Page 34 - AAS & AES & FES 01082016_Neat

ATOMIC EMISSIVE SPECTROMETRY WITH PLASMAS
Atomic emissive spectrometry (AES) can be performed with apparatus similar to that

shown in the block diagram previously, where the flame is replaced with either plasma or
electrodes. Argon plasmas are used most often for non-flame AES. The high temperatures that

are achieved in argon plasmas cause more efficient excitation of atoms and ions than is achieved
with flames. As a result, the intensities of the emitted lines are greater and more spectral lines are

observed.

The wavelength selector for an instrument that uses plasma is a narrow bandpass
monochromator. The wavelength of the monochromator as well as the other functions of the

spectrometer are generally controlled by a microcomputer. Various detectors can be used

including photomultiplier tubes and diode arrays. Several wavelengths can be simultaneously
monitored or the wavelengths can be sequentially scanned. The readout devices that are used

with the spectrometers include cathode-ray tubes, recorders, and line printers. A plasma is a form
of matter that contains a significant percentage (>1%) of electrons and ions in addition to neutral

species and radicals. Plasmas are electrically conductive and are affected by a magnetic field.
The plasmas used in emission spectroscopy are highly energetic, ionized inert gases. The

most common plasma in commercial use is the argon ICP. Two other commercial plasma

sources are the Direct coupled plasma (DCP), also usually supported in argon and the helium
microwave induced plasma (MIP). The temperature of a plasma excitation source is very high,

from 6500 to 10,000 K, so almost all elements are atomized or ionized and excited to multiple

levels. The resulting emission spectra are very line-rich, which necessitates the use of high-
resolution spectrometers to avoid spectral overlap.

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