Glucose, monohydrate and the anhydrous form
Glucose, monohydrate
Measuring cells: DSC820 or TGA850
Pan: Aluminum 40 µl or 100 µl, both with pierced lids
Sample preparation: As received, no preparation
DSC measurement: Heating from 30 °C to 250 °C at 20 K/min
TGA measurement: Heating from 30 °C to 300 °C at 20 K/min
Atmosphere: Nitrogen, DSC: 50 cm3/min, TGA: 80 cm3/min
Glucose can exist as the monohydrate or in the anhydrous form. The TGA curves show that the two forms differ quite distinctly from one another. The anhydrous form shows no loss of moisture, whereas with the monohydrate the elimination of water can be observed. This results in a step of about 7% and is slightly below the value of 9.1% expected stoichiometrically.
The weight loss is determined.
Sample | Step, % | Evaluation range, °C |
---|---|---|
Monohydrate | 7.1 | 42-145 |
Anhydrous form | <0.1 | 42-145 |
The anhydrous form exhibits only the melting process at about 161 °C. The monohydrate shows a very broad peak resulting from the elimination of water and the transformation to the anhydrous form. This then melts at about 158 °C. The smaller heat of fusion and lower melting point in comparison with the anhydrous form, indicate an incomplete crystallization.
The onset temperatures and peak areas are determined.
Sample | First peak | Second peak | ||
---|---|---|---|---|
Onset, °C | ΔH, J/g | Onset, °C | ΔH, J/g | |
Monohydrate | 71.4 | 52.6 | 153.9 | 162.4 |
Anhydrous form | - | - | 160.9 | 198.7 |
The DSC and the TGA curves allow the identification of the monohydrate and anhydrous forms.
Pseudopolymorphism, Glucose Monohydrate | Thermal Analysis Application No. HB834 | Application published in METTLER TOLEDO TA Application Handbook Pharmaceuticals