Causes and Countermeasures for Strange Data in Laser Diffraction and Scattering Particle Size Analyzers

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This time, I will talk about the causes of “strange data” that often occur in laser diffraction and scattering particle size analyzers and how to address them.

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Case 1: Abnormal Peak Sticking to the Measurement Upper Limit

If an abnormal peak sticks to the measurement upper limit, the following causes and countermeasures are possible.

Optical Axis Misalignment

This is caused when the optical axis of the device is misaligned, causing transmitted light to enter a detector other than the intended one. Re-adjusting the optical axis is necessary as a countermeasure.

“Hazy” Due to Temperature Variations in Organic Solvents

In particular, for organic solvents, temperature variations cause light scattering and create abnormal peaks. As a countermeasure, it is important to let the dispersant acclimate to the measurement room temperature several hours before measurement.

Case 2: Abnormal Peak Above 100 μm

If abnormal peaks occur above 100 μm, the following causes and countermeasures are possible.

Bubble Entrapment

Bubbles can be suppressed by changing stirring speed and the type or concentration of surfactant.

Aggregates

Abnormal peaks can occur due to aggregation of large particles. Increasing the strength or duration of ultrasonic dispersion, or applying ultrasound in pre-treatment can reduce the effect of aggregates.

Case 3: Two or Three Peaks in the Submicron to Tens of Microns Range

If two or three peaks appear in the submicron to tens of microns range, the following causes are possible.

Irregularities in Mie Scattering Theoretical Values

When the distribution width expands, the peaks can become irregular. As a countermeasure, it’s important to change calculation conditions or check with an image-type particle size distribution analyzer.

Sample Itself Contains Multiple Peaks

When the sample itself contains multiple particle sizes, multiple peaks may appear.

Case 4: Large Peak in Submicron Range When Measuring Samples Over 1 μm

If a large peak appears in the submicron range when measuring samples over 1 μm, the following causes are possible.

“Stray Light” to the Backward Detector from the Main Sample

This is caused as entering light from the backward makes the device mistakenly detect small particles.

Fundamental Limitations

Scattered light from nanoparticles is weak, and scattered light from particles over 1 μm is strong, making it difficult to distinguish the presence of nanoparticles. As a countermeasure, increasing the complex refractive index (absorption rate) through calculations may help.

Case 5: Particle Size Increases During Measurement, and Scattered Light Weakens (Transmission Increases)

If the particle size increases during measurement, and scattered light weakens, the following causes are possible.

Sample Dissolution

This is caused when smaller particles in the sample dissolve first, shifting the particle size distribution larger. Using a dispersant that does not dissolve the sample is effective as a countermeasure.

Progress of Aggregation

This is caused when particles aggregate during stirring or circulation. As a countermeasure, consider changing the dispersant or using a high-concentration compatible cell to measure in the original solution.

These are the explanations for the causes and countermeasures for “strange data” that often occur in laser diffraction and scattering particle size analyzers. When using the device, it is important to keep these causes and countermeasures in mind to obtain accurate measurement results.

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