Polymorphic Modifications by Annealing, Butylated Hydroxyanisole - METTLER TOLEDO

Polymorphic Modifications by Annealing, Butylated Hydroxyanisole

SampleButylated hydroxyanisole

Butylated hydroxyanisole

 

Application

Inactive ingredient (antioxidant)

 

Conditions

Measuring cellsDSC820

Pan: Aluminum 40 µl, hermetically sealed

Sample preparation: As received or annealed beforehand

DSC measurement: A) Heating from 30 °C to 70 °C at 2.5 K/min, B) Heating from 35 °C to 60 °C, held isothermally for 10 min at 60 °C, then cooling to 30 °C

Second heating run from 30 °C to 70 °C at 2.5 K/min

Atmosphere: Nitrogen, 50 cm3/min

 

Interpretation

The untreated sample shows two melting peaks with a recrystallization step. The annealed sample exhibits just one melting peak. Annealing at a temperature slightly above the onset of the melting range of the first modification forces the sample to crystallize to the other form. As application 4 shows (page 22), the heat of fusion ΔH of the first modification is about 100 J/g and that of the second form (from this example) only 84.5 J/g. With monotropic systems, the heat of fusion ΔH of the first peak is larger than that of the second peak. Consequently in this case it could be an enantiotropic system. In order to clarify the situation, a measurement at about 60 °C with the hot stage microscope (FP84/85) should be performed. In an enantiomeric system no liquid phase is formed between the two endotherms. If a liquid phase appears, then this is a monotropic system and the substance (curve B) was not 100% crystalline.

 

Evaluation

The onset temperatures and the enthalpy changes are determined. The values that can not be determined with certainty because of the overlap of the melting and recrystallization processes are shown in brackets. In the case of sample B only the second heating run is shown and evaluated.

SampleOnset, °CΔH, J/gOnset, °CΔH, J/g
A (untreated)59.3(73.5)63.0(27.0)
B (10 min at 60 °C)--62.784.5

 

Conclusion

Unfavorable storage or processing conditions of a substance can lead to crystal modification changes, especially when the transition temperature lies close to the storage or processing temperature.

 

Polymorphic Modifications by Annealing, Butylated Hydroxyanisole | Thermal Analysis Application No. HB829 | Application published in METTLER TOLEDO TA Application Handbook Pharmaceuticals