Use of near-infrared for quantitative measurement of viscosity and concentration of active ingredient in pharmaceutical gel.

Near infrared (NIR) spectroscopy is gaining worldwide interest as an analytical tool for quality control of raw materials, intermediate products, and final dosage forms. This technique can be used without sample preparation, therefore, avoiding the need for reagents and solvents. Quantitative NIR analyses involve calibration by sophisticated mathematical techniques that have been used extensively since the advent of microcomputing and chemometrics. The main objective of this investigation was to use transmission near-Infrared spectroscopy to measure the potency of an active ingredient in a topical gel preparation. A second objective was to evaluate the effect of gel viscosity on the NIR reflectance spectra. Four gel formulations with different ibuprofen concentrations were used for quantitative determination of the active ingredient, and five gel formulations with different viscosity values were used for the evaluation of the effect of viscosity change on the near-infrared reflectance spectra. The laboratory ibuprofen quantitative determination was compared to near-infrared transmission data using linear, quadratic, cubic and partial least square techniques to determine the relationship between ultraviolet (UV) determination and near-infrared spectra. For viscosity, the laboratory data were compared to near-infrared diffuse reflectance data using the same techniques used to determine the relationship between Brookfield viscometer determination and near-infrared spectra. The results demonstrated that an increase in ibuprofen concentration and viscosity produced an increase in near-infrared absorbance. Series of model equations were developed from the calibration of laboratory vs. the near-infrared data for each formulation. The near-infrared spectroscopy method is an alternative method that does not require sample pretreatment for quantitative measurement of active ingredient and viscosity of pharmaceutical gel.