Atomic Spectroscopy for Metal Analysis - Fundamentals of Environmental Sampling and Analysis - page 238

Another source of chemical interference is the formation of refractory metal
compounds, which prevents the test element to form atomic atoms thereby causing
negative interference. Refractory metal phosphates (e.g., Ca 2 P 2 O 7 ) can be avoided
by adding releasing agents such as strontium ion or lanthanum ion, which will
preferentially combine with phosphate and prevent its reaction with calcium. The
formation of refractory metal oxides (e.g., CaO) can be avoided by the use of high-
temperature flame (nitrous oxide-acetylene rather than air-acetylene).
Physical interference: Physical interference is caused by the variation of
instrumental parameters that affect the rate of sample uptake in the burner and
atomization efficiency. This includes variations in the gas flow rates, variation in
sample viscosity due to temperature or solvent, high solids content, and changes in
flame temperature. Physical interference can be corrected by the use of internal
standards.

Other Considerations

Other considerations include sample throughput, cost, ease of use, and availability
of proved methodology. The analytical time for metal analysis using atomic spec-
troscopy is of less concern compared with the analysis of organic compounds using
chromatographic instruments. The time required for elemental analysis ranges from
a few seconds to several minutes. However, one fundamental consideration is the
single-element technique (FAA and GFAA) vs. multi-element technique (ICP-OES
and ICP-MS).
The single-element technique requires specific light source and optical para-
meters for each element to be determined. Therefore, the lamp must be changed
between each element. Although FAA or GFAA now has automated multi-element
systems, it is still considered to be a single element method. A typical run for a single
element takes only 3-10 s, whereas GFAA takes much longer, approximately 2-
3 min for each element, because the system needs to remove solvent and matrix
components prior to atomization. The multi-element technique (ICP) can determine
10-40 elements per minute in individual samples. ICP-MS is typically 20-30
element determinations per minute depending on such factors as the concentration
levels and required precision. For both ICP-OES and ICP-MS methods, the time is
only limited by the equilibrium time needed between new sample and the plasma
(typically 15-30 s).
Capital costs for atomic spectroscopic equipment in the increasing order are FAA

< ICP-MS (Fig. 9.11). There is a considerable variation in

cost between instrumentation for the same technique depending on the features (e.g.,
manual vs. automation).
In terms of skill required and ease of operation, FAA is the easiest to use,
followed by GFAA, where skills to optimize operational parameters are needed. Skill
requirements for ICP are intermediate between FAA and GFAA. ICP-MS requires
operator skills similar to ICP-OES and GFAA.
As a general selection guide to summarize the above discussions, FAA and ICP-
OES are favored for moderate to high concentration, while GFAA and ICP-MS are

GFAA < ICP-OES <<