With the right instruments and a little time, Craig Cook can tell where you’ve been by looking at the atoms in your hair — or, at least, he can tell where you haven’t been.

Before coming to the University of Wyoming, Cook managed the isotopic analysis lab at the University of Utah, where he and his colleagues helped law enforcement identify the victim in a now famous cold case: Saltair Sally.

Sally’s remains were found by duck hunters in 2000, near the Great Salt Lake.

“Most of it had been mucked around with,” Cook said. “It had been there a while. The animals had gotten to it. There were some bones. There was no ID. There was one piece of jewelry. Female with relatively long hair — that’s all they knew.”

For more than a decade, Sally went unidentified, until investigators approached Cook and his colleagues, asking about isotopic analysis, a way of determining what kind of atoms make up a given substance.

“We analyzed her hair — it was quite long — and we saw in that hair, looking at her oxygen isotopes, a very distinct pattern that she was traveling from one place to another place and back again and did this repeatedly over a two-year period.”

The analysis told law enforcement where to to look, Cook said.

“Based on that information, they found a missing person report of a young lady from Salt Lake who was routinely traveling from Salt Lake to Seattle and back, which was right through the corridor we gave them,” he said, adding DNA evidence confirmed the missing person and Sally were one and the same.

The science

The case of Saltair Sally is just one example of what researchers can do with isotopic analysis.

As director of UW’s Stable Isotope Facility, Cook runs a lab capable of determining whether an animal was wild or domesticated, the source of a water contaminants and a drug’s country of origin.

At the heart of all these “gee-whiz” uses for isotopic analysis — Cook’s description of his lab’s flashier capabilities — are the isotopes themselves.

Atoms are defined by the number of protons that constitute them. An oxygen atom has eight protons. A carbon atom has six.

Typically, a carbon atom will also contain six neutrons, giving it an atomic mass of approximately 12 once the protons and neutrons are added together. But a carbon atom is capable of containing more neutrons, raising that mass to 13 or 14. Carbon 12, carbon 13 and carbon 14 are all isotopes of carbon, though they are far from the only ones.

“We’re looking at one-neutron differences in molecules,” Cook said. “When you think about it, it’s pretty clever.”

Carbon 12 and 13 are known as “stable” isotopes, because they do not change, which makes them useful to researchers like Cook.

He used ocean water as an example. When water from the ocean evaporates, lighter molecules — containing atoms with relatively low isotope numbers — will be evaporated first because they have weaker bonds.

“The analogy I give to the K-12 kids is this is very much like a teenager,” Cook said. “They’re going to take the easy route. You give them a job, they’re going to go the path of least resistance.”

As water from the Pacific Ocean — in the form of clouds — makes its way inland and over the mountains, it drops its heaviest molecules, or those containing heavier isotopes. This process results in different places having different concentrations of isotopes in their water — differences which can be mapped, giving researchers what is known as an “isoscape.”

“Tap water — drinking water — across the U.S. changes isotopically,” Cook said. “Warmer regions tend to be much heavier isotopically than cold regions. A place like Laramie is very light isotopically. Florida is very heavy.”

And what is in the water is also in the people. The oxygen molecules present in, for example, someone’s hair tell a story about where they have been, assuming that person drinks local water and not bottled.

“The oxygen in your hair comes from the water you drink, not the food you eat,” Cook said. “Forensically, this is really quite important.”


Isotopes can also tell researchers where certain elements are coming from. For example, Cook worked with the Casper Aquifer, isotopically analyzing the nitrogen in the water supply.

“For many years, what they were doing up there was measuring the nitrate concentration in their wells, and some of them were really high on an EPA-contaminant level, some not so much,” he said. “And if it got really high, they worried about it. The question they could never answer was where that nitrate comes from. They knew it was a lot of it, but they didn’t know its source.”

The source of the nitrogen can be determined isotopically, Cook said.

“If you are a nitrate that comes from a septic system … you look very different in your nitrogen isotopes than you do if you’re, say, from atmospheric deposition or from plants,” he said. “There’s some overlap, but they’re pretty distinct.”

Federal law enforcement agencies have found other uses for isotopic analysis as well, Cook said.

“You can use carbon, nitrogen, oxygen (and) hydrogen isotopes in conjunction with each other to look at the source of drugs,” he said. “There’s only five or six or seven regions in South America where they actually grow coca, because it just doesn’t grow outside them. Those are all very distinct isotopically, so you can take that cocaine, do whatever you do to it and say, this came from this place.”

The isotope lab works with gases, meaning it must burn small amount of whatever it looks at.

“Let’s say I want to take a look at the oxygen isotopes in your hair,” Cook said. “I can’t take your hair and stuff it into my instruments and (have it) give me numbers. I have to convert it to a gas.”

The gas is then bombarded with electrons, he said.

“Every now and then, one of our gas molecules gets hit by one of these electrons and when we do that, we form what’s called an ion,” Cook said. “All it means is we knocked an electron off the CO2 molecule. So it’s still CO2, it just has a charge now.”

These ions are shot past a large magnet, which is set up to repel them.

“Here’s the clever part: if you’re light, you get pushed farther than if you’re heavy,” Cook said. “We can separate those and count them.”

The lab is left with an analysis of the substance’s isotopic make-up.

The lab

The Stable Isotope Facility works with researchers from all areas of campus, from anthropology to zoology, assisting investigators from all fields in collecting data which is later interpreted by those outside researchers.

Faculty Director Dave Williams said the isotope lab is one of many cross-disciplinary labs at UW.

“It’s important to develop efficiencies and collaboration in the way we do research at big universities, where oftentimes different researchers are in different locations across campus,” he said. “The stable isotope lab is one really successful example of how centralizing the scientific instrumentation and building core facilities for interdisciplinary research activities can really move the university forward and help the university become nationally competitive.”

This mixing of otherwise disparate areas of investigation makes for a stimulating environment, Lab Technician Dori Wolfe said. As a history major, Wolfe said she enjoys hearing about varied research happening across campus.

“We always get people coming in talking about their projects,” she said. “Everybody always has a new project.”

The planned Science Initiative Facility is designed to add core facilities, usable by all on campus. The State Legislature will likely decide during the upcoming budget session whether to release the previously appropriated funds necessary for construction of the facility.

“There’s different reasons to invest and develop a centralized core facility,” Williams said. “One is obviously to be able to manage the very complicated scientific instrumentation and provide access to researchers, but an equally important reason to have such facilities is to provide a training ground for students — undergraduate students, graduate students, post-doctoral researchers.”

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