Hello,

First I would go to the website of the DSC manufacturer and look up how to process your data after the experiment (hopefully using their software). This will be best since it would involve the same software you used to obtain your data and you would not need to convert your data back and forth. From a first glance you need to do two major things (assuming you have not already done them):

1) Display your data in the same way. Have the same tranisitions (like crystallization peaks) pointing in the same direction on all graphs. This does not seem to be the case and it causes lots of confusion. I also normalize my heat flow (y-axis) by the mass of the sample so the integrals can be directly compared in terms of crystallinity, etc.

2) You should do a baseline subtraction. This could be as simple as running an empty sample pan and subtracting that data from what you have. This will flatten your baseline and hopefully remove any odd stuff NOT caused by your samples.

In addition, I would search if anyone has done DSC on your pure drug so you can see what the result should look like and compare it to yours. Hopefully this would put you in a better position to analyze your data. Good Luck.

Thanks a lot for your rapid reply @Mr. Roddel Remy. Actually my intention was to check the compatibility issue so that I can say whether polymers I used in my formulation are compatible with the drug or not. Literature also supports that the melting point of the drug-Acyclovir is 256.5-257C which nearly fits in my case as the DSC graph showed melting point at 256.33C. Now, is it possible to conclude regarding compatibility issue from the above attached graphs? Thanks again..

Thanks a lot for your simpler explanation Mr. S. Shyale. It was a great help for me...

Dear Karmoker,

Please scan the physical mixture of both acyclovir and polymer and find out the melting peak of acyclovir and also calculate the value of enthalpy changes of melting peak of acyclovir in single api scan and physical mixture. If you found melting peak in physical mixtures then you can say drug is compatible with the polymer.

Best of luck.

Thanks a lot for your concern. Hope to hear some details explanation from an expert like you. However, let me know if you need the DSC graps of other two polymers. Althoug I didn't examine them but I may collect their information from other published papers. Thanks in advance. 

I am excited to hear from you!

If we assume that the large sharp peak in the acyclovir plot is a melting endotherm - the only thing that makes sense to me - then the gradual endotherm before 100 degC may be due to loss of water or solvent by evaporation.  The large decrease of the melting temperature when the polymers are present does not necessarily mean chemical interaction, but may be due simply to partial dissolution in the polymers, which seem to have a much lower TG as pointed above by Dr. Hohne.  This depends of course on the polymer molecular weight.  Also important is what you call "physical mixing" - does it include grinding?  How much grinding?  In other words, how intimate is the mixing?

Going one step back, I'm not quite sure what you want to find out here.  If you want to find, for example, the likely shelf life of acyclovir in a capsule made of the polymers you study, going to 200+ degC will not tell you much that is useful.  The kinetics of any reaction between the solid drug and the above-glass-transition polymer will be dependent on diffusion rates and cannot be extrapolated to ambient temperatures through the polymer glass transition: The diffusion rates scale with viscosity, and the polymer viscosity is highly non-Arhenius around the glass transition.  At ambient temperatures (far below the glass transition, apparently) you might as well rub two stones together.

Two caveats to the previous statement: (a) If the gas or solvent given off near 100C interacts with the polymer, that's worth figuring out (not necessarily by DSC); (b) if what you are looking at is an early experiment in mechanochemistry, in which the reaction rate depends on grinding conditions, then it's worth varying the grinding time etc. and see what happens - but drawing direct conclusions from the DSC curves will not be easy.

Thank you so very much Mr. G. W. H. Höhne and Mr. Emanuel Cooper. Your explanation came into a great help for me. Wish you all the best. 

Thanks a lot  for your systematic and detailed explanation. It helps my  Dr. Gunther W. Hohne,e a lot to better understand the following remarkable issues ...... but, you colleague Dr.Karmoker to set a very curious matter-question!

regards