Sometimes It’s the Little Things . . . by Mark E. Weiss

When faced with a failed product, we spend a lot of time deconstructing the artifact in an effort to determine what went wrong and why. It could range from material or design failure, to inadvertent chemical exposure, sometimes it is simply an obstruction.

Let’s take as an example a small fluid valve. Be it a medical component or an industrial actuator, the clearances are often very tight and susceptible to seizing by the introduction of a small particle wedging between the moving components of the valve, or possibly obstructing a very small fluid port along the fluid path. From a mechanic’s standpoint the first job is to “clear it out”, the second is to find out “what was it?” These situations occur often and usually at the wrong time to be able to analyze the particle and determine what it is and where it may have come from. Sometimes the particle is lost because of its size, or the person maintaining the device thinks it cannot be identified because it is too small. That is where I am able to help.

Analysis of small particles has become a habit of mine. One of my favorite moments was when a medical client brought a sample to us for identification and it was not immediately visible in the small container in which it was supposedly contained. Even though we both have very good eyesight, neither of us was able to locate the particle. So we placed the container under the microscope and after a few minutes the sample was located. It was a clear, colorless fiber approximately four thousandths of an inch wide and seven thousandths long. The fiber was large enough to analyze, but not large enough to make it a simple task.

Physical properties of a particle can make handling them very difficult. Metal particles tend to slide if you don’t adhere them to a surface, and the static effects of plastic particles can work with or against you. Often the sample sticks to the probe that is being used to transfer the sample, which is perfect, until you try to transfer the sample to a slide and it remains electrically fastened to the probe. Minerals can be affected by both problems.
Ultimately, by one technique or another and a very steady hand, the particles or fibers are transferred to a slide in a petri dish andimmediately the particle jumps to the lid of the petri dish. Who else saw that coming?

But enough about collecting the particles, we need to analyze them. Depending on visual characteristics observed while photographing the sample and preparing it for analysis, we now need to choose which analytical technique(s) should be used. Two of the most often used techniques are Fourier Transform Infrared (FT-IR) Spectroscopy and Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS). In general, FT-IR is used for organic materials such as plastics, oils, food products, textiles, etc. SEM/EDS is generally used for inorganic materials such as metals and minerals. Often the two techniques are used together to narrow the potential identities of the particles.  But wait . . . which test will we run? If we run SEM/EDS, the sample will usually need to be embedded in adhesive to hold it in place. If we run FT-IR afterwards, we may be analyzing the adhesive rather than the sample. There is a lot to think about before this analysis.

Now, FT-IR and SEM/EDS are but two of many available analysis techniques that are often simply described as the “alphabet soup” of instrumentation:  DSC, TGA, DMA, GC-MS, Pyro GC-MS, DHS-GCMS, TOF-SIMS, GC, GPC, LC, and the list goes on. These techniques are all available, but may not necessarily apply to the particle at hand. At this point, the earlier visual evaluation of the particles and the context from which the sample was attained determine the proper course of analysis, ideally with little or no loss of sample.

I’ve been told I am capable of going on about particles for days, so let’s stop here and assume that the analysis went well. From our analysis we have determined that the fiber is polypropylene. Now we can go back through the manufacturing process and search for the source. After some searching, several boxes of non-cleanroom wipes were located in an area where they should not have been. Samples of the wipes were taken back to the lab and analyzed by the same methods. Visually, one of the fibers had a similar cross section, and instrumentally, it compared very well to the original fiber. So, we have a possible source and can pursue the elimination of the source from the assembly environment.

This type of investigation applies to many devices and processes from industrial pneumatics and hydraulics, to drug delivery catheters and other surgical tools–basically anywhere a small particle can get lodged.

So, to summarize: when you locate a problem particle and wonder what it could be, we can help you with that. If you can’t see the particle, but you know it’s there, we can help with that too.

For more information, click here.  Click to contact Mark E. Weiss.