FAQ – Frequently Asked Questions

Single Particle Extinction and Scattering (SPES) is a high-resolution analysis technique that characterises a sample particle by particle. Unlike “ensemble” methods (such as Laser Diffraction or DLS) that provide an average statistical value, SPES measures each individual particle passing through the laser beam. Its unique advantage lies in the simultaneous measurement of three independent optical parameters (extinction, forward scattering, side scattering) for every single event.

Traditional methods such as DLS, SLS, and SPOS typically measure only one parameter such as light scattering or light extinction, which primarily relates to particle size. By measuring several scattering parameters simultaneously, SPES technologies discriminate particles based on their effective refractive index and internal structure. This allows you to distinguish between particles of the same size but different materials (e.g., silica vs. polystyrene).

This is precisely a core strength of SPES. Because it is sensitive to optical properties, SPES can differentiate and characterise heterogeneous populations. In a mixture of materials, SPES generates a two-dimensional histogram where different populations appear as distinct clusters, allowing for the precise classification and calculation of the relative concentration of each type of particle based on its optical properties.

SPES can identify, count, and characterise individual aggregates or contaminants even at extremely low concentrations, well suited to stability and purity testing. Being a single-particle technology, SPES does not suffer from the “masking effect” common in statistical techniques where small particles overshadow larger ones.

Yes. As a single-particle counting system supported by a high-precision automatic syringe pump, Classizer™ ONE provides the absolute numerical concentration (particles/mL) of each particle population identified in a mixture. This is critical in R&D and QC where weight-based distribution is insufficient for quality control.

Thanks to the sample manager LMS™, the sample autodilutor LAD™, and the autosampler LAS™, the process is almost entirely automated. The system can handle concentrated samples and dilute them in real-time to the optimal counting condition. This eliminates human error and ensures maximum repeatability of the measurement.

Many extinction-based systems fail if the particle’s refractive index is close to that of the liquid. SPES overcomes this by exploiting the interference between the forward scattering and the transmitted beam, enabling it to detect differences in refractive index between the object and the medium down to 0.001 (oil gels dispersed in the oil itself, for example). Even if a particle is nearly transparent, its scattering signature remains detectable, ensuring accurate counting where other systems see nothing.

Yes. Organic and inorganic materials have different scattering responses. By mapping particles based on multiple independent optical parameters, SPES differentiates between these two or more populations, a task that is impossible for traditional diameter-only analysis.

DLS provides a mean diameter and often fails to detect the early formation of aggregates because it is an ensemble technique. SPES analyses every single particle passing through the measurement volume. While a minimum concentration is required for statistical significance (ideally at least 10⁴ particles/mL), Classizer™ ONE detects and counts these aggregates long before they impact the average data of a DLS measurement, allowing you to predict product instability at a much earlier stage.

The accuracy of concentration values (particles/mL) depends on the precision of the analysed volume. Our automatic LMS™ liquid sample manager is based on a high quality syringe pump which eliminates the flow fluctuations typical of peristaltic or diaphragm pumps. Its usage also considerably speeds up the measurements, as it communicates with the Classizer™ ONE allowing the smoothest and fastest measurement possible with minimal sample consumption. Furthermore, the LAD™ single point autodilutor ensures the sample is never too concentrated (avoiding coincidence errors) nor too diluted, preserving the integrity of fragile aggregates.

Yes. By tracking both numerical concentration and optical fingerprints, SPES allows you to monitor not just size increase, but also changes in the nature of the population (e.g., the transition from amorphous to crystalline states). The Classizer™ ONE can track these changes with a resolution down to 1 second, or can be easily set up with the LMS™ to perform longer runs of even days with measurements at specified intervals, like 1 hour.

In many light-scattering or obscuration systems, an air bubble is mistakenly counted as a solid particle. SPES identifies the unique “optical signature” of a bubble versus a solid contaminant — more precisely SPES sees that the bubble has a lower refractive index than water. This eliminates false positives and ensures your purity data reflects reality.

Yes, as water impurities have a lower refractive index than the oil they are typically immersed in. SPES also sees the sign of the differences between the refractive index of the oil and the particles and can thus confirm the presence (or absence) of water impurities with an extremely high degree of accuracy. In an oil sample, this allows to separate water impurities from other particles – like wear particles in lubricating oils.

Emulsions degrade through coalescence or flocculation. While traditional systems only see an increase in “mean diameter,” Classizer™ ONE detects changes in numerical concentration and optical properties distribution. We can spot the emergence of larger droplets with lower refractive index long before the emulsion visibly separates.

Yes, within the micron/sub-micron range. Bacteria exhibit specific scattering characteristics compared to inorganic debris. SPES sensitivity allows for the identification of population anomalies which indicate bacterial growth, serving as an early-warning system for process safety.

In microencapsulation, it is critical that the “shell” is intact and no active ingredient leaks out. SPES distinguishes between intact capsules and broken or poorly formed ones by analysing differences in effective refractive index and internal optical structure, providing a level of QC that laser diffraction cannot match.

Certainly. The combination of our high-speed sensors and precise flow management allows Classizer™ ONE and SPES technologies to be integrated directly into a continuous flow system. The Classizer™ ONE has a time resolution of 1 second, allowing real-time monitoring with extreme precision, either on-line or at-line with the addition of an autodilutor.

Principal Component Analysis (PCA) is an advanced statistical method used to manage the rich data generated by SPES. Instead of looking at simple 2D plots, PCA automatically clusters particles based on all their optical properties. This identifies different particle “families” objectively, making the interpretation of complex mixtures intuitive even for non-experts.

Yes. As an Italian engineering firm, we excel in providing tailored solutions. We have full control on all engineering aspects of our instruments and can thus provide a complete customisation: from the dimensions of the cuvette’s flow channel to the wetted parts (tubing and connectors) to ensure full chemical compatibility, from the software to the final reports.

Choosing EOS Instruments means investing in metrological traceability, high-quality materials, and direct access to the inventors and designers of the SPES technologies. We offer personalised technical support and the flexibility to adapt our systems to your laboratory or industrial process—a level of responsiveness and long-term reliability that mass-market retailers cannot provide.