Atomic Spectroscopy for Metal Analysis - Fundamentals of Environmental Sampling and Analysis - page 237

Table 9.2 Atomic spectroscopy interferences

Method of compensation a Technique Type of interferences

FAA Ionization Ionization buffer

Chemical Releasing agent or nitrous-acetylene flame

Physical (self-absorption) Dilution, matrix matching, or method of additions

GFAA Physical and chemical Stabilized temperature platform furnace (STPF)

condition

Molecular absorption Zeeman or continuum source background correction

Spectral Zeeman background correction

ICP-OES Spectral Background correction or the use of alternative

analytical lines, IECs or MSF

Matrix Internal standardization

ICP-MS Mass overlap Interelement correction, use of dynamic reaction

cell (DRC) technology, use of alternate mass
values or higher mass resolution

Matrix Internal standardization

a Details of these compensation methods can be found in Skoog et al. (1997). IEC¼Interfering element
correction; MSF¼Multicomponent spectral fitting. Zeeman background correction¼A method to
correct for background absorption in furnace AA that uses a magnetic field around the atomizer. The
field splits the energy levels of the absorbing atoms and allows discrimination of atomic absorption
from other sources of absorption. (Courtesy pf Perkin-Elmer, Inc.)

standard additions method for calibration (see Example 9.2 in Section 9.4) or
background correction. With background correction, the standard is added to a
separate aliquot of the sample and the increase in the measured signal is proportional
to the concentration added. In this manner, the standard is subjected to the same
matrix as the sample. The background absorption interference, particularly serious
in complex biological and environmental samples, can be readily eliminated by an
automatic background subtraction (the resonance line absorption from the hollow-
cathode lamp minus the broadband absorption of a continuum source).
Chemical interference: The chemical interference is a result of the formation of
undesired chemical species during the atomization process, such as ions and
refractory compounds (Fig. 9.1). Their effects are more common than spectral ones,
but can be frequently minimized by selecting a proper operating condition.
Chemical interferences are more common in low-temperature systems such as FAA
and GFAA than in high-temperature ICP systems.
When easily ionized elements (such as alkali and alkaline earth elements) are
measured, chemical ionization interference occurs as we are measuring the non-
ionized atoms. The ionization of these easily ionizable elements will decrease the
signals for both absorption and emission, hence creating negative interference.
When other elements are measured, the presence of such elements will also cause
positive interference. This is because the free electrons added to the flame from
alkali or alkaline elements will suppress the ionization of the test element.