Combining zone melting and preparative chromatography to purify Phenanthrene Nicolas Couvrat • Antoine Burel • Se ´verine Tisse • Yohann Cartigny • Ge ´rard Coquerel Received: 24 July 2012 / Accepted: 2 October 2012 Ó Akade ´miai Kiado ´, Budapest, Hungary 2012 Abstract The impacts of zone melting and preparative chromatography on Phenanthrene purity were established by GC and DSC experiments. On the one hand, phase diagrams investigations between Phenanthrene and its major impurities (Dibenzothiophene, Fluorene, Carbazole, and Anthracene) have revealed inadequate heterogeneous equilibria for an efficient purification by zone melting, especially for Fluorene. Nevertheless, a clear purification effect has been noticed by applying this thermal process. On the other hand, preparative chromatography has shown a propensity to separate Phenanthrene from Fluorene. This uncommon case demonstrates the advantages of combining purification techniques to reach a sufficient purity level. Moreover, this study highlights the limitations of analytical tools to quantify such high level of purity. Keywords Zone melting  Preparative chromatography  Chemical purity  Phenanthrene  Solid–solid transition  DSC analyses Abbreviations HPLC High performance liquid chromatography P-HPLC Preparative HPLC GC Gas chromatography LOQ Limit of quantification NQ Not quantifiable MS Mass spectroscopy DSC Differential scanning calorimetry LT Low temperature HT High temperature R-P Raw Phenanthrene ZM-P Zone melted Phenanthrene TP-P Twice purified Phenanthrene Introduction Reaching ultra-pure materials (i.e., chemical purity greater than 99.9 % [1]) is nowadays a requirement for organic materials, and more particularly for active pharmaceutical ingredients (API). In addition to chemical purity, structural purity of a given molecule has to be considered when amorphous state or new crystalline phases are accessible [2]. Indeed, during the synthesis of organic molecules, the presence of side products is difficult to avoid. Two main preparative methods are classically used to reach organic pure materials: (i) crystallization, which is the most com- mon separation method used at industrial scale, and (ii) chromatography via preparative HPLC, simulated moving bed technique, or supercritical fluid chromatography [3]. Crystallization methods are subdivided into two classes: in solution (solvent-assisted crystallization) and from the melt (mainly used in the field of inorganic materials) [4]. In the latter type of crystallization, the zone melting (also called zone refining) is suitable to reach ultra-pure materials. This technique was originally developed to purify germanium used in transistors [5, 6] and it is now a well-established purification method for inorganic compounds such as silicon [7]. The efficiency of the separation is directly linked to the segregation coefficient (which characterizes the repartition of Electronic supplementary material The online version of this article (doi:10.1007/s10973-012-2746-z) contains supplementary material, which is available to authorized users. N. Couvrat (&)  A. Burel  S. Tisse  Y. Cartigny  G. Coquerel Laboratoire SMS, Universite ´ de Rouen, Mont Saint Aignan, France e-mail: nicolas.couvrat@univ-rouen.fr 123 J Therm Anal Calorim DOI 10.1007/s10973-012-2746-z