Diluent blank
Measure background before adding particles.
Method split
Light scattering and light extinction are not the same
| Method | ISO reference | Typical ISO abstract range | Important response factor |
|---|---|---|---|
| Light scattering liquid-borne | ISO 21501-2:2019 | 0.1–10 µm | Particle and liquid refractive indices influence optical-equivalent size |
| Light extinction liquid-borne | ISO 21501-3:2019 | 1–100 µm | Particle blocks or attenuates light; pharmaceutical liquid applications are included |
Sample preparation
Control the dilution chain
Volumetric accuracy
Use calibrated devices within their useful range.
Mixing
Define a repeatable resuspension method.
Bubbles
Avoid counting gas bubbles as particles.
Adsorption
Evaluate loss to containers and tubing.
Hold time
Control settling and concentration drift.
Size and count controls
Use the right product for the right check
A concentrated size standard can support a calibration preparation when diluted under a validated method. A ready-to-use count control can support routine performance monitoring. Neither automatically replaces the other.
Size standards
Focus on certified mean, uncertainty and distribution.
Count controls
Focus on defined number concentration, sampling volume and repeatable routine use.
Practical worksheet
Record what changes the result
- Instrument model, serial number, firmware and method.
- Liquid matrix, temperature and background count.
- PSL lot, certified diameter and concentration basis.
- Dilution steps, devices and operators.
- Mixing, sonication or inversion procedure.
- Sample volume, flow rate and replicate sequence.
- Acceptance criteria and uncertainty.
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.