Atomic Emission Spectroscopy (AES, OES)
Introduction
Atomic emission spectroscopy (AES or OES [optical emission spectroscopy])
uses quantitative measurement of the optical emission
from excited atoms to determine analyte concentration. Analyte atoms in
solution are aspirated into the excitation region where they are desolvated,
vaporized, and atomized by a flame, discharge, or plasma. These high-temperature
atomization sources provide sufficient energy to promote the atoms into
high energy levels. The atoms decay back to lower levels by emitting light.
Since the transitions are between distinct atomic energy levels, the emission
lines in the spectra are narrow. The spectra of samples containing many
elements can be very congested, and spectral separation of nearby atomic
transitions requires a high-resolution spectrometer. Since all atoms in
a sample are excited simultaneously, they can be detected simultaneously
using a polychromator with multiple detectors. This ability to simultaneously
measure multiple elements is a major advantage of AES compared to atomic-absorption
(AA) spectroscopy.
Schematic of an AES experiment
Instrumentation
As in AA spectroscopy, the sample must be converted to free atoms, usually
in a high-temperature excitation source. Liquid samples are nebulized and
carried into the excitation source by a flowing gas. Solid samples can
be introduced into the source by a slurry or by laser ablation of the solid
sample in a gas stream. Solids can also be directly vaporized and excited
by a spark between electrodes or by a laser pulse. The excitation source
must desolvate, atomize, and excite the analyte atoms. A variety of excitation
sources are described in separate documents:
Since the atomic emission lines are very narrow, a high-resolution polychromator
is needed to selectively monitor each emission line.
Picture of an inductively-coupled plasma atomic emission spectrometer
JavaScript
tour of an ICP-AES Spectrometer
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