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

Modern ICP/AES systems offer a choice of either axial viewed plasma (horizontal),
which provides greater sensitivity (DL= 0.8 µg Pb/L), or radial (vertical) viewed plasma, which
performs best with high total dissolved samples (DL = 5.0 µg Pb/L).
The development of reaction or collision cells have expanded the capabilities of ICP/MS
and lowered detection limits for many elements that were difficult to analyze because of
interferences such as Se, As, Ti, Zn, Ca, Fe, and Cr. The cells provide efficient interference
(isobaric, polyatomic, and argide) removal independent of the analyte and sample matrix by
using various reaction gases (H2, He, NH3), eliminating the need for interference correction
equations.
Speciation Tools
A wide variety of analytical and chemical techniques have been used to characterize a
metal’s speciation (as defined above) in various media (Hunt et al., 1992; Manceau et al., 1996,
2000a; Welter et al., 1999; Szulczewski et al., 1997; Isaure et. al., 2002; Lumsdon and Evans,
1995; Gupta and Chen, 1975; Ma and Uren, 1995; Charlatchka et al., 1997). Perhaps the most
important factor that one must keep in mind in selecting a technique is that, when dealing with
metal-contaminated media, one is most often looking for the proverbial “needle in a haystack.”
Therefore, the speciation technique must not only provide the information outlined above, but it
must also determine that information from a medium that contains very little of the metal.
As illustrated in Figure AX7-1.1.5, for a Pb-contaminated soil, less than 1% (modally) of a
single species can be responsible for a bulk metal’s concentration above an action level. This
factor is even more significant for other metals (i.e., As, Cd, or Hg) were action levels are often
below 100 mg/kg.
Of the techniques tested (physicochemical, extractive, and theoretical), the tools that have
been used most often to evaluate speciation for particle-bound metal include X-ray absorption
spectroscopy (XAS), X-ray diffraction (XRD), particle induced X-ray emission (PIXE and
µPIXE), electron probe microanalysis (EPMA), secondary ion mass spectrometry (SIMS),
X-ray photoelectron spectroscopy (XPS), sequential extractions, and single chemical extractions.
The tools that have been used most often to evaluate speciation for metal particles in solution
include the following computer-based models: MINTEQL, REDEQL2, ECOSAT, MINTEQA2,
HYDRAQL, PHREEQE, and WATEQ4F. These tools are briefly described below.
AX7-11