Using the newly developed Anton Paar humidity chamber (MHC-trans) in combination with the fully automatic combined software control of both temperature and relative humidity, the crystallization process of spray-dried salbutamol sulfate was studied in situ. A series of timeresolved experiments under the accurately controlled temperature-humidity conditions was performed. The resulting non-ambient data sets were analyzed using PANalytical’s HighScore software. The partial least squares (PLS) regression method (implemented in HighScore 4.0) was used to quantify the amount of the amorphous salbutamol sulfate phase as a function of time. It was shown that crystallization of salbutamol sulfate strongly depends on humidity conditions and this dependence was shown to be non-linear.
Automatic combined control of temperature and humidity is a result of an ongoing collaboration between PANalytical and Anton Paar. This tool enables in situ XRD experiments at controlled temperature-humidity in a completely automatic fashion and is applicable to both MHC-trans and CHC plus+ Anton Paar chambers. The algorithm accounts for the strong correlation between all involved parameters and automatically controls humidity and temperature of the sample. Furthermore, for the CHC plus+ setup, the temperature of the chamber (= the water bath temperature) is also automatically controlled. This unique algorithm not only ensures a smooth path through the T-RH parameter space without strong deviations from the programmed profile, but also guarantees condensation-free experiments.