differential scanning calorimetry

Imagine heating two tiny pans side by side at exactly the same rate — one holding your sample, one empty as a reference — and carefully tracking how much extra heat each one needs. Differential scanning calorimetry (DSC) does exactly this: it measures the difference in heat flow between sample and reference as temperature rises, revealing the energy events happening inside the material.

Whenever the sample melts, crystallizes, evaporates solvent, or transforms between solid forms, it absorbs or releases heat, showing up as a peak or step on the DSC trace (the thermogram). Melting and dehydration appear as endothermic peaks; crystallization and some decompositions are exothermic; a glass transition appears as a subtle step change in baseline rather than a peak.

In preformulation, DSC is a workhorse: it gives melting point and purity, fingerprints polymorphs and hydrates, locates the glass transition of amorphous material, estimates crystallinity, and screens drug-excipient compatibility by revealing new or shifted peaks. The honest limits are that very small or overlapping events can be missed, heating itself can induce form changes that are artifacts, and DSC tells you that an event occurred but not directly what structure caused it — so it is usually paired with X-ray powder diffraction and thermogravimetry.