Laser diffraction PSA · Calibration procedure
Certified reference material check
Measures a certified reference material (CRM) of known size distribution and checks that the D10, D50 and D90 results agree with the certificate.
PURPOSE
Why this is checked
Laser diffraction has no simple physical standard like a weight or a buffer. Measuring a material with a certified distribution proves the optics, detectors and software are giving correct sizes, and checks repeatability at the same time.
Frequency
Typically every 6 months or annually, and after service, laser replacement or relocation, as defined in your calibration SOP.
Learn how the Laser diffraction PSA worksYOU WILL NEED
Standards & tools
- Certified reference material with a traceable certificate (e.g. polydisperse glass beads covering the working range)
- Dispersant and conditions exactly as stated on the CRM certificate
BEFORE YOU START
Prerequisites
- Instrument warmed up and aligned
- Clean cell windows and a low, stable background
- CRM within its expiry date and sub-sampled as the certificate describes (often a whole vial per measurement)
PROCEDURE
Step by step
- 1Set up the measurement using the CRM certificate conditions (dispersion, refractive index, obscuration range).
- 2Measure the background.
- 3Add the CRM until obscuration is in range and allow it to disperse.
- 4Measure in replicate (commonly at least three measurements; some SOPs use three separate sub-samples).
- 5Record D10, D50 and D90 for each run and calculate the mean and %RSD.
- 6Compare the mean values with the certified values and calculate the % deviation.
RECORD
Example observation table
| Parameter | Certified (µm) | Measured mean (µm) | % deviation | Typical limit |
|---|---|---|---|---|
| D10 | 20.5 | 20.9 | +1.95 | ±5% |
| D50 | 40.1 | 40.8 | +1.75 | ±3% |
| D90 | 68.3 | 69.9 | +2.34 | ±5% |
CALCULATION
How to calculate the result
% deviation = (Measured mean − Certified value) ÷ Certified value × 100
- D50 certified = 40.1 µm; measured mean = 40.8 µm
- % deviation = (40.8 − 40.1) ÷ 40.1 × 100 = +1.75%
- D90: (69.9 − 68.3) ÷ 68.3 × 100 = +2.34%
ACCEPTANCE CRITERIA
Pass if
- Typically D50 within ±3% and D10 and D90 within ±5% of the certified values (as described in USP <429> / ISO 13320). Use the limits in your SOP and the CRM certificate.
- Repeatability typically %RSD not more than 3% for D50 and not more than 5% for D10 and D90.
IF IT FAILS
What to do
- Clean the cell, check alignment and repeat with a fresh CRM sub-sample.
- If it still fails, label the instrument 'Out of calibration' and call service.
- Assess results issued since the last passing check.
In LimsPulse · Calibration Management
LimsPulse schedules this calibration, records the result against limits, and blocks the instrument everywhere if it fails or goes overdue.