I want to determine Tg of lyophilized protein solution with excipients.
I don't see any sharp changes in heat flow associating with Tg. Sometimes there is sharp change in heat flow as you can see at the first picture, but if I repeate the analysis the DSC curve would be different. What I am doing wrong? Should always the lyophilized protein solution have a glass transition between 0 °C and 200 °C?
My procedure is:
Hi Elizaveta,
Maybe if you increase the heating/cooling rate you can see the Tg. With higher rates, peaks are more pronounced but the error is greater.
I hope it could help you.
Best regards
Don't use the same sample to run a second time ramp since the sample may had irreversible changes during the first ramp. If you do use different sample for each run, make sure the sample weights are close.
Usually the heating rate used for Tg determination is 20°C/min. Also you could quench the sample in order to obtain a very amorphous solid. In the step 3 instead of cooling at -15°C/min you could take out the sample from the DSC chamber to the room temperature.
If it doesn't work out you could try yo measure the Tg on cooling, may be with a temperature program like this: Heat up from 0°C to 200°C at 10°C/min
Hold 5 min at 200°C
Cool from 200°C to -100°C
Good look.
Best regards.
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