The Requirements for Sample Dispersion in Static Image Analysis

The Requirements for Sample Dispersion in Static Image Analysis

 

Static image particle analyzers obtain particle morphology, size distribution, and quantity statistics by capturing static microscopic images of samples. The accuracy and repeatability of their analysis results are highly dependent on sample dispersion quality. Improper dispersion (e.g., agglomeration, overlap, sedimentation) directly leads to misjudgment of particle size, distortion of morphology, or deviation in counting. Therefore, there are clear and strict requirements for sample dispersion, which can be detailed from the following 6 core dimensions: 

 

Core Requirement 1: No/Little Agglomeration, Ensuring "Single-Particle State"  

 

Static image analyzers need to identify the contour and characteristics of individual particles. Agglomeration (particle adhesion due to van der Waals forces, electrostatic forces, or hydrogen bonds) is the most critical interfering factor. Thus, the requirements are:

 

• Ideal State: Over 95% of particles in the sample exist in an "independent single-particle" form, with no physical adhesion between two or more particles (especially preventing small particles from adhering to the surface of large particles).

 

• Special Scenarios: For samples with strong agglomeration tendencies (e.g., nanoparticles, ultrafine powders), dispersion methods (such as ultrasound or adding dispersants) must be used to "deagglomerate" agglomerates into primary particles. Alternatively, "agglomerate size" should be clearly marked in the report (to be distinguished from primary particles).  

 

• Counterexample: If a bulk agglomerate is mistakenly identified as a "single large particle," the size result will be excessively large; small particles adhering to large particles will distort the calculation of morphological characteristics.

 

Core Requirement 2: No Overlap/No Occlusion, Ensuring Complete Particle Contours 

 

Static image analyzers recognize particle edges and contours through image algorithms. If particles overlap or are occluded in the field of view, the algorithm cannot distinguish individual particles. Therefore, the requirements are: 

 

• Spatial Distribution: Particles should be evenly arranged on the glass slide. The edges of any two particles must not intersect or overlap.

 

• Density Control: The "surface density" of the sample on the glass slide must be moderate—neither too dense (causing overlap) nor too sparse (resulting in insufficient statistical sample size and unrepresentative results). Generally, it is recommended to control the number of particles per field of view between 50 and 200 (adjusted according to particle size; more small particles can be allowed).

 

Core Requirement 3: Dispersion Uniformity, Avoiding Local Concentration Deviations 

 

The analysis results of static image analyzers are based on "random sampling." If the sample is unevenly dispersed (local over-density or local sparsity), sampling bias will occur. Thus, the requirements are: 

 

• Spatial Uniformity: Particles should be evenly distributed within the observation area (e.g., the entire analysis area of a glass slide, the optical path of a sample cell), with no "local accumulation" or "local blank areas." 

 

• Temporal Stability: For liquid-dispersed samples, particle sedimentation (e.g., rapid sinking of large particles) or floating (e.g., light particles) during analysis must be avoided. The dispersion state should remain stable during image acquisition (usually a few seconds to several minutes), with no concentration stratification. 

 

Core Requirement 4: Compatibility of Dispersion Medium, No Interference 

 

The dispersion medium (e.g., air, water, ethanol, organic solvents) must be compatible with the sample and the instrument to avoid secondary interference with the analysis. The requirements are: 

 

• No Reaction with Samples: The medium must not undergo chemical reactions with the sample (e.g., dissolution, oxidation, hydrolysis) to prevent changes in particle size or morphology (e.g., water-soluble particles cannot use water as the dispersion medium; ethanol or oil-based media should be selected instead).

 

• Optical Transparency/Low Interference: The medium must have good optical transparency (especially for transmission-type static image analyzers), with no color or impurities (e.g., bubbles, dust) to avoid blocking particles. 

 

Core Requirement 5: Dispersion Stability, Ensuring Consistency During Analysis 

 

Image acquisition by static image analyzers usually takes a certain amount of time (e.g., multi-field scanning). Therefore, the dispersion state must remain stable throughout the analysis cycle: 

 

• No Sedimentation/Floating: For liquid dispersion systems, the viscosity of the medium (e.g., adding glycerol), the density difference of particles (e.g., selecting a medium with a density close to that of the particles), or gentle stirring (to avoid disturbing particles) can be adjusted to prevent particle sedimentation (large particles) or floating (light particles) during acquisition. 

 

• No Re-agglomeration: For samples that tend to re-agglomerate after dispersion (e.g., nanoparticles), analysis should be performed immediately after dispersion, or stabilizers (e.g., surfactants) can be added to inhibit agglomeration, ensuring consistent particle state throughout the analysis process. 

 

Core Requirement 6: Adapting to Particle Characteristics, Customizing Dispersion Schemes 

 

Different types of particles (in terms of size, material, morphology, and surface properties) have different dispersion requirements, requiring targeted adjustments: 

 

• Size Differences: 

  - Micron-scale particles: Can usually be dispersed by mechanical stirring (e.g., magnetic stirring) or ultrasound (low power, to avoid breaking particles); 

  - Nanoparticles: Require high-power ultrasound + dispersants (e.g., sodium dodecyl sulfate, SDS), and the ultrasound duration must be controlled (to avoid overheating causing particle agglomeration or morphological damage). 

 

• Material Differences: 

  - Inorganic particles (e.g., silica, metal powders): If hydrophilic, water + dispersant can be selected; if hydrophobic, organic solvents such as ethanol and toluene are suitable; 

  - Organic particles (e.g., polymer microspheres, biological particles): The medium must not dissolve or damage the particle structure (e.g., physiological saline should be used for dispersing biological particles). 

 

• Morphological Differences: 

  - Fragile particles (e.g., acicular, flaky particles): High-intensity ultrasound or mechanical grinding should be avoided to prevent particle breakage and morphological distortion; 

  - Viscous particles (e.g., resin particles): The dosage of dispersants should be increased or low-viscosity media selected to reduce particle adhesion. 

 

Summary

 

"Golden Standard" for Sample Dispersion in Static Image Analyzers 

 

The ultimate goal is to achieve a dispersion state that is "single-particle, non-overlapping, uniform, stable, and interference-free". Specifically, it is necessary to combine sample characteristics (size, material, morphology), instrument type (transmission/reflection), and analysis requirements (size accuracy, morphological resolution) to design a combined scheme of "dispersant selection + dispersion method (ultrasound/stirring) " This ensures that the image algorithm can accurately identify and analyze each particle, thereby obtaining reliable results.