Seeding the Desired Polymorph:  Background, Possibilities, Limitations, and Case Studies

The techniques for seeding of a desired polymorph during crystallisation from solutions are reviewed. The basic information about the type of polymorphism needed to consider seeding strategies is discussed first. The development of seeding strategies is facilitated by certain data on the system. Their relevance as well as techniques for the determination are given. Reflections on the choice, characterisation, and preparation of the seed are followed by a discussion of techniques for the determination and optimisation of the seeding, that is, the rate of crystallisation and amount of seed added. Scale-up issues from the well-controlled environment of the laboratory to the plant sum up this point. The discussion of published as well as unpublished results of seeding strategies serve as illustration of the theoretical and practical considerations made.