Air Quality Criteria for Lead Volume II of II - (NEPIS)(EPA) - US ...

With EDS, a single Si-Li crystal detector is used in conjunction with a multichannel
analog-digital converter (ADC) to sort electrical pulses (with heights approximately proportional
to the quantum energy of the photon that generated them), producing a spectrum of energy
(wavelength) versus counts. The net area under a particular peak (elemental line) is proportional
to its concentration in the sample. For quantitative analyses, corrections similar to WDS analysis
must be performed. Although EDS detectors are more efficient than WDS, detection limits are
significantly greater (~1000 ppm), because of elevated backgrounds and peak overlaps.
For speciation analysis, the EDS system must NEVER be used as the primary detector, as
numerous errors in species identification are often made. These are generally the result of
higher-order X-ray line overlaps.
This technique has been routinely used for site characterizations (Linton et al., 1980;
Hunt et al., 1992; Camp, Dresser, and McKee (CDM), 1994; U.S. Environmental Protection
Agency, 2002). Currently this technique offers the most complete data package on metal
speciation than any of the other tools. The method is relatively fast and inexpensive, available,
and provides all of the required information for bioavailability assessments (i.e., particle size,
species, lability, and sourcing). A number of limitations still need to be addressed including:
(1) its inability to quickly isolate a statistically significant population of particles in soils with
low bulk metal concentrations (