Published: October 24, 2011 r2011 American Chemical Society 49 dx.doi.org/10.1021/op200168g | Org. Process Res. Dev. 2012, 16, 49–56 ARTICLE pubs.acs.org/OPRD Use of in Situ Raman, FBRM, and ATR-FTIR Probes for the Understanding of the Solvent-Mediated Polymorphic Transformation of IIÀI Etiracetam in Methanol Christelle Herman, †, * Benoît Haut, † S  elim Douieb, † Aur  elie Larcy, † Val  erie Vermylen, ‡ and Tom Leyssens § † Universit  e Libre de Bruxelles, Transfers, Interfaces and Processes Department, Chemical Engineering Unit, 50 Avenue Franklin D-Roosevelt, CP 165/67, 1050 Bruxelles, Belgium ‡ UCB Pharma, 60 All  ee de la Recherche, 1070 Braine l’Alleud, Belgium § Universit  e Catholique de Louvain, Institute of Condensed Matter and Nanosciences, 1 Place Louis Pasteur, 1348 Louvain-La-Neuve, Belgium b S Supporting Information ABSTRACT: The objective of the present paper is to show the utility of combining distinct online and in situ probes, tracking both the solid and the liquid phases, to come to a full understanding of the mechanism underlying polymorphic transformations. The study focuses on the batch crystallization process of etiracetam (racemic intermediate to the synthesis of levetiracetam [Keppra, UCB Pharma], presenting two enantiotropically related crystallographic forms) in methanol, as this process relies on a polymorphic transformation in solution prior to the isolation of the final compound. The polymorphic transformation is shown to follow a solvent-mediated polymorphic transformation mechanism, which is characterized by three successive phases. Identification and understanding of each of these phases requires the knowledge on the nature of the crystallographic form (Raman probe), the variations in particle size distributions (FBRM probe) as well as the solute concentration in solution (ATR-FTIR probe), showing the necessity of combining these different online analyzers. 1. INTRODUCTION 1.1. Polymorphic Transformations. One of the most fre- quently used industrial processes to achieve the required purity of active pharmaceutical ingredients (APIs) combines a solution crystallization operation, often by cooling, with a separation of the obtained crystals from the mother liquid. 1,2 Frequently, the development of crystallization processes still relies on an empiri- cal trial-and-error approach, which does not always yield a robust and optimized process. Furthermore, a lack of process under- standing may lead at later stages (scale-up or production) not only to process-related issues (e.g., caking, difficulty to determine the end point of the process, etc.) but also to inconsistency in the quality of the product. One such quality attribute, depending on the crystallization conditions, is the final crystallographic form of the solid crystals. 3 Especially for APIs, this form is of importance to avoid stability, solubility, or bioavailability issues. Moreover, it is not uncommon to observe the appearance of several crystal- lographic forms during a crystallization process. To ensure the crystallographic form of the final product, it is of importance to understand the physicochemical phenomena underlying the formation of the different crystallographic forms and the me- chanism of the polymorphic transformation leading from one form to another. Trying to understand the transformation of one form to the other can, in principle, be achieved through sampling and offline analysis, although this is tedious and often leads to a limited insight into the polymorphic transformation process, due to the complexity of this latter. Over the recent years, important advances have therefore been made in analyzing the process in situ using online process analyzers. The quality by design (QBD) guideline of the U.S. Food and Drug Administration (FDA) encourages the use of process analytical technology (PAT); online in situ probes such as focused beam reflec- tance measurement (FBRM), particle vision and measurement (PVM), Raman, attenuated total reflectance Fourier transformed infra-red (ATR-FTIR) or near infra-red (NIR) probes are nowa- days becoming common tools for process development. 4 Using these techniques, sampling is avoided and ‘on the fly’ information can be obtained. In turn, this can be directly related to changes occurring in the process. For solvent-mediated polymorphic transformation studies, many applications have been developed involving a single PAT measurement probe: ATR-FTIR, 5 NIR, 6 Raman, 7 or FBRM. 8,9 Although the use of a single measurement probe can give valuable insight into the process, understanding of complex process mechanisms often requires the simultaneous use of different probes. The feasibility of using a FBRM probe to monitor changes in the morphology of the crystals in conjunc- tion with a PVM probe 10 and a Raman spectroscopic probe 11 has been reported in literature. For the purpose of understanding the crystallization process and, more specifically, a polymor- phic transformation, it is important not only to gain informa- tion on the solid states appearing in the suspension but also to Received: June 24, 2011