Janani S.K.

The DSC curve shows a shift of the baseline around 77°C, indicating "glass transition". Also, an exothermic peak is observed around 130°C, indicating an exothermic reaction caused by crystallization. The endothermic peak observed at around 157.89°C refers to an endothermic reaction by "melting".

Hope this will be helpful to you

Thank you Kashif Ameer Sir. So can I consider 157.89°C endothermic peak for determining the purity of the compound?

Thank you

Janani S.K.

Yes you can consider this 157.89°C endothermic peak for determining the purity of the compound as there is no published report available on this particular compounds so this is your finding

Kashif Ameer Thank you sir.

If the there is any melting taking place, then it is almost certainly accompanied by significant decomposition. Thus, (1) purity determination cannot be performed and (2) melting point/enthalpy are also incorrect. This DSC trace seems more like a multistep decomposition. The sudden heat flow jump @ cca 155°C looks like a rupture of a hermetically sealed Al crucible (if such crucible was used).

Tibor Dubaj thank you. But in most of the literature i have observed the same pattern of graph. I have attached one of the reference article. Can you please find the article and help me out?

Thanks.

Reference article:

Ansari MT, Imran M, Hassan SS, Tariq I, Murtaza G. Solubility enhancement of dihydroartemisinin using mixture of hydroxypropyl-β-cyclodextrin and PEG-6000. Lat Am J Pharm. 2014 Jan 1;33(3):483-91.

As written in the paper you referenced: "DHA did not exhibit any melting endotherm. Instead, an exotherm at 170.0 °C was apparent..."

I would say that the rest of the discussion ("including melting onset Tonset = 159.20 °C") is quite dubious. Without direct observation of the sample during heating (e.g. by melting point apparatus or hot stage microscopy) I would not conclude that DHA melts around 159 °C.

There are three possibilities: (1) sample melts and remains stable in liquid; (2) sample melts and decomposes in liquid; (3) sample decomposes in solid before any melting occurs.

Strictly speaking, only in case (1) the melting point is defined. In case (2) the melting point can be measured/observed, however, it is not a purely thermodynamic parameter (that is, related to equilibrium). Cases (2) and (3) are very common for organic substances, especially with those with higher molecular weight.

What data are you trying to obtain from the DSC record?

Thank you for the explanation @ Tibor Dubaj . I wanted to confirm the purity of the compound.

Further, I think if determine the melting point of the compound using melting point apparatus, it would be much better.

Thank you.

Purity determination by DSC is only possible in case (1) when solid-liquid equilibrium is observed at quasi-static conditions (slow heating). DHA purity must be determined by some other method (e.g. HPLC).