From EntegrisReviewed by Danielle Ellis, B.Sc.Apr 29 2026
In this interview, AZoM speaks with Mark Bumiller, Technology Manager for the AMH Instrumentation Division at Entegris, about particle sizing using Single Particle Optical Sizing (SPOS) technology. He explains how liquid particle counting and tail-of-distribution analysis solve complex challenges across additive manufacturing, inkjet inks, pharmaceuticals, and contamination control applications.
This interview summarizes the recent webinar presented by Mark - you can watch the webinar here.
Can you please introduce yourself and your role at Entegris?
My name is Mark Bumiller, and I am the Technology Manager for the AMH Instrumentation Division at Entegris. I have worked in particle size analysis for over 40 years. Throughout my career, I have focused on helping customers select and apply the correct particle sizing techniques for their specific needs.
At Entegris, I work with Single Particle Optical Sizing technology, often referred to as SPOS. Our systems are used both externally by customers and internally within Entegris to control contamination and optimize product performance in industries such as semiconductors, pharmaceuticals, and specialty chemicals.
What is Single Particle Optical Sizing, and how does it differ from other particle sizing methods?
Single Particle Optical Sizing is a liquid-based particle sizing technique that measures particles one at a time as they pass through a laser beam. Unlike other liquid particle counters that rely on either extinction or scattering detection, our sensor combines both. This dual detection expands the dynamic range and improves measurement capability.
Each particle generates a pulse as it interacts with the laser. That pulse is converted into an equivalent spherical diameter using a calibration curve. Because we measure each particle individually and use 1,024 size channels, the result is extremely high resolution and model-independent.
The technology covers a broad dynamic range from approximately 0.5 to 400 microns, which allows it to address both contamination measurements and full particle size distribution analysis.
How can particle sizing be performed using both number and volume distributions?
The primary measurement in SPOS is the number distribution because particles are counted individually. From this, we can calculate the volume distribution.
The number distribution emphasizes smaller particles because each particle is weighted equally. The volume distribution, however, accentuates larger particles since volume scales with the cube of diameter.
Image Credit: Corona Borealis Studio/Shutterstock.com
This distinction is critical. In some applications, such as powder flow analysis, fines play a significant role, making number distributions highly valuable. In other applications, such as emulsion stability, the volume percent of larger particles is more relevant. The ability to evaluate both distributions provides deeper insight into product behavior.
Why is repeatability so important in particle sizing measurements?
Repeatability is fundamental. If the measurement is not reproducible, it cannot be trusted.
When dispersing powders in liquids, for example, we evaluate repeatability by examining overlays of multiple runs and calculating the coefficient of variation. In our work, a coefficient of variation below approximately 5 percent indicates acceptable reproducibility.
This confirms that sample preparation was performed correctly and that the data can be used confidently for process optimization or quality control decisions.
How does SPOS technology improve analysis of tails of particle size distributions?
Many techniques perform well in the central portion of a distribution but struggle at the extremes. With SPOS, we can measure well beyond the D99 region of a distribution.
In laser diffraction, I typically would not recommend relying heavily on data beyond the D90. In contrast, SPOS excels at analyzing both fine and coarse tails. This is especially important in applications where a small number of oversized particles can cause functional problems.
Because we measure individual particles and generate high-resolution data, we can zoom into specific regions and characterize coarse and fine fractions separately. This capability is unique and extremely valuable.
Can you give an example of how particle sizing improves additive manufacturing applications?
In additive manufacturing, powders must have consistent flow and packing characteristics. Laser diffraction may provide a general distribution profile, but it often underrepresents fines.
Using SPOS, we can clearly detect and quantify fine particles that may influence powder flowability and packing density. In some cases, powders exhibit bimodal distributions that are not easily visible using other techniques.
Understanding the presence of fines allows manufacturers to predict flow behavior and optimize compaction processes for improved part quality.
How is particle sizing applied in inkjet ink development?
Inkjet inks typically contain pigment particles with mean sizes around 100 nanometers. Techniques such as dynamic light scattering are effective for measuring mean size.
However, clogging issues are often caused by particles in the one-micron range or larger. These particles exist in the tail of the distribution and are not easily detected by ensemble techniques.
SPOS allows us to measure the concentration of particles greater than 0.5 or 1 micron with high accuracy. Ink manufacturers use this information extensively for quality control and filtration optimization to prevent nozzle blockage and ensure print reliability.
What role does particle sizing play in pharmaceutical contamination testing?
Particle contamination testing is critical for injectable drugs. Standards such as USP 788 and USP 787 define allowable particle concentrations for parenteral products.
USP 788 applies primarily to small molecule drugs, while USP 787 addresses protein-based therapeutics. The latter is particularly important because protein drugs are extremely valuable, and sample volume must be minimized.
Watch the Webinars Now
Our systems can measure volumes as low as 200 microliters while maintaining reproducibility. Additionally, because we measure down to 0.5 microns, we can detect protein aggregates and evaluate how stress conditions affect aggregation levels.
How is particle sizing used to evaluate emulsion stability?
For injectable emulsions, stability is assessed using two metrics. First, the mean droplet size must remain below a specified threshold, typically 500 nanometers. This can be measured using dynamic light scattering.
Second, we evaluate the tail of the distribution by calculating PFAT5, the volume percent of droplets greater than 5 microns. This measurement directly relates to patient safety and product stability.
SPOS is the preferred technique for PFAT5 analysis because it provides the resolution and sensitivity needed to accurately quantify extremely small volume fractions in the coarse tail.
Are there limitations to SPOS in particle sizing applications?
No single particle sizing technique is appropriate for every sample. If particles fall outside the dynamic range, either too small or too large, alternative techniques such as dynamic light scattering, laser diffraction, microscopy, or sieving may be more appropriate.
The key is always to begin with the intended use of the data. Once the application requirements are clearly defined, the appropriate technique can be selected.
About Mark Bumiller
Mark Bumiller is the Technology Manager for the AMH Instrumentation Division at Entegris. He has more than 40 years of experience in particle characterization and has authored numerous technical papers and application notes on particle size analysis. Over the course of his career, he has delivered hundreds of educational webinars focused on particle sizing methodologies and best practices.
Mark has served on the expert committee for USP 788, contributing to standards governing subvisible particulate contamination in injectable pharmaceuticals. He has also participated in ISO Technical Committee 24, helping develop international standards for particle size measurement and analysis.
Before joining Entegris, Mark held technical roles supporting particle sizing instrumentation and worked extensively with pharmaceutical, semiconductor, and advanced materials manufacturers.
He holds advanced academic training in the physical sciences and has dedicated his career to advancing measurement reliability and repeatability, as well as to developing application-specific particle-sizing solutions.
This information has been sourced, reviewed, and adapted from materials provided by Entegris.
For more information on this source, please visit Entegris.
Disclaimer: The views expressed here are those of the interviewee and do not necessarily represent the views of AZoM.com Limited (T/A) AZoNetwork, the owner and operator of this website. This disclaimer forms part of the Terms and Conditions of use of this website.