Hill, Vivienne Lucy; (1999) An investigation into the use of MTDSC as a technique for the characterisation of pharmaceutical materials. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Modulated temperature differential scanning calorimetry (MTDSC) has been investigated as a technique for analysing pharmaceutical systems. Early studies have indicated that MTDSC may have advantages compared to conventional DSC and so the aim of this project is to assess both the potential and limitations of the technique for the analysis of samples of pharmaceutical interest. MTDSC uses a sinusoidally oscillating temperature programme and results in the measurement of a modulated heat flow signal. This signal can be used to determine the reversing and non-reversing nature of the heat flow response. However, the complex heating programme makes the quality of data obtained highly dependent on the choice of experimental parameters. Therefore, the investigation was begun by systematically investigating a number of experimental parameters to determine their effect on the distortion of the modulation, the accuracy of the heat capacity data and the outcome of the deconvolution process. This study was performed using spray dried lactose as a model pharmaceutical system and aluminium oxide as a heat capacity standard. The lactose study illustrated that MTDSC could deliver improved glass transitions measurements and so it was decided to further the investigation of the technique using a more complex amorphous pharmaceutical system. Poly(d,1- lactide) was chosen and was obtained in a high and low molecular weight form. Microspheres were manufactured using a solvent evaporation technique and then MTDSC was used to determine the effect of molecular weight on the glass transition temperature. Progesterone-loaded microspheres were also manufactured. MTDSC analysis showed that at low drug loadings the progesterone was present as a glass solution. At intermediate loadings, the drug was additionally present in an amorphous form that exhibited a glass transition and crystallisation on heating. MTDSC was able to detect this glass transition when it was not possible using DSC. At high loadings the drug was present as crystals.

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