Crystal Polymorphism: Same Chemical Composition Can Have Different Solid Structures

Define the Phase or Process Boundary

IUPAC's polymorphic-transition definition distinguishes crystalline phases of the same chemical composition but different crystal structures. A chemical assay result alone therefore does not establish that two solids have the same crystalline form.

Review a Hypothetical Comparison

Consider two fictional lots with the same named compound and reported chemical assay 99.0%. Their independent structural records identify Form I in one and Form II in the other. The matching assay does not resolve that difference. Conversely, a new external needle-like appearance alone is not a structural identification: crystal habit and lattice arrangement answer different questions.

Keep the Evidence with the Decision

Keep chemical-composition evidence and structural-form evidence in separate fields. Record mixtures of forms and the state/history under which the solid is handled. If a comparison depends on form stability, ask for actual form-specific evidence rather than transferring a property from the compound name alone. Preserve unknown or mixed form instead of assigning a label from appearance.

The lot records are invented. This article does not choose an analytical instrument, infer pharmaceutical suitability, predict form stability or supply a phase-transition temperature.

Does the proposed process comparison preserve the actual solid form rather than only chemical identity?

This blank worksheet is for your own project. It contains no H M machine trial result.

Customer Questions

Primary References

These references support the technical principles discussed in this guide. The worked examples and review questions are educational.

• IUPAC's polymorphic-transition definition
• Reference from hmpharmamachines.com