Measurement of amorphous indomethacin stability with NIR and Raman spectroscopy

The recrystallisation of amorphous indomethacin (IMC) has been investigated using NIR and Raman spectroscopy and differential scanning calorimetry (DSC). Two methods were used to prepare the amorphous state (ball-milling, and melting and quench-cooling) and samples were stored under three sets of conditions (25 °C dry, 40 °C dry and 40 °C at 75% RH). The recrystallisation of amorphous IMC was quantified by DSC and compared to trends observed using Raman and NIR data. It was found that the multivariate analysis of Raman data agreed better with DSC data than univariate NIR or Raman analyses, or multivariate NIR analyses. The quenched-cooled samples were spiked with crystalline seeds (0 and 5%) and the rates of recrystallisation compared with ball-milled samples. It was found that the ball-milled samples rapidly recrystallised (within 20 days) but quench-cooled samples retained amorphous content for 20 days, even when spiked with γ-IMC to 5% (w/w) level.