Charting a Path to Purity

A new book, Analysis of Drug Impurities, helps analytical chemists understand the challenges and techniques related to the accurate identification and measurement of impurities in drug products. Eight of the book's chapters were contributed by experts from Big Pharma and the US Food and Drug Administration.

The first two chapters provide solid introductions to the origin, control, and measurement of impurities in drug substances and products.

A particularly interesting chapter covers the low-level measurement of potent toxins. The author describes the significant challenge involved in the analysis of these typically low- or sub-ppm-level impurities. The chapter explains gas chromatography (GC), high-performance liquid chromatography (HPLC), thin-layer chromatography, and other analytical techniques. He offers specific examples and reviews the available options.

Sanjay Garg

Contributing author Gary E. Martin offers a helpful algorithm for impurity identification in Chapter 5. His discussion of analytical techniques emphasizes the characterization of impurities.

Chapter 6 discusses chromatography and on-line structure elucidation using spectroscopy. Its section about LC–mass spectrometry (MS), LC–nuclear magnetic resonance (NMR), and other related techniques is easy to understand, provides helpful examples, and describes many practical issues.

An interesting map in Chapter 7 provides instructions for the preparative isolation of impurities. Impressive flow diagrams present information about impurity isolation, identification, work flow, method development scouting, and task performance. The diagrams help the reader put various tasks and operations in perspective.

Chapter 8 examines the differences between analytical strategies for batch versus continuous processing with reference to techniques such as infrared, near infrared, NMR, and MS.

Analysis of Drug Impurities, Richard J. Smith and Michael L. Webb, Eds., Blackwell Publishing, Oxford, UK, 2007, 288 pp., ISBN 978-1-4051-3358-6

The book would have benefited from a full chapter each about the regulatory issues involved in the treatment of impurities and one about simple techniques such as HPLC. Overall, Analysis of Drug Impurities is a strongly recommended reference for any laboratory that handles impurities.

Sanjay Garg is an associate professor and deputy head of the School of Pharmacy at the University of Auckland, New Zealand, and a member of Pharmaceutical Technology's Editorial Advisory Board, tel. 164 9 373 7599 ext. 82836, s.garg@auckland.ac.nz