🔬 Particle Size Analysis — Laser Diffraction
In short
Determination of particle size distribution (0. 1 µm – 3 mm) in powders, suspensions, emulsions and aerosols by laser diffraction method. The test is performed according to PN-EN ISO 13320:2020; Measurement range: 0.01–3 500 µm (depending on model and configuration). The procedure comprises 10 steps (about 40–42 min in total); it is used for: Quality control of cement, lime, gypsum (construction industry), Analysis of active substance particle size in pharmacy (API, granules), Control of metal powders for 3D printing (SLM/SLS).
At a glance
- Standard: PN-EN ISO 13320:2020
- Category: Physicochemistry
- Procedure steps: 10
- Total time of stages: 40 min–42 min
- Measurement range: 0.01–3 500 µm (depending on model and configuration)
- Distribution indices: D10, D50 (median), D90, D[4,3], D[3,2], SPAN
- Repeatability: CV < 1% (D50) for homogeneous samples
Overview
Particle size analysis by laser diffraction method is one of the most widely used techniques for determining particle size distribution in pharmaceutical, chemical, construction, food, cosmetic and materials industries. Standard PN-EN ISO 13320:2020 defines method principles, apparatus requirements and measurement procedure.
The method is used in the particle size range from approx. 0.1 µm to 3 mm (and with extensions — below 0.1 µm and above 3 mm). Sample in suspension (wet dispersion) or aerosol (dry dispersion) form passes through monochromatic laser light beam. Particles scatter light at angles depending on their size — smaller particles scatter at larger angles. Angular distribution of scattered light is recorded by photodetector array and converted to particle size distribution.
Calculations are based on Mie theory (for spherical particles) or Fraunhofer approximation (for particles >> wavelength). Results are expressed as volume distribution with indices D10, D50 (median) and D90, as well as SPAN parameter and De Brouckere mean (D[4,3]).
Leading laser analyzer manufacturers are: Malvern Panalytical (Mastersizer 3000), Horiba (LA-960V2), Beckman Coulter (LS 13 320), Sympatec (HELOS), Fritsch (Analysette 22). Equipment cost 80 000–600 000 PLN, measurement time 1–5 minutes.
Method principle
Monochromatic laser beam (He-Ne 633 nm or diode 470 nm) illuminates sample dispersed in medium (liquid or air). Particles scatter light — scattering angle is inversely proportional to particle size (small particles → large angles). Angular intensity distribution of scattered light is measured by concentric photodetector array (detectors at angles 0.01°–135°). Based on measured diffraction pattern, algorithm based on Mie theory (requiring knowledge of sample and medium refractive index) calculates particle size distribution (volume).
Applications
- Quality control of cement, lime, gypsum (construction industry)
- Analysis of active substance particle size in pharmacy (API, granules)
- Control of metal powders for 3D printing (SLM/SLS)
- Analysis of emulsions and suspensions in cosmetic and food industries
- Control of pigments and paints (size distribution affects color and coverage)
- Analysis of soils and sediments in geology and environmental protection
- Control of aerosols and pharmaceutical inhalers (MDI, DPI)
- Testing of ceramic and refractory materials
Key parameters
| Parameter | Value |
|---|---|
| Measurement range | 0.01–3 500 µm (depending on model and configuration) |
| Distribution indices | D10, D50 (median), D90, D[4,3], D[3,2], SPAN |
| Repeatability | CV < 1% (D50) for homogeneous samples |
| Optical model | Mie theory (requires refractive index n and k) or Fraunhofer |
| Measurement time | 1–5 min (including dispersion) |
| Dispersion | Wet (water, isopropanol, hexane) or dry (compressed air) |
Standard
- Standard number
- PN-EN ISO 13320:2020
- Title (PL)
- Analiza wielkości cząstek — Metody dyfrakcji laserowej
- Title (EN)
- Particle size analysis — Laser diffraction methods
Step-by-step procedure
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Instrument preparation
Turn on analyzer and laser min. 30 min before measurement. Launch software, zero optical system.
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Background measurement
Fill cell with dispersion medium (without sample). Perform background measurement. Background absorbance < 0.5%.
