and 100.51 ± 1.21, for PA and AM, respectively. The method was validated as per the USP guidelines and showed no significant difference upon statistical comparison with reported chromatographic method.

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