Purity determination of 8-hydroxyquioline aluminum by differential scanning calorimetry

The purity of small-molecule electroluminescents (ELs) was generally determined by chromatography. However, the accuracy of results by chromatography sometimes is unsatisfactory due to systematic errors. In present work, an improved method by using differential scanning calorimetry (DSC) was employed to determine the purity of 8-hydroxyquioline aluminum (Alq3), one of the most important small-molecule ELs. A detailed study on the thermal stability and polymorphism revealed that Alq3 undergoes volatilization and phase transition during melting. The effects of volatilization and polymorphism were greatly reduced via employing volatile pans and annealing close to melting point. Then the purity of Alq3 was determined and compared with that by high performance liquid chromatography. The reproducibility and accuracy of purity determination by DSC suggest that this method could be widely applicable for small-molecule ELs, combining with the chromatography.