Inductively coupled plasma (ICP) is the most widely used plasma source in atomic emission spectroscopy (AES), also known as Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The ICP source, or torch, consists of three concentric quartz tubes with argon gas flowing through them. A spark from a Tesla coil initiates the ionization of argon, generating a high-temperature plasma.
The ions and electrons produced interact with the fluctuating magnetic field created by a water-cooled induction coil powered by a radio-frequency generator. This interaction leads to ohmic heating, forming a high-temperature plasma and providing an optimal environment for elemental analysis. Sample introduction in ICP-AES can be achieved using different methods, such as a concentric glass nebulizer or electrothermal vaporization. In the former, the sample is transported by the Bernoulli effect with the help of high-velocity argon gas, forming fine droplets that enter the plasma. In the latter, the sample is vaporized in a furnace before being introduced into the plasma via a stream of argon.
Configurations for ICP spectrometers include radial or axial viewing. Horizontally oriented, axially viewed plasma is ideal for high-sensitivity analyses. It features a unique cooled cone interface (CCI) that prevents the optics from considering the cooler plasma tail, reducing interferences and improving the system's tolerance to high dissolved solids. Vertically oriented, radially viewed plasma is suitable for challenging applications, such as the analysis of oils, organic solvents, geological/metal digests, and high total dissolved solids (TDS) solutions.
Isothermal contours depict the range of temperatures experienced by sample atoms in the plasma during their residence time before reaching the observation point. This results in more complete atomization and fewer chemical interferences. The ICP source in AES offers numerous advantages, including chemically inert atomization, uniform temperature distribution, linear calibration curves over a wide range of concentrations, and significant ionization, making it an excellent choice for ICP-MS applications.
Inductively coupled plasma, or ICP, is a widely used plasma source in atomic emission spectroscopy.
It employs a plasma torch consisting of three concentric quartz tubes with flowing argon gas, which is ionized by a spark from a Tesla coil.
The resulting ions and electrons interact with the fluctuating magnetic field created by a water-cooled radio-frequency induction coil.
This interaction leads to ohmic heating, forming a high-temperature argon plasma with a brilliant white core and a flame-like tail.
In ICP–AES, a concentric glass nebulizer is used to transport the sample with the help of high-velocity argon gas to form fine droplets by the Bernoulli effect—that enters the plasma.
Alternatively, electrothermal vaporization can be employed, where the sample is vaporized in a furnace, and an argon stream carries it into the plasma.
The plasma source offers various advantages, like atomization in a chemically inert environment that prevents refractory oxide formation and prolongs the analyte's lifetime.
Additionally, it maintains a relatively uniform temperature cross-section, reducing occurrences of self-absorption and self-reversal.
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