Assessing stability-indicating methods for coelution by two-dimensional liquid chromatography with mass spectrometric detection.

Chromatographic analysis of trace organic impurities/degradants coeluting in the midst of active pharmaceutical ingredient can be challenging given similarities in their structures and differences in their relative levels/intensities. Conventional detection techniques such as diode array detection and mass spectrometry are often inadequate to detect/identify these residual coeluting impurities and could result in a false negative. Application of two-dimensional chromatography to address/evaluate coelution in conventional chromatography is presented. Areas of interest, usually corresponding to the main component, are transferred to secondary column/s for further separation termed as pseudocomprehensive two-dimensional liquid chromatography. Coelution, if any, in the rest of the chromatogram is monitored using conventional detectors. In this work, the use of similar and complementary phases in both dimensions is presented. The use of the same phase in both dimensions to resolve coeluting impurities (especially in the front and tail of the main component differing by orders of magnitude) is an easier alternative to finding complementary column/s, as hydrophobicity dominates reversed-phase separation. The same phase separation is practical as relative levels of impurities and main component in some transferred fractions are comparable enabling their separation. The results were confirmed using mass spectrometry. This work has significant bearing as a method assessment tool in pharmaceutical and other industries.

Simultaneous, sequential quantitative achiral-chiral analysis by two-dimensional liquid chromatography.

In general, chromatographic analysis of chiral compounds involves a minimum of two methods; a primary achiral method for assay and impurity analysis and a secondary chiral method for assessing chiral purity. Achiral method resolves main enantiomeric pairs of component from potential impurities and degradation products and chiral method resolves enantiomeric pairs of the main component and diastereomer pairs. Reversed-phase chromatographic methods are preferred for assay and impurity analysis (high efficiency and selectivity) whereas chiral separation is performed by reverse phase, normal phase, or polar organic mode. In this work, we have demonstrated the use of heart-cutting (LC-LC) and comprehensive two-dimensional liquid chromatography (LC × LC) in simultaneous, sequential achiral and chiral analysis and quantitation of minor, undesired enantiomer in the presence of major, desired enantiomer using phenylalanine as an example. The results were comparable between LC-LC and LC × LC with former offering better sensitivity and accuracy. The quantitation range was over three orders of magnitude with undesired D-phenylalanine detected at approximately 0.3% in the presence of predominant, desired L-phenylalanine (99.7%). The limit of quantitation was comparable to conventional high-performance liquid chromatography. A reversed-phase C18 achiral column in the primary and reversed-phase Chirobiotic Tag chiral column in the secondary dimension were used with a compatible mobile phase.

Development of a comprehensive near infrared spectroscopy calibration model for rapid measurements of moisture content in multiple pharmaceutical products.

Near infrared (NIR) spectroscopy has been widely used for the determination of water content in a wide variety of samples. With few exceptions, all methods employ a calibration model developed and applicable for a single product. The current study describes a NIR method using a single, comprehensive calibration model to predict the water content in tablets containing different active pharmaceutical ingredients (API). The calibration model was developed for water content range of 2-13% (w/w) using tablets containing three different APIs and different formulation compositions. To develop a robust comprehensive model, individual calibration models were sequentially developed starting from a simple model for one product to including tablets from all three projects in the final model using partial least square analysis method. Data pretreatments and spectral region selections were performed during the method development to optimize the number of factors and the correlation coefficients for cross-validation and prediction by the comprehensive model. The model reliably predicted the water content in tablet samples of these three products, and can be updated for water measurements of new drug products by adding to the model two samples of the new product for calibration purpose.