The potential of high speed DSC (Hyper-DSC) for the detection and quantification of small amounts of amorphous content in predominantly crystalline samples

Abstract

The purpose of this study was to explore whether it is possible to use hyper differential scanning calorimetry (HDSC) to detect and quantify low levels of amorphous content in samples that are mostly crystalline. HDSC uses scan rates that are much faster than conventional DSC, and consequently results in greater sensitivity. It was found that with every increase in scan rate it became easier to detect the glass transition ( T g) response. Scanning at 500 °C/min was possible and this gave such great sensitivity that very low sample mass (ca. 1 mg) could be used without any loss in detection of T g. Mixtures of crystalline and amorphous (spray dried) lactose were prepared and scanned at 500 °C/min. It was observed that the T g response was easily detected even for samples that contained 1.5% amorphous content when using very low samples mass. The view held at present is that DSC is not well suited to studies of amorphous content if the sample contains 10% or less of the amorphous material. The data generated here show that much better detection sensitivity is possible when using the rapid scan rates. As well as being able to detect the presence of very low amorphous contents it was also possible to obtain a quantification, as a linear response was obtained for the step height change in heat flow as a function of amorphous content. It was concluded that HDSC provides a method of obtaining a very fast assessment of the presence of amorphous form, the possibility to quantify this and the need to use a very low sample mass. The combination of speed, low sample mass and sensitivity makes this a very valuable technique for studies on partially amorphous samples.