LimsPulse
Liquid particle counter · Calibration procedure

Sizing calibration with certified spheres

Calibrates the size thresholds of the light obscuration sensor using monodisperse polystyrene spheres of certified diameter, and checks sensor resolution.

PURPOSE

Why this is checked

The counter does not measure size directly; it measures how much light each particle blocks. Certified spheres link signal height to size so the 10 µm and 25 µm channels count the right particles.

Frequency

At least annually, or as the current chapter and your SOP require, and after sensor replacement or repair.

Learn how the Liquid particle counter works
YOU WILL NEED

Standards & tools

  • Certified monodisperse polystyrene spheres of several sizes covering the range (e.g. about 5, 10, 15 and 25 µm), traceable to a national standard
  • Particle-free water
BEFORE YOU START

Prerequisites

  • Sensor flushed and blank counts low
  • Sample volume accuracy and flow rate already verified
PROCEDURE

Step by step

  1. 1Dilute each sphere suspension in particle-free water to a concentration well below the coincidence limit.
  2. 2Run each suspension and record the pulse-height (or channel) at the peak of the response.
  3. 3Build the calibration curve of signal height against sphere diameter in the software.
  4. 4Check sensor resolution with the 10 µm spheres from the width of the response distribution.
  5. 5Re-run the 10 µm spheres as unknowns and confirm the indicated size.
RECORD

Example observation table

Certified sphere (µm)Indicated mean size (µm)% error
5.05.1+2.0
10.010.2+2.0
15.014.8−1.3
25.025.3+1.2
CALCULATION

How to calculate the result

% sizing error = (Indicated size − Certified size) ÷ Certified size × 100
  1. 10.0 µm spheres read as 10.2 µm
  2. % error = (10.2 − 10.0) ÷ 10.0 × 100 = +2.0%
ACCEPTANCE CRITERIA

Pass if

  • Indicated size of the certified spheres within the tolerance in your SOP and the current chapter.
  • Sensor resolution typically not more than 10% (see USP <788> / Ph. Eur. 2.9.19 for the exact procedure).
IF IT FAILS

What to do

  • Clean the sensor and repeat the calibration.
  • If it still fails, label the counter 'Out of calibration' and contact service; the sensor may need replacement.
  • Assess particulate results reported since the last valid calibration.
MORE

Other Liquid particle counter calibrations

In LimsPulse · Calibration Management

LimsPulse schedules this calibration, records the result against limits, and blocks the instrument everywhere if it fails or goes overdue.

See how