For release: Sept. 9, 1999
Contacts:
Sam Houk, Ames Laboratory, (515) 294-9462
Saren Johnston, Ames Lab Public Affairs, (515) 294-3474
AMES, Iowa -- Sam Houk, a senior chemist at the U.S.
Department of Energy's Ames Laboratory, has added a new twist to an old technique, and the
outcome has dramatically improved the process for identifying the chemical forms of
ultratrace metals in biological and environmental materials. The unique experiment holds great promise for helping scientists better
understand how both radioactive and nonradioactive elements bind to proteins and DNA at
very low concentrations.
Using a novel extension of inductively coupled plasma-mass spectrometry, a time-honored
analytical technique pioneered at Ames Laboratory and now used throughout the worldwide
research community, Houk can determine the total amounts of trace metals in biological
specimens at parts-per-trillion levels. And, his ICP-MS method is faster and more
sensitive and selective than conventional schemes.
Houk's experiment relies on a special type of chromatographic separation called size
exclusion chromatography in combination with a state-of-the-art magnetic sector mass
spectrometer and an inductively coupled plasma -- a very hot argon gas.
In the experiment, chromatographic separation of the compounds of interest provides
chemical information, in particular the molecular weights of the proteins. The
chromatography work is crucial because it reveals the percentage of a trace element in a
sample that is bound to particular biomolecules.
"If we just put the entire sample in the ICP, it would only measure the total amounts of the individual elements present,"
said Houk. "It would not tell us that,
say, 90 percent of an element is in a particular molecular weight range, and 10 percent is
in a different fraction."
After chromatographic separation, the sample is automatically injected into a nebulizer
that produces a mist of fine droplets. The droplets dry into aerosol particles and pass
into the ICP where they are converted to atomic ions (electrically charged atoms) that are measured by the mass spectrometer. The resulting measurements help scientists learn more
about the effects of unusual elements in biological and environmental materials.
Houk's experiment is applicable to almost any element in practically any kind of
biological system -- the main exceptions are carbon, nitrogen, oxygen and hydrogen, common
elements that are always present.
Just as there are few limits regarding the elements to which Houk can apply his
experiment, there are also seemingly endless potential applications. Work for the
Department of Energy deals with determining the fate of radionuclides in the ecosphere, a
major concern in the cleanup of nuclear facilities. The conversion of radionuclides to
atomic ions in the ICP considerably reduces the time required for measuring nuclides with
long half-lives.
Houk said there may also be medical uses for his experiment and noted the interest in
selenium compounds as an example. "These are marketed as health foods and as
preventive treatments for cancer, and they are also touted to delay the onset of AIDS
symptoms, but there have been few direct measurements of the role of selenium in this
regard."
Agricultural applications could involve extracting proteins or other macromolecules from
grains and measuring the binding of trace elements.
Houk's experiment could also be used to measure trace metals in synthetic polymers if they
could be brought into solution. "There's some interest in this since the processing
procedures for polymers usually involve exposing the material to metals," he
explains. "There's a question about where the metals wind up in the final
product."
Houk's experiment can accommodate just about any liquid sample as long as it has an
inorganic element in it. Now his goal is to improve selectivity in identifying the
biological compounds. "The experiment gives us a crude separation of compounds
based on molecular weight," he said. "A chromatographic fraction for an element
could include many different proteins that contain that element. We want to separate those
proteins more effectively and develop mass spectrometric measurements that will be
sensitive to the particular molecule."
Ames Laboratory is operated for the Department of Energy by Iowa State University. The Lab
conducts research into various areas of national concern, including energy resources,
high-speed computer design, environmental cleanup and restoration, and the synthesis and
study of new materials.
Last revision: 9/10/99 dbm