Chromatographic and Other Analytical Capabilities
Most radiolysis experiments yield reaction products
in the micromolar or lower concentration range. Usually this is
done deliberately: Radiation doses intense enough to produce higher
yields also produce concentrations of radicals large enough to interact
with each other instead of other solute molecules. However, such
low concentrations place a considerable demand on the analytical
resources of the radiation chemist.
At the Radiation Laboratory, a number of chromatographic and spectroscopic
tools are in use to detect and analyze minute concentrations of
reaction products. High-pressure liquid chromatography (HPLC) or
capillary electrophoresis are employed to separate products and
quantify yields. Detection techniques applied to the separated samples
include optical absorption spectroscopy, refractive index measurement,
and mass spectrometry. Each of these methods has its own strengths
and weaknesses. Optical absorption is probably the most informative,
except for molecules that have no significant absorption spectrum
in the visible or near-UV wavelengths.
Ion chromatography is a variant of HPLC which uses conductivity
to analyze for the presence of ions, particularly inorganic ions,
in solution. In the radiolysis of halogenated organic molecules,
for instance, the ion chromatograph of the halide ions is an excellent
way to measure yields of halo-organic destruction processes.
Several gas chromatographs and a GC/mass spectrograph are available
for separation and detection of volatile samples.