To crack the toughest particle identifications, look at what holds those particles together.

Understanding Small

If you can see it, it’s not really small. For Senior Research Chemist Gretchen Shearer, Ph.D., that’s often the first lesson for clients who are new to microscopy.

“What you can perceive with your eye without magnification – once you put that under the microscope, it’s pretty large,” Dr. Shearer says. In her role with McCrone Associates, Dr. Shearer often finds herself investigating and identifying unknown substances. She and her colleagues are often asked to identify materials given a sample of just a few particles.

And the best way to do that is take an even closer look.

“When we talk about small, we’re talking about small particles,” Dr. Shearer says. “We can do one or two or three analyses just on that particle! But there’s an even smaller element, the actual chemical bonds on elements that tell us what they are. And their function – what they do in life, or in an industry – is also based on those chemical bonds.”

That means the best approach to particle identification is often to look closer than the particle itself – at the chemical bonds that determine the particle’s composition and dictate its function.

Deciding the best way to identify those chemical bonds means solving a unique puzzle. And that’s just what Dr. Shearer and her colleagues love to do.

“My favorite genre of literature is mysteries,” Dr. Shearer says. “Ever since I was a kid I’ve loved the problem-solving aspect of science… The forensic aspect. I love the fact that every day brings a different sample.”

And since no two particle identification projects are the same, the puzzles are a little different every day as well.

McCrone scientists work collaboratively, addressing each new mystery to the combined of experience available across their teams. When a new sample arrives at the investigative lab, Dr. Shearer says, chances are good that she or one of her colleagues will have seen something similar before. That combined experience makes for a helpful starting point. And once the team has formed a plan, it’s time to gather information.

Materials scientists have several techniques available to study samples at the chemical-bond level, including not just standard microscopy but infrared microscopy, energy-dispersive x-ray spectroscopy (EDS) and x-ray diffraction.

“All of those different scientific methods give us different pictures – different parts of the puzzle,” Dr. Shearer says. The more pictures she and her colleagues gather of the chemical bonds in a substance, the easier it becomes to solve the puzzle and identify the substance.

And because these measurements are made at the microscopic level, that’s just as true if the substance in question is only a single particle.


Gretchen L. Shearer is a senior research chemist at McCrone Associates and an instructor with Hooke College of Applied Sciences. She is responsible for chemical analysis using infrared spectroscopy, Raman microspectroscopy, gas and liquid chromatography, polarized light microscopy and microchemical techniques. Gretchen holds a Ph.D. in Archaeological Chemistry from the University of London and completed a fellowship at the Metropolitan Museum of Art. She has been with McCrone since 1995.