Short answer: Particle-standard preparation can introduce more error than the standard itself. Contaminated containers, uncontrolled mixing, adsorption, incorrect dilution calculations and unsuitable water or surfactant can change the delivered population and invalidate the instrument check.
Decision rule: Follow the manufacturer’s instructions and the validated instrument method. Do not improvise a generic dilution because two products share the same nominal size.
Inspect the product and documentation
Verify lot, nominal and assigned size, concentration, expiration or retest information, storage condition and certificate. Confirm that the material and concentration match the procedure before opening the container.
Control cleanliness of the preparation path
Use clean containers, pipettes and water or diluent appropriate to the method. Prepare in an environment that minimizes background particles. Label every intermediate dilution and avoid reusing tools across sizes without the approved cleaning process.
Mix without damaging the preparation
Particles can settle or concentrate over time. Use the manufacturer’s recommended resuspension method and duration. Aggressive mixing can introduce bubbles, contamination or changes in agglomeration. Record the mixing step because timing can affect repeatability.
Document the dilution calculation
Record stock concentration, target concentration, volumes, dilution steps and uncertainty contributors. Use a second-person check or validated worksheet for critical preparations. A correct final number with an undocumented path is weak evidence.
Manage hold time and disposal
Define how long the prepared dilution can be used, how it is stored and when it is discarded. Do not assume an intermediate dilution has the same stability as the original product. Avoid returning unused material to the stock bottle.
Working checklist
- Correct lot and certificate
- Approved diluent
- Clean container and tools
- Resuspension method
- Documented dilution calculation
- Intermediate labels
- Preparation time and hold limit
- Disposal and stock-bottle protection
What to include in the RFQ
State the particle size, stock concentration or desired use concentration, instrument method, required volume, certificate needs and any special packaging or storage constraints.
Use the GSE technical RFQ to submit the requirement, attachments, destination and required-on-site date.
Make the preparation traceable
Record lot number, expiration or retest date, storage history, mixing method, dilution calculation, diluent identity, containers, pipettes and the person preparing the sample. Label every intermediate dilution. Without that chain, an unexpected count result can be impossible to investigate.
Use only the preparation instructions approved for the method and certificate. Aggressive shaking, unsuitable surfactant, contaminated water or prolonged storage of a working dilution can alter the result. Prepare only the quantity needed unless the procedure establishes stability.
Continue the topic: Particle Metrology Knowledge Center.
Authoritative references
This guide translates public requirements and technical concepts into purchasing and study-planning questions. The controlling standard, regulation, site procedure and quality approval remain authoritative.
Frequently asked questions
Can PSL suspensions simply be shaken hard?
Use the manufacturer’s recommended mixing method. Excessive agitation can introduce bubbles or other preparation problems.
Can unused diluted standard be returned to the stock bottle?
That should generally be avoided because it can contaminate or change the stock; follow the approved procedure.
Why record the full dilution path?
It allows review of calculations, volumes, timing and preparation controls when results are unexpected.
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