Fast scanning calorimetry: Sublimation thermodynamics of low volatile and thermally unstable compounds

Highlights: • A new technique for sublimation studies of thermally labile molecules is presented. • It overcomes the limitations of other methods by using fast scanning calorimetry. • The developed procedure was tested with antraquinone, theophilline and caffeine. • The absence of decomposition was confirmed by the "three purge gases"-technique. -- Abstract: Fast scanning calorimetry (FSC) was applied for measurements of the sublimation rates of theophylline, caffeine and anthraquinone as reference compounds. In comparison to conventional vapor pressure determination techniques, this method requires only nano-gram-size samples. The increased surface to volume ratio allows for very high sublimation rates and makes the sublimation process dominant over a possible decomposition. Experimental conditions and data treatment have been elaborated and validated by comparison with reliable literature data. The FSC method "opens a new door" for reliable experimental determination of vapor pressures and sublimation enthalpies for very low volatile and thermally unstable compounds like bio-relevant molecules.