VIBRATIONAL SPECTROMETRY FOR THE ASSESSMENT OF ACTIVE-SUBSTANCE IN METOPROLOL TABLETS - A COMPARISON BETWEEN TRANSMISSION AND DIFFUSE-REFLECTANCE NEAR-INFRARED SPECTROMETRY

Near-infrared spectrometry (NIR) was used to quantify metoprolol succi nate in controlled release tablets. Metoprolol tablets were made accor dingly to an experimental design using different strengths around a ce ntral strength of 47.5 mg per tablet. A comparison was made between NI R in the diffuse reflectance mode and the transmission mode. This show ed that, although a narrower wavelength range was available in the tra nsmission mode, predictions were much better for models based on trans mission spectra than for models based on diffuse reflectance spectra. The main reason for this is that in the reflectance mode NIR spectrome try is very sensitive to the inhomogeneity of the material, while in t he transmission mode this problem is less severe. This is due to the l arger volume of the material scanned in the transmission mode compared to that in diffuse reflectance. Spectra were taken before and after t he tablets were stored under humid conditions. This allowed the final calibration models to be made more robust towards variations in the am ount of water in the tablet. Different batches of metoprolol pellets a nd microcrystalline cellulose were used during the production of the t ablets. This resulted in models that were more robust towards possible batch-to-batch differences in the main constituents.