Quantification of caffeine and loperamide in printed formulations by infrared spectroscopy

Printing technology serves as a valuable alternative for improving the flexibility and dosing precision of drugs in the fabrication of solid dosage forms. Nevertheless, there is a need for applicable control methods to ensure the final quality of printed products. In this study the use of attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy in the quantitative analysis of printed formulations was investigated. Piezoelectric inkjet printer was used to prepare formulations containing caffeine and loperamide hydrochloride with different doses by varying the resolution of the printing. The ATR-FTIR spectral data were plotted against the printed drug content as well as against drop spacing (resolution). The results from the univariate data analysis showed that the correlations between the height or area of a single peak in the corresponding spectra and drop spacing were linear, whereas with the drug content they were logarithmic. The Partial Least Squares regression models of the spectra for the quantification showed good predictability. Furthermore, the predictive properties of the calibration models were improved by optimizing the scaling methods, spectral range selection and data pre-processing. In conclusion, this study demonstrates the applicability of infrared spectroscopy together with univariate/multivariate data analysis for the quantitative quality control of printed formulations.