Spectrophotometric Determination of Drug Concentrations

An HP Agilent 8453 spectrophotometer (Agilent Technologies, Santa Clara, CA, USA) was used to determine of the model drug (TH or SA) concentration in the dissolution samples [44 (link),45 (link),46 (link),47 (link)] The absorbance values of the samples withdrawn at the predetermined times were measured against the corresponding blank sample using the fixed-wavelength method. A wavelength of 272 nm for TH and 298 nm for SA together with three-point background correction were applied. The used wavelengths corresponded to the absorption maximum of the model drugs. The validity of the Lambert–Beer law was verified in the expected range of the drug concentrations. To transform the absorbance values into the concentrations and percentages, the calibration-curve method was used.