How is particle size measured? 6 methods for industrial powder analysis
Particle size measurement in industrial powder analysis — definition: Particle size determination is the quantitative analysis of grain size distribution (D10, D50, D90 in µm) in bulk powders via laser diffraction, sieve series, dynamic light scattering (DLS) or image analysis — a critical process variable for bulk density, flowability (Carr Index), mixing homogeneity and OEB containment risk in pharma, food and chemistry.
Key points
- Method 1 — Laser diffraction (ISO 13320): fast, reproducible, D50 range 0.1–3,500 µm — standard in GMP Annex 1 (2022) validation
- Method 2 — Sieve series (ISO 3310): simple, low-cost, suitable for D50 >63 µm — reference method for food and bulk chemicals
- Method 3 — Dynamic light scattering (DLS/PCS): nanosuspensions 0.001–10 µm — pharma nanomedicine and API nanoformulations
- Standards: ISO 13320 (laser diffraction), ISO 9276 (statistical representation), USP <429> (light diffraction), Ph.Eur. 2.9.31 (particle size analysis)
- Process impact: a 10% shift in D50 can change flowability (Carr Index) by 15–25 points — direct effect on dosing accuracy of the HECHT LAS-EC screw
Reliable particle size determination is the foundation for optimised powder processing — discover our powder processing solutions, learn how we support pharmaceutical powder characterisation, or test your product at our Test & Trial Centre in Pörnbach.
Particle size is measured using 6 main techniques: laser diffraction (0.02-2000 µm), sieve analysis (45 µm-125 mm), image analysis, dynamic light scattering (DLS), sedimentation and Coulter counter. The choice depends on the measurement range, product density and industry requirement (pharma per USP <429>, food per ISO 13320). HECHT analyses particle size in the Barcelona lab and validates containment impact in Delft.
Why this is essential
Particle size directly affects: dissolution rate (pharma), reactivity (chemistry), electrochemical performance (battery), texture (food) and dust behaviour during transport. A uniform distribution (D90/D10 ratio < 3) prevents segregation during pneumatic powder transport and guarantees reproducible product quality.
The 6 main methods compared
| Method | Range (µm) | Standard | Best application |
|---|---|---|---|
| Laser diffraction | 0.02 – 2000 | ISO 13320, USP <429> | Pharma, chemistry, battery |
| Sieve analysis | 45 – 125,000 | ASTM E11, ISO 3310 | Bulk food, granulate |
| Image analysis | 1 – 30,000 | ISO 13322 | Shape analysis + size |
| DLS | 0.001 – 10 | ISO 22412 | Nanopowders, suspensions |
| Sedimentation | 0.1 – 100 | ISO 13317 | Pigments, clay |
| Coulter counter | 0.4 – 1600 | ISO 13319 | Cells, microbubbles |
Step-by-step plan for particle analysis
Sample preparation
Sample drawn per ISO 14488 (gold standard) or ASTM E1402. Representativeness is critical — incorrect sampling causes 80% of all measurement errors.
Selecting the measurement method
Based on expected D50, product chemistry and target standard. For API powder with D50 between 5 and 100 µm, laser diffraction is standard.
Data acquisition
At least 3 repeats per sample. Coefficient of Variation (CoV) on D50 < 3% for pharma, < 5% for chemistry.
Analysis and interpretation
Distribution reported as D10, D50 (median), D90 and span [(D90-D10)/D50]. Span < 1.5 = narrow, > 3 = broad.
Compliance by industry
- Pharma: USP <429> + EP 2.9.31 + ICH Q6A — D90 below maximum spec
- Battery: GB/T 19077 + ASTM B822 — for cathode materials
- Food: ISO 13320 + EHEDG protocol — texture validation
- Chemistry: ISO 13320 + REACH dossier — for REACH registration
- Containment: SMEPAC measurement validates OEL for a specific particle size distribution
Hecht's approach: particle size and containment
In powder processing, particle size and containment requirements go hand in hand: finer powder = higher OEL risk = stricter OEB level required. Our containment experts calculate the right containment strategy based on your particle distribution. Specific products:
- HECHT EWI for OEB 5+ powders with D50 < 5 µm
- ProClean Conveyor (PCC) with D50-range filters for pharmaceutical APIs
- FDS Filling-Discharge-System for battery raw materials with tight spec
The Test & Trial Centre in Pörnbach connects particle sizing to containment performance via SMEPAC validation.
