Certificate hierarchy
Seven fields that matter
| Field | Why it matters | Red flag |
|---|---|---|
| Lot / batch identity | Connects the document to the material used | Generic certificate with no lot relationship |
| Certified mean or peak | Provides the reference value | Only nominal size shown |
| Uncertainty | Shows quantified doubt in the result | No uncertainty or unclear confidence basis |
| Distribution / CV | Describes population width | “Monodisperse” with no numeric support where resolution matters |
| Measurement method | Explains how size was assigned | Method outside its useful size range or not stated |
| Concentration / solids | Supports dilution, count or challenge calculations | Units or basis unclear |
| Traceability statement | Defines the documented reference chain | “NIST certified” marketing phrase without chain details |
Uncertainty
Do not confuse uncertainty with particle distribution
Measurement uncertainty describes doubt associated with the assigned value. Standard deviation or CV describes the spread of the particle population. They answer different questions.
| Metric | Question answered |
|---|---|
| Expanded uncertainty | How confidently is the certified mean known under stated conditions? |
| Standard deviation | How widely are individual particle diameters distributed? |
| Coefficient of variation | What is the distribution width relative to the mean? |
| Tolerance / acceptance limit | What range will the user’s procedure accept? |
Fit for purpose
Traceable does not automatically mean suitable
NIST’s policy is explicit: traceability alone does not guarantee fitness for purpose. The uncertainty must be sufficiently small for the measurement need.
A standard can have excellent documentation and still be wrong for an instrument if the medium, refractive index, concentration, size node or preparation path does not match the method.
Receiving checklist
Before releasing the lot for use
- Match product, lot and certificate.
- Verify the bottle is within expiration and storage conditions were maintained.
- Check the certified node against the procedure and instrument range.
- Confirm uncertainty and distribution meet acceptance criteria.
- Record concentration, fill volume and any dilution basis.
- Archive the certificate with the test or calibration record.
Applied Physics technical pathway
Match the standard to the measurement—not the other way around.
Send the instrument, medium, target size, concentration, certificate and packaging requirements to Applied Physics for a technical recommendation.