Oxidation Stability of Oils

Sample

Maize oil, fresh and old

Application

Inactive ingredient (solvent for active ingredients)

Conditions

Measuring cell: DSC821^e

Pan: Aluminum 40 µl, without lid or copper 40 µl, without lid

Sample preparation: Pan filled with sample using a syringe

DSC measurement: Heating from 25 °C to 300 °C at 10 K/min resp. isothermal at 125 °C

Atmosphere: Oxygen or air, 80 cm³/min

Interpretation

The oxidation stability of oils is often measured with DSC. The measurement is performed dynamically or isothermally. The beginning of the exothermal oxidation is called the onset and characterizes the oil. In a dynamic experiment this is given in degrees Celsius and in an isothermal measurement as the induction time in minutes. Important factors influencing the onset are the material used for the pan (copper acts as a catalyst) and the atmosphere (oxygen is more reactive than air). Under the same measurement conditions, the ‘old oil’ shows an onset temperature lower than that of the fresh oil sample i.e. it is already partially oxidized.

Evaluation

Oxidation stability is characterized by determining the onset. The slight drift in the curve in the dynamic experiment, which has no effect on the evaluation, is caused by the beginning of evaporation of low molecular weight components in the oil. At 140 °C this loss amounts to approximately 0.4%.

Conclusion

The oxidation stability of oils can be investigated with DSC. The experimental conditions must be carefully chosen and kept constant in order to obtain reproducible and comparable results. The measurement can also be performed in a high pressure DSC in order to avoid early evaporation of volatile components.

_{Oxidation Stability of Oils | Thermal Analysis Application No. HB826 | Application published in METTLER TOLEDO TA Application Handbook Pharmaceuticals}