The presence of particulate matter in devices is a common concern. Often the particles are of obvious origin, but sometimes the origin is unclear. When the origin is unclear, analysis of the particles along with a bill of materials for the device/project may combine to identify the source. In other cases, multiple components may come together to form a new compound or precipitate that is different from the materials used in the system and a more complex analysis is required.
Before we get too far ahead, let’s talk for a moment about particle size. What is considered a small particle? It depends where you stand. For some applications, anything under 0.050” diameter would be acceptable as it would not cause any adverse mechanical effects. In other applications, the maximum size limit may be much smaller. Some drug delivery catheters may have multiple holes as small as a few microns. Now the 0.050” particle becomes a relative boulder.
Analytical techniques usually have minimum sample sizes, which can range from a single particle too small to see without magnification, to techniques which require several grams of material per analysis. Also, depending on the size and physical characteristics of the particulate, they may be difficult to capture and prepare for analysis.
Determining what type of analysis to use in the identification of the captured particles can be as complex as the problem itself. A myriad of analytical techniques exists to choose from, each with their benefits and limitations. Suitability of the sample for the analysis is one factor, but variables like limited sample quantity, reactivity, etc. also need to be considered. Interferences are of concern as well, such as the sample being embedded in a substrate, or coated in a liquid.
Lastly, are we allowed to destroy the sample in the process of identifying it? Is the sample the only one in existence? Or do we have many to work with?
Sometimes, what appeared to be a simple analysis of a particle may have become a much more complex analysis.