Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) Information

Inductively coupled plasma optical emission spectroscopy (ICP-OES), sometimes referred to as ICP-atomic emission spectroscopy, is the technique of choice for many applications that require analyzing a sample for its elemental content. Typical samples include those in the environmental, metallurgical, geological, petrochemical, pharmaceutical, materials, and food safety arenas. It can be applied to varying sample types such as aqueous and organic liquids and solids. Some of these sample types need specific sample preparation techniques or the use of specific accessories to allow the sample to be introduced into the ICP-OES instrument.

The advantages of using ICP-OES over other elemental analysis techniques such as inductively coupled plasma mass spectrometry (ICP-MS) or atomic absorption spectrometry (AAS) include its wide linear dynamic range, high matrix tolerance, and the enhanced speed of analysis that can be achieved.

What is ICP-OES?

A plasma is a gas, in this case argon, which contains a significant number of argon ions. The plasma is formed by seeding the argon gas passing through a plasma torch with electrons. The electrons are accelerated and collide with argon atoms releasing more electrons and forming argon ions. Elements, in the form of atoms, are introduced into the plasma. A proportion of theses atoms will be become ionized within the plasma. When an atom or ion is excited within the plasma, its electrons move from a lower to higher energy level (figure 1). Upon relaxation of these electrons to their initial 'ground' state, energy is emitted in the form of photons. The emitted photons possess wavelengths that are characteristic of their respective elements.

Figure 1. Excitation of an atom by plasma.

Figure 1. Excitation of an atom by a plasma.

One element can have multiple electron excitations and relaxations; therefore, it can have multiple characteristic wavelengths. An example of an emission spectrum for calcium is shown in figure 2.

Visible emission spectrum of calcium

Figure 2. Emission spectrum of calcium in the visible range.

ICP-OES takes advantage of the unique emission spectra of elements to identify and quantify them.

In this section on ICP-OES, you will:

Understand the systems and technologies that drive ICP-OES
Learn which sample types can be analyzed by ICP-OES and what conditions must be considered during sample preparation and introduction
Recognize and correct for factors that interfere with accurate data analysis