Download Inductively-Coupled Plasma (ICP) Excitation Source

Inductively-Coupled Plasma (ICP) Excitation Source
An inductively coupled plasma (ICP) is a very high temperature excitation source
(7000-8000K).
The sample is nebulized and entrained in the flow of plasma support gas, which is
typically Ar. The plasma torch consists of concentric quartz tubes. The inner tube contains
the sample aerosol and Ar support gas and the outer tube contains flowing gas to keep the
tubes cool. A radiofrequency (RF) generator produces an oscillating current in an induction
coil that wraps around the tubes. The induction coil creates an oscillating magnetic field,
which produces an oscillating magnetic field The magnetic field in turn sets up an oscillating
current in the ions and electrons of the support gas (argon). As the ions and electrons collide
with other atoms in the support gas.
Advantages of ICP-AES are excellent limit of detection and linear dynamic range,
multi-element capability, low chemical interference and a stable and reproducible signal.
Disadvantages are spectral interferences (many emission lines), cost and operating
expense and the fact that samples typically must be in solution.
Laser-Induced Breakdown Excitation Source
When a high-energy laser pulse is focused into a gas or liquid, or onto a solid surface,
it can cause dielectric breakdown and create a hot plasma. For solids the laser pulse also
ablates material into the gas phase. The energy of the laser-created plasma can atomize,
excite, and ionize analyte species, which can then be detected and quantified by atomicemission spectroscopy or mass spectrometry.
Laser-Induced Plasma Excitation Source
A high-power CO2 laser that is focused into a support gas, such as Ar, can maintain a
hot plasma. The energy of the plasma can atomize, excite, and ionize analyte species present
in the support gas, which can then be detected and quantified by atomic-emission
spectroscopy or mass spectrometry. It can also be used in a glow-discharge mode to sputter
analyte atoms off of a solid surface for analysis in the plasma.
Microwave-Induced Plasma Excitation Source
A microwave-induced plama consists of a quartz tube surrounded by a microwave
waveguide or cavity. Microwaves produced from a magnetron (a microwave generator) fill
the waveguide or cavity and cause the electrons in the plasma support gas to oscillate. The
oscillating electons collide with other atoms in the flowing gas to create and maintain a hightemperature plasma. As in inductively coupled plasmas, a spark is needed to create some
initial electrons to create the plasma. Atomic emission is measured from excited analyte
atoms as they exit the microwave waveguide or cavity.
Spark and arc atomic emission spectroscopy
Spark or arc atomic emission spectroscopy is used for the analysis of metallic elements
in solid samples. For non-conductive materials, the sample is ground with graphite powder to
make it conductive. In traditional arc spectroscopy methods, a sample of the solid was
commonly ground up and destroyed during analysis. An electric arc or spark is passed
through the sample, heating it to a high temperature to excite the atoms within it. The excited
analyte atoms emit light at characteristic wavelengths that can be dispersed with a
monochromator and detected. As the spark or arc conditions are typically not well controlled,
the analysis for the elements in the sample is qualitative. However, modern spark sources
with controlled discharges under an argon atmosphere can be considered quantitative. Both
qualitative and quantitative spark analysis are widely used for production quality control in
foundries and steel mills.