Inductive coupled plasma (ICP)

Author: Hans-Jürgen Schwarz
English Translation by Sandra Leithäuser

back to Analysis of Salts

Abstract

An inductively coupled plasma (ICP) is a type of plasma source in which the energy is supplied by electric currents produced by electromagnetic induction, that is, by time-varying magnetic fields. The inductively coupled plasma is used in a the high-frequency field (27 MHz) ionized gas (argon), which serves as an atomization and excitation medium for the sample. It is used in conjunction with atomic emission spectroscopy (ICP-AES) or with mass spectrometry (ICP-MS). It can detect very low concentrations of the analyzed elements in the sample, in the order of one millionth (ppm) or one billionth part(ppb).

Introduction

ICP serves to excite atoms, for example in the atomic emission spectroscopy (ICP-AES) or in coupling with a mass spectrometer. The inductively coupled plasma is an ionized gas (argon) in the high-frequency field (27 MHz). It serves as a medium for atomization and excitation of the sprayed liquid or dissolved sample. In emission spectroscopy ICP can be used with various optical and electrical systems, combined with either simultaneous or sequential multi-element spectrometers.

Principle: The ICP torch is made of three concentrically arranged tubes of quartz glass. Aerosol laden gas (i.e. gas and the analyte) flows through the inner tube. Plasma gas (usually argon) is fed into the central tube and the exterior tube directs a flow of cooling gas. Because the sample is kept inside the plasma torch for a long time and due to the high temperatures (6000- 8000 K) inside the torch, a very high state of excitation is achieved. The excited atoms, (formed in the plasma) emit light with a characteristic wavelength, which is registered as emission spectrum.

ICP emission spectroscopy is a powerful analytical method that enhances atomic absorption spectroscopy, but cannot replace it completely.

Abbildung: Messanordung eines Emissions –Spektrometers (oben) und ICP-Anregung  

Advantages:

• Matrix effects (e.g. falsified blanks and changing measurement sensitivities by solvents that act similarly to the analyte or interact with the analyte) are significantly lower in the ICP than in the AAS.
• ICP is largely free of chemical and ionization interference. The long- span dynamic range (4-6 orders of magnitude) allows the simultaneous determination of major and minor components and traces. Therefore a large number of elements can be quickly determined.
• In the study of salts or salt-forming ions, this method is particularly useful for determining K⁺, Na⁺, Ca²⁺, Mg²⁺.

Disadvantage:

• Anions cannot be detected.
• Not a non-destructive method.

In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. A very high heating over a few thousand K leads to ionization, thus turning it into a plasma, containing charged particles.

Inductive Coupled Plasma, method for analysing chemical elements.

a method to determine chemical elements employing the absorption of optical radiation (light) by free atoms in the gaseous state.