Feasibility study of diffuse reflectance and transmittance near infrared spectroscopy for rapid analysis of ascorbic acid concentration in bilayer tablets using a high-speed polychromator-type spectrometer

The feasibility of real-time release testing of bilayer tablets was investigated using near infrared (NIR) spectroscopy. The newly developed polychromator-type NIR spectrometer was used to compare the diffuse reflectance (DR) and transmittance (Tr) NIR spectroscopic techniques. This spectrometer not only performs highly sensitive NIR measurements but also yields the NIR spectra of an intact tablet on a millisecond (ms) timescale; i.e. 500 ms for the DR-NIR measurements and 400 ms for the Tr-NIR measurements. The bilayer tablets were prepared with the first layer comprising 0-10% ascorbic acid (AsA), 20% corn starch, 5% talc, 30% microcrystalline cellulose and 45-35% lactose, and the second layer comprising 20% corn starch, 5% talc, 30% microcrystalline cellulose and 45% lactose; their DRand Tr-NIR spectra were acquired from both sides of the tablet. With these spectra, the feasibility of DR-and Tr-NIR spectroscopy for the quantitative analysis of AsA in the bilayer tablets was compared. The DR-and Tr-NIR spectra of the bilayer tablets and their secondderivative spectra were studied. The AsA bands were not identified in the DR-and Tr-NIR spectra. However, the AsA bands at 995 nm and 1458 nm were observed in the second-derivative spectra. All the developed regression models predicted the AsA concentration, and regression vectors indicated that the prediction was based on the AsA bands. In addition, the model using the Tr-NIR spectra was able to predict the AsA concentration, even when the bilayer tablet was flipped.