In contrast to isocratic separations, gradient elution can sometimes seem to be counter-intuitive. Yet with the proper perspective, the things we intuitively understand about isocratic methods apply in a similar manner to gradients.
The removal of azide as a potential impurity from a drug substance may be critical to its safety profile. The quantitation of this impurity is an important control parameter. This article describes a simple and practical assay for azide using chemical derivatization and HPLC. The method is shown to be suitable for the intended purpose on three example test materials. Potential issues for wider applications are discussed.