Application of quality by design to the development of analytical separation methods

Recent pharmaceutical regulatory documents have stressed the critical importance of applying quality by design (QbD) principles for in-depth process understanding to ensure that product quality is built in by design. This article outlines the application of QbD concepts to the development of analytical separation methods, for example chromatography and capillary electrophoresis. QbD tools, for example risk assessment and design of experiments, enable enhanced quality to be integrated into the analytical method, enabling earlier understanding and identification of variables affecting method performance. A QbD guide is described, from identification of quality target product profile to definition of control strategy, emphasizing the main differences from the traditional quality by testing (QbT) approach. The different ways several authors have treated single QbD steps of method development are reviewed and compared. In a final section on outlook, attention is focused on general issues which have arisen from the surveyed literature, and on the need to change the researcher's mindset from the QbT to QbD approach as an important analytical trend for the near future.