Reference value
A clearly identified measurand—such as image-based diameter or another defined quantity—with units and method.
Standards are evidence packages
A particle-size standard is more than a bottle of spheres.
The material, measurement method, uncertainty statement, distribution, concentration, handling history and intended calibration procedure collectively determine whether a silica particle product is suitable as a standard.
Uncertainty
A stated uncertainty associated with the certified or reported value, under specified conditions.
Traceability chain
Documented connection to appropriate references through an unbroken chain of calibrations or comparisons.
Fitness for purpose
Evidence that the material and certificate support the receiving method, range and decision.
Certificate audit
Review these fields before using the word “standard.”
| Field | Question to ask | Risk if omitted |
|---|---|---|
| Material identity | Is the particle amorphous silica, coated silica or another composition? | Wrong optical, density or surface behavior |
| Nominal and assigned size | Which value is nominal and which is measured? | Catalog size is mistaken for a certified result |
| Method | How was the size measured? | Method-specific diameters are compared as if identical |
| Uncertainty | What confidence and coverage statement applies? | Calibration decisions ignore measurement uncertainty |
| Distribution | Is width, standard deviation or CV reported? | A broad or multimodal population is treated as monodisperse |
| Medium and concentration | Under what conditions was the material supplied and characterized? | Stability and number concentration are misapplied |
| Lot and expiration | Which lot does the evidence cover and for how long? | Documents are detached from the actual bottle |
Calibration hierarchy
Match the standard to the instrument—not the other way around.
Silica particles may be selected for optical response, semiconductor inspection or other applications where material properties differ from PSL. But an instrument calibration method can require a particular reference material, response model or procedure. A product is not automatically interchangeable merely because its nominal diameter matches.
Questions engineers ask
Frequently asked questions
What makes a silica particle a size standard?
A commercial label is not enough. Suitability depends on the certified measurand, method, uncertainty, distribution, stability, intended use and the receiving instrument or procedure.
Does “traceable” mean zero uncertainty?
No. Traceability requires a documented chain and each link contributes uncertainty.
Sources and verification
Technical basis
- NIST traceability policy — Defines metrological traceability and emphasizes documented measurement results and uncertainty.
- NIST measurement protocols — Explains method-specific measurement and comparability issues.
- NIST TEM particle sizing — Example of method-defined nanoparticle size measurement.
Commercial specifications should be confirmed against the current Applied Physics quotation, certificate, lot documentation and product page before purchase or protocol use.
Continue the research
Related technical guidance
NIST traceability
Audit what the traceability statement actually supports.
Distribution and CV
Evaluate population width and monodispersity.
Characterization methods
Select evidence that matches the decision.
Applied Physics technical pathway
Need a particle specification reviewed?
Send the target size, medium, concentration, application, certificate requirements and shipping destination. Applied Physics can evaluate the appropriate silica family or custom pathway.