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Parameter selection
Enter sample refractive index (n) and absorption (k) into Mie model. Select medium, pump speed, ultrasonic power.
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Sample dosing
Add sample to medium in drops / spatula, monitoring obscuration. Target 5–20% obscuration.
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Dispersion
Turn on circulation pump and ultrasonics (wet) or air stream (dry). Disperse 30–60 s.
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Measurement
Start measurement (usually 3–5 scans, averaging). One scan time: 10–20 s. Check repeatability between scans.
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Result verification
Check Mie model residuals (< 1%), obscuration, D50 repeatability (CV < 3% between measurements). Repeat measurement 3× on independent weighings.
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Results analysis
Read D10, D50, D90, SPAN = (D90-D10)/D50. Compare with product specification requirements.
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Cleaning
Rinse cell with medium, then purified water (3×). For poorly soluble samples — isopropanol or acetone.
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Quality control
At least once daily measure certified standard (glass beads). D50 in range ±3% of certified value.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Laser diffraction analyzer | Malvern Mastersizer 3000, Horiba LA-960V2, Beckman Coulter LS 13 320 | 150 000–600 000 PLN |
| Wet dispersion module | Malvern Hydro MV / Hydro SV, Horiba PowderJet | Included or 30 000–80 000 PLN |
| Dry dispersion module | Malvern Aero S, Horiba PowderJet Dry | 50 000–100 000 PLN |
| Ultrasonic bath | Built into dispersion module or external (Bandelin, Elma) | 3 000–8 000 PLN |
| Particle size standard | Malvern QAS3001B (15–150 µm glass beads), NIST SRM 1003c | 2 000–5 000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Purified water | — | Dispersion medium for hydrophilic samples, degassed, filtered 0.2 µm |
| Isopropanol | 67-63-0 | Dispersion medium for water-sensitive samples (cement, metal powders) |
| Surfactant (Tween 80 / Triton X-100) | 9005-65-6 | Prevents agglomeration — added to wet medium (0.1–0.5%) |
| Spherical standards (glass beads) | — | Certified glass microspheres with known distribution — verification of instrument calibration |
Health and safety (OHS)
- Class 1 laser (enclosed in instrument) — do not open housing during operation
- Isopropanol — flammable, ventilation, do not use near fire
- Powders — avoid inhalation, use dust mask when dosing
- Compressed air (dry dispersion) — noise, protect hearing
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 13320:2020 — “Particle size analysis — Laser diffraction methods”.
How does this method work?
Monochromatic laser beam (He-Ne 633 nm or diode 470 nm) illuminates sample dispersed in medium (liquid or air). Particles scatter light — scattering angle is inversely proportional to particle size (small particles → large angles).
What is the measuring range and accuracy?
Measurement range: 0.01–3 500 µm (depending on model and configuration); Distribution indices: D10, D50 (median), D90, D[4,3], D[3,2], SPAN; Repeatability: CV < 1% (D50) for homogeneous samples; Optical model: Mie theory (requires refractive index n and k) or Fraunhofer.
How long does the test take?
The times given for the individual stages add up to approximately 40 min–42 min. The procedure comprises 10 steps.
What equipment is required?
Laser diffraction analyzer, Wet dispersion module, Dry dispersion module, Ultrasonic bath, Particle size standard. Indicative cost of the core instrument (Laser diffraction analyzer): 150 000–600 000 PLN.
Where is this test used?
Quality control of cement, lime, gypsum (construction industry); Analysis of active substance particle size in pharmacy (API, granules); Control of metal powders for 3D printing (SLM/SLS); Analysis of emulsions and suspensions in cosmetic and food industries; Control of pigments and paints (size distribution affects color and coverage); Analysis of soils and sediments in geology and environmental protection; Control of aerosols and pharmaceutical inhalers (MDI, DPI); Testing of ceramic and refractory materials.
What safety precautions apply?
Class 1 laser (enclosed in instrument) — do not open housing during operation; Isopropanol — flammable, ventilation, do not use near fire; Powders — avoid inhalation, use dust mask when dosing; Compressed air (dry dispersion) — noise, protect hearing.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 13320.