PSD, BET, and dispersion: avoiding apples‑to‑oranges comparisons

A common failure mode in powder qualification is comparing numbers that were measured differently. PSD can mean sieve, laser diffraction, or DLS. BET depends on degassing and moisture. Dispersion quality can dominate viscosity and flow—but it’s often not specified at all. This guide helps you write a spec that produces consistent behavior, not just pretty COA tables.

When a qualification fails, it often traces back to one missing line in the spec: the measurement method. If PSD is measured differently (or dispersion energy is different), your powder is effectively a different material. Treat method and sample prep as part of the parameter.

PSD: three methods, three different ‘truths’

• Sieve: great for coarse cuts; limited for fine powders and agglomerates.
• Laser diffraction: sensitive to dispersion settings; results can shift with sonication and surfactants.
• DLS: measures hydrodynamic size in a liquid; can over‑weight small populations and is not directly comparable to dry PSD.

Tip: if you’re unsure which bullet is critical, tell us your process step that fails (feeding, mixing, viscosity, setting). We’ll map the failure mode to the right spec controls.

BET: what it tells you—and what it doesn’t

• BET reflects accessible surface area, not necessarily the surface ‘available’ in your formulation after agglomeration.
• Drying/storage history can change agglomeration and therefore effective surface behavior.
• Always pair BET with a dispersion note and PSD method for fair comparisons.

Tip: if you’re unsure which bullet is critical, tell us your process step that fails (feeding, mixing, viscosity, setting). We’ll map the failure mode to the right spec controls.

Dispersion: the hidden spec

• If your process depends on viscosity/flow, dispersion preparation must be defined (solvent, mixing energy, time, additives).
• Request a simple dispersion check if your application is sensitive (even a photo or sedimentation time can catch issues early).

Tip: if you’re unsure which bullet is critical, tell us your process step that fails (feeding, mixing, viscosity, setting). We’ll map the failure mode to the right spec controls.

A spec template that prevents surprises

Rule of thumb: if a parameter affects your process, include the method and sample prep in the spec. That single line saves weeks later.

Practical validation steps

• Run a small ‘incoming QC’ check that matches your real process (same mixer, same solvent, same time).
• Compare at least two lots from the same supplier before freezing the spec.
• Track moisture and storage time—many issues are packaging/handling, not chemistry.

Tip: if you’re unsure which bullet is critical, tell us your process step that fails (feeding, mixing, viscosity, setting). We’ll map the failure mode to the right spec controls.

Example spec snippet (copy/paste)

• Product: [phase/form factor]
• Particle size (PSD): [range] — Method: [laser diffraction / sieve / DLS], dispersion: [settings]
• Moisture: ≤ [x]% — Packaging: sealed, moisture-protected
• Documentation: Typical values for evaluation; Full COA for production lots on request
• Lot-to-lot variability: [acceptable ranges] for PSD/moisture/other critical items

Talk to us

Email info@kannrybio.com or use the contact form to discuss your target spec and stage (evaluation vs production). We can recommend a suitable grade and documentation scope.