How to choose an active microbial air sampler
An active microbial air sampler draws a defined air volume and deposits microorganisms onto a growth medium. This guide explains impactor versus impinger, the meaning of sampling flow rate and d50 value, and the requirements of ISO 14698 and EU-GMP Annex 1.
View air samplersImpactor or impinger - which principle fits?
Active microbial air samplers use a pump to draw a defined air volume. In an impactor the air stream passes through a sieve or slit nozzle at high velocity and strikes an agar medium, so particles and the microbes attached to them are deposited. In an impinger the air is instead led into a collection liquid that captures the microorganisms.
The impactor with a Petri dish or contact plate dominates routine monitoring in pharmaceutical production because the result is read directly as colony forming units (CFU). The impinger suits aerosols, viruses or cases where enrichment in liquid is preferred.
- Sieve impactor: many fine holes, even distribution across the plate.
- Slit impactor: rotating agar, allows time-resolved sampling.
- Impinger: air into liquid, ideal for viruses and soluble aerosols.
- Filtration: gelatine filters for sensitive or demanding organisms.
Flow rate and d50 - what matters physically?
Two figures decide how meaningful the result is: the sampling flow rate and the physical collection efficiency, expressed through the d50 value. The d50 is the aerodynamic particle diameter at which 50 percent of particles are collected. The smaller the d50, the more reliably small microbe-carrying particles are captured.
A high flow rate shortens the sampling time for 1 m³, but increases impact stress and drying of the agar. ISO 14698 requires that both the physical and the biological collection efficiency are known and documented, so that CFU results stay comparable.
What do ISO 14698 and Annex 1 require?
ISO 14698 describes biocontamination control in cleanrooms and requires that sampling devices are validated, calibrated and operated with a known efficiency. EU-GMP Annex 1 (2022 revision) calls for risk-based and, where possible, continuous microbial monitoring of the critical zones in aseptic processing.
- Regular calibration of the flow rate, ideally once a year.
- Documented physical and biological collection efficiency.
- Dischargeable, disinfectable stainless steel housing for sterile areas.
- Autoclavable sampling head to avoid cross contamination.
- Logging of volume, time and location for batch documentation.
Frequently asked questions
What does the d50 value mean on an air sampler?
The d50 is the aerodynamic particle diameter at which the device collects 50 percent of particles. A d50 below 1 µm shows that even small microbe-carrying particles are reliably captured.
What sample volume does Annex 1 require?
For assessing critical zones a sample volume of 1 m³ per reading is recommended, since only this gives statistically robust verification of the limit of fewer than 1 CFU per m³.
Impactor or impinger in a cleanroom?
For routine monitoring in GMP Grade A and B, impactors with agar plates are used. The impinger is chosen when viruses or soluble aerosols need to be collected in liquid.
How often must an active air sampler be calibrated?
The flow rate should be calibrated regularly, usually yearly, against a traceable standard. ISO 14698 requires documented calibration as a precondition for comparable CFU results.
Looking for the right air sampler?
We supply active impactor air samplers with a calibrated flow rate and documented d50 efficiency - suitable for monitoring under ISO 14698 and Annex 1.
Standard-compliant
Devices for monitoring under ISO 14698 and Annex 1.
Calibrated
Flow rate verified against a traceable standard.
Efficiency proven
Physical and biological collection efficiency in the datasheet.
Expert advice
Cleanroom specialists help with the selection.