Ethanol Water Mixtures

Sample

Ethanol 99.5% p.a., distilled water to prepare 60%, 40%, and 20% ethanol solutions by volume.

Whiskey, Tullamore Dew brand, Tullamore Dew Company, Dublin, Ireland, 40% volume

Conditions

Measuring Cell: DSC30

Pan: Aluminum standard 40µl, hermetically sealed

Sample Preparation: Samples weighed at room temperature (16±2 mg), hermetically sealed, frozen at max. cooling rate by inserting the pan into the precooled DSC cell and kept isothermicly for 5 -10 minutes at -160ºC

DSC measurement: Heating from -160ºC to +20ºC at 10 K/min

Interpretation

The thermodynamic 'abnormalities' of ethanol/water mixtures, which have been measured until now by laser Raman or proton magnetic resonance spectroscopy, can be observed by DSC.

The 99.5% ethanol sample shows an exothermic crystallization peak at -123ºC and a melting peak at -105ºC. This curve shape is observed only at concentrations between 98% and 100%. 

The 60% ethanol/water mixture shows an exothermic peak at -85ºC. Similar behavior is observed for ethanol/water mixtures from 10% to 85%. As in the case of the 99.5% ethanol sample, recrystallization of the ethanol/water mixture is assumed. The melting peak of the mixture lies at -60.7ºC.

Conclusion

This example is intended to demonstrate that on the one hand even complex freezing and thawing processes can be monitored by DSC, and that on the other hand, all the phase transitions are readily apparent. Above all, the freezing and thawing behavior of free water and aqueous products can be investigated by DSC. 

^{Ethanol Water Mixtures | Thermal Analysis Application No. HB1005 | Application published in METTLER TOLEDO TA Application Handbook Food}