Endotoxin reader · Calibration procedure
Temperature and photometric checks
Verifies that the reader holds all wells or tubes at 37 ± 1 °C and that its absorbance readings at 405 nm (or turbidity readings) agree with certified reference filters or plates.
PURPOSE
Why this is checked
The LAL reaction rate depends strongly on temperature, and the onset time depends on the measured optical density. Uneven heating or a photometric error shifts onset times and so changes the endotoxin result. These checks confirm the reader is fit for USP <85> kinetic methods.
Frequency
Typically every 6–12 months, and after repair or relocation, as defined in your SOP.
Learn how the Endotoxin reader worksYOU WILL NEED
Standards & tools
- Calibrated temperature probe or temperature verification plate traceable to national standards
- Certified neutral-density filter plate or absorbance reference standards at 405 nm
- Manufacturer's verification software or test plate, where provided
BEFORE YOU START
Prerequisites
- Reader switched on and at temperature for the manufacturer's warm-up time
- Optical path clean
PROCEDURE
Step by step
- 1Temperature: place the calibrated probe(s) in representative wells (corners and centre) or tube positions with LRW and let them equilibrate.
- 2Record the temperature at each position and compare with 37 °C.
- 3Photometric: read the certified filter plate at 405 nm and record each value.
- 4Calculate the error against the certified value for each filter.
- 5For tube readers, use the manufacturer's optical check and record the result.
RECORD
Example observation table
| Check | Reference | Measured | Error |
|---|---|---|---|
| Temperature, well A1 | 37.0 °C | 36.8 °C | −0.2 °C |
| Temperature, well A12 | 37.0 °C | 37.1 °C | +0.1 °C |
| Temperature, well D6 (centre) | 37.0 °C | 37.3 °C | +0.3 °C |
| Temperature, well H1 | 37.0 °C | 36.9 °C | −0.1 °C |
| Temperature, well H12 | 37.0 °C | 37.0 °C | 0.0 °C |
| OD at 405 nm, filter 1 | 0.500 | 0.503 | +0.6% |
| OD at 405 nm, filter 2 | 1.000 | 1.006 | +0.6% |
| OD at 405 nm, filter 3 | 2.000 | 2.012 | +0.6% |
CALCULATION
How to calculate the result
Temperature error = Measured − 37.0 °C; Photometric error (%) = (Measured OD − Certified OD) ÷ Certified OD × 100
- Highest temperature 37.3 °C and lowest 36.8 °C: all within 36–38 °C
- Filter 2: (1.006 − 1.000) ÷ 1.000 × 100 = +0.6%
- Filter 3: (2.012 − 2.000) ÷ 2.000 × 100 = +0.6%
- Within a typical tolerance of ±1% (or the filter certificate tolerance): Pass
ACCEPTANCE CRITERIA
Pass if
- All positions at 37 ± 1 °C (the incubation temperature in USP <85>).
- Absorbance within the tolerance given by the manufacturer or the filter certificate, often about ±1% plus a small fixed amount (e.g. 0.010 OD), as defined in your SOP.
IF IT FAILS
What to do
- Label the reader 'Not for use'.
- Have the manufacturer adjust or repair the heater or optics, then repeat the checks.
- Assess endotoxin results since the last passing check with QA.
In LimsPulse · Calibration Management
LimsPulse schedules this calibration, records the result against limits, and blocks the instrument everywhere if it fails or goes overdue.