Particle counters: how can particle concentration in air and liquids be monitored?

Essential in cleanrooms and quality control, particle counters measure, in real time, the concentration and particle size distribution in the air or in liquids. They safeguard compliance with ISO 14644, GMP Annex 1 and the pharmacopoeias (USP <788>, Ph. Eur. 2.9.19). Handheld for audits, fixed for continuous monitoring, or dedicated to injectable solutions, they inform your decisions: batch release, environmental qualification, HACCP diagnostics, process validation. With traceability (21 CFR Part 11) and ISO 21501 calibration, you manage risk with confidence.

What are the different types of particle counters?

Three main families cover most needs. Airborne particle counters by laser light scattering/obscuration (OPC) typically measure 0.3 to 10 µm, with flow rates from 2.83 L/min (0.1 CFM) to 28.3 L/min (1 CFM). In portable form, they handle mapping and qualification (ISO 14644). In fixed/remote setups, they provide continuous monitoring and BMS/EMS integration. For ultrafine particles (<0.1 µm), CPC (condensation particle counters) detect down to ~10 nm for R&D and microelectronics. For liquids, light-obscuration (LO) particle counters meet requirements for suspended particles in injectables and process waters (USP/Ph. Eur.).

Key selection criteria: sensitivity (0.1/0.2/0.3 µm threshold), flow rate (qualification speed), number of channels and resolution, ISO 21501 accuracy, data management (audit trail, Part 11), cleanroom-compatible materials, battery life, and accessories (isokinetic probes, zero filters, T/RH/?P probes). For liquids: sample volume, degassing/anti-bubble capability, allowable viscosity and pressure, and rinsing to avoid sample carryover.

Comparative table

Type	Principle	Applications
Air OPC (portable/fixed)	Laser light scattering/obscuration	ISO 14644, GMP, cleanroom qualification & monitoring
CPC (ultrafine)	Condensation on a nucleus, then optical counting	Nanoparticles, microelectronics, aerosol R&D
Liquids (LO)	Light obscuration	USP <788>, Ph. Eur., water/injectable preparations, oils

In which fields are particle counters used?

• Pharma/biotech : ISO 14644 qualification, environmental monitoring compliant with GMP Annex 1, checks in Grade A/B areas, sterile batch release (air) and particulate testing in liquids.
• Medical devices : control of particulate biocontamination on assembly lines and in cleanrooms, real-time trending and alarms.
• Microelectronics/optics : strict particle monitoring (down to nanoparticles with CPC) to minimise defects and yield loss.
• Food/cosmetics : validation of controlled-environment areas, HACCP assessments, packaging inspection and aseptic filling.
• Environment & HVAC : indoor air quality audits, filtration optimisation, qualification of laminar flow units and cabinets.
• Chemistry & process : monitoring of fluids (water, solvents, oils) to protect equipment and ensure product quality.

The different types of particle counters available

Particle counter

Frequently asked questions about particle counters

What’s the difference between OPC and CPC air particle counters?
An OPC measures 0.3–10 µm via laser light scattering. A CPC extends detection down to ultrafine particles (~10 nm) by condensation, valuable in R&D and microelectronics.

How do I choose the sampling flow rate?
1 CFM (28.3 L/min) speeds up ISO 14644 qualifications. Lower flows suit spot checks or sensitive areas.

Which compliance standards should I check?
ISO 14644 for cleanrooms, ISO 21501 for calibration, GMP Annex 1 for monitoring, USP <788>/Ph. Eur. 2.9.19 for liquids.

Do CPCs use a working fluid?
Yes—often butanol. Handle it safely (ventilation, storage) and follow maintenance of the saturator and filters.

How can I avoid false positives in liquids?
Degas the sample, avoid bubbles, rinse the cell, stabilise the temperature and observe the prescribed volumes.

Which accessories are useful for air measurements?
Isokinetic probes, impactors, zero-count filters, T/RH/?P probes, tripods and anti-static tubing.

Is data management secure?
Favour audit trails, user management, electronic signatures and secure export to comply with 21 CFR Part 11.