Endotoxin (LAL) reader
An incubating photometer that holds LAL reactions at 37 °C and measures the change in absorbance or turbidity over time. Software turns the reaction onset time into an endotoxin concentration in EU/mL using a standard curve.
- Pharmaceutical
- Biotech
- Medical devices
- Dialysis and hospital pharmacy
- Research laboratories
How Endotoxin reader works
Endotoxin activates Factor C in the LAL, which starts a protease cascade. In chromogenic reagents the final enzyme cuts a synthetic substrate and releases yellow p-nitroaniline (read at 405 nm). In turbidimetric reagents the enzyme converts coagulogen to coagulin, which makes the solution turbid. The reader measures each well or tube over time; the onset time falls as endotoxin increases, and log onset time vs log concentration is linear.
The path of a sample
- 01
Prepare
Standards, samples, spiked samples and negative controls are made in LAL reagent water using pyrogen-free tips and tubes.
- 02
Pre-warm
The plate or tubes are pre-incubated at 37 °C in the reader.
- 03
Add LAL
Reconstituted LAL reagent is added to every well, quickly and in a fixed order.
- 04
Read kinetically
Absorbance (405 nm) or turbidity is read at short intervals while held at 37 °C.
- 05
Onset time
Software records the time each well reaches the set optical density.
- 06
Calculate
Onset times are converted to EU/mL via the log-log standard curve; recovery of spikes is calculated.
Main parts and what they do
Incubation block
Holds the microplate or tubes at 37 ± 1 °C.
Light source and filter (405 nm)
Provides light at the wavelength of p-nitroaniline for chromogenic tests.
Photodetectors
Measure transmitted light through each well or tube.
Plate carrier / tube wells
Position each reaction in the light path.
Temperature sensors
Monitor and control the block temperature.
Endotoxin software
Controls reading, builds the standard curve, calculates results and keeps an audit trail.
Terms every analyst should know
Endotoxin unit (EU)
Unit of endotoxin activity defined against the reference standard endotoxin (RSE). Control standard endotoxin (CSE) is calibrated against it.
Onset time
Time for the reaction to reach a set absorbance change. More endotoxin gives a faster reaction and a shorter onset time.
Lysate sensitivity (λ)
For kinetic methods, the lowest concentration on the standard curve; for gel-clot, the labelled sensitivity of the lysate (e.g. 0.03 EU/mL).
Positive product control (PPC)
Sample spiked with a known amount of endotoxin. Recovery shows that the sample does not inhibit or enhance the reaction.
Inhibition and enhancement
Product factors such as pH, chelators, proteins or high salt can slow or speed the reaction. Dilution up to the MVD is the usual remedy.
Temperature sensitivity
The enzyme cascade rate depends on temperature, so the reader must hold 37 ± 1 °C evenly across all wells.
Keep every Endotoxin reader in control: usage logs, calibration and maintenance schedules, and automatic blocking of overdue instruments.