Case study: cathode powder for a battery manufacturer
A battery OEM had a D50 spec of 8±0.5 µm for an NMC cathode powder, with an OEB 3 requirement. HECHT tested the powder via laser diffraction (Mastersizer 3000) in the Barcelona lab, validated the transport behaviour in a PCC system in Delft, and measured the actual OEL via SMEPAC. Result: 0.9 µg/m³ (within the OEB 3 spec of 1-10 µg/m³). The system went into production 6 weeks later.
Frequently asked questions
What is the difference between D10, D50 and D90?
D50 is the median particle size: 50% of particles are smaller. D10 means 10% is smaller, D90 means 90% is smaller. For pharmaceutical APIs, D90 is often specified to control the upper end. The span value [(D90−D10)/D50] indicates the width of the distribution.
Which method is most accurate for powder analysis?
Laser diffraction per ISO 13320 is the global standard for powders between 0.02 and 2000 µm. For nanopowders < 1 µm, dynamic light scattering (DLS) is more accurate. For product shape analysis alongside size: dynamic image analysis (DIA).
How much sample do I need for a particle size measurement?
For laser diffraction: 50–500 mg powder. For sieve analysis: 100–500 g. For representativeness, the sample must contain at least 1,000× the largest particle size per ISO 14488.
How does particle size affect the containment level?
Fine particles (D50 < 10 µm) stay airborne longer and produce higher OEL values. A D50 of 5 µm typically requires OEB 4 containment, a D50 of 50 µm is sufficient with OEB 2-3. SMEPAC measurement at the Test & Trial Centre validates the actual OEL.
What does a particle size measurement cost?
External laboratories charge €150-€450 per laser diffraction measurement (triplicate with report). HECHT offers particle sizing as part of engineering projects and during containment validation.
Conclusion
Particle size measurement directly determines which containment level, transport system and compliance standard apply to your powder. HECHT Technology combines particle sizing (Mastersizer 3000) with SMEPAC containment validation and pneumatic transport engineering. Call 085 - 06 00 670 or email info@hecht-technology.nl.
Author: Joost van Velzen, Managing Director Hecht Technology B.V.
FAQ — Measuring particle size: 6 methods for industrial powder analysis
Which particle size determination method is most accurate for pharmaceutical powders?
Laser diffraction (ISO 13320) is the GMP standard for pharma: reproducible, fast (30 sec/measurement), broad measurement range (0.1–3,500 µm) and validatable per USP <429> and Ph.Eur. 2.9.31. For nano-APIs (<1 µm), dynamic light scattering (DLS) is the complement. Sieve series remains the reference method for coarse granulate >63 µm.
How does particle size affect the flowability and dosing accuracy of powders?
Smaller particles (D50 <50 µm) increase cohesion (Carr Index >25) and reduce flowability — this decreases dosing accuracy on HECHT LAS-EC screws by 10–20%. Larger particles (D50 >200 µm) improve flowability but increase segregation risk in mixing systems. Particle size control is therefore critical for GMP-compliant dosing.
Which particle size determination is required for ATEX classification of powders?
For ATEX assessment, the median particle size D50 <500 µm and dust explosivity index (Kst value) are decisive. Powders with D50 <500 µm and Kst >200 bar·m/s fall into ATEX class St 2/3 — ATEX Zone 20/21 measures mandatory. HECHT advises on explosivity analysis and supplies ATEX-compliant processing solutions.
Author: Joost van Velzen, Managing Director Hecht Technology B.V.