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Inductively Coupled Plasma - Optical Emission Spectrometer


Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) can be used for qualitative and quantitative analysis of more than 70 metallic elements and some non-metallic elements in the samples of geology, environmental protection, chemical industry, biology, pharmaceuticals, foodstuffs, metallurgy, agriculture and so on.

Atomic emission spectroscopy is a method in which the atoms of the measured element are excited by thermal or electrical energy and emit characteristic spectra for analysis. ICP-OES is a kind of atomic emission spectroscopy using inductively coupled high-frequency plasma torch as the excitation light source.


The process of ICP-OES analysis is mainly divided into three steps: excitation, spectroscopy and detection.

1.The use of plasma excitation light source to make the sample evaporation vaporization, dissociation or decomposition of the atomic state, the atom may be further ionized into an ionic state, the atoms and ions in the light source excitation luminescence.

2.The light emitted by the light source is decomposed into spectra arranged by wavelength using spectroscopic instruments.

3.The spectra are detected by photoelectric devices, and the specimen is analyzed qualitatively according to the wavelength of the spectra obtained, and quantitatively according to the intensity of the emitted light.

Instrument Structure

ICP-OES equipment mainly consists of five parts: RF generator, plasma- and injection-system, spectroscopy system, detection system and computer system.

1. High-frequency RF generator

R.F generator delivers energy to the plasma through the working coil to maintain the stable discharge of ICP light source, which requires good stability of the output power, easy ignition, small heat generation, stable flame, high effective conversion power, and strong anti-interference ability for different samples and different concentration changes. The current R.F generator mainly has two types of oscillation, i.e. self-excited and it-excited.

2. Plasma and injection system

Plasma generally refers to the ionization degree of more than 0.1% was ionized gas, this gas not only contains neutral atoms and molecules, but also contains a large number of electrons and ions, and the concentration of electrons and positive ions is in equilibrium, from the overall point of view is in neutral.

The sampling system is an extremely important part of the ICP instrument, according to the different sample states can be liquid, gas or solid direct sampling.

  • Liquid sampling device: pneumatic atomizer (copper wire atomizer, cross atomizer, high salt atomizer), ultrasonic atomizer, high-pressure atomizer, micro-atomizer, circulating atomizer, hydrofluoric acid atomizer.

  • Solid feeding device: solid or powder samples directly gasification, vapor or solid aerosol with carrier gas into the plasma, as well as solid or powder samples directly into the plasma or inserted into the plasma method. Commonly used devices are electric spark ablation feeder, laser ablation feeder, electrothermal feeder, inserted graphite cup feeder.

  • Gas injection device: hydride generator, special gas injector.

3. Spectroscopy system

Composite light by dispersive spectroscopy, to get a wavelength-ordered spectrum, can decompose the composite beam into monochromatic light, and observation and recording of equipment called spectrometer. Requirements to have the appropriate wavelength range and wavelength selection, can be detected from the specific region of the radiation source to collect as much light as possible. The performance of the spectroscopic system includes: the size of the dispersion rate, high resolution, the size of the loss of light intensity, the number of moving parts, the number of optical components, the size of the stray light and the effect of good and bad thermostat.

4. Detector

Light irradiation to a certain detection unit, produce a certain amount of charge, and stored in the detection unit, and then read out the way the charge transfer - photoelectric conversion. According to the different ways of reading out, they can be classified into two types:

  • Charge Injection Device (CID): its readout method is to move the charge inside the detection unit to detect voltage changes, i.e., internal charge transfer.

  • Charge Coupled Device (CCD): its readout method is to transfer the charge between the detection unit one by one, moved to a detection unit with a charge-sensing amplifier for readout, that is, the charge transfer between the units.

5. Computer system

This is the brain of the instrument that is responsible for program control, real-time control, data processing and data analysis.

Advantages of ICP-OES

  1. Wide application range: more than 70 elements can be determined.

  2. Multi-element simultaneous detection capability: multiple elements in a sample can be determined simultaneously. Once each sample is excited, different elements emit characteristic spectra, so that a variety of elements can be determined at the same time.

  3. Good selectivity: Each element emits a different characteristic spectrum due to its different atomic structure. In analytical chemistry, this difference in nature, for some elements with very similar chemical properties has a particularly important significance. For example, niobium and tantalum, zirconium and hafnium, dozens of rare earth elements are difficult to analyze by other methods, and emission spectrometry can be no difficulty in distinguishing and determining them.

  4. Low detection limit: general light source up to 10 ~ 0.1ug / g, the absolute value of up to 1 ~ 0.01ug. Inductively coupled high-frequency plasma (ICP) detection limit of up to ng / g level.

  5. Higher accuracy: the relative error of general light source is about 5%~10%, and the relative error of ICP can be up to 1% or less.

  6. Less specimen consumption.

  7. The calibration curve of ICP light source has a wide linear range of 4~6 orders of magnitude, which can be used to determine different contents of elements (high, medium and micro-content).

  8. Common non-metallic elements such as oxygen, sulfur, nitrogen, halogens and other spectral lines in the far-ultraviolet region, the current general spectrometer can not yet be detected; there are some non-metallic elements, such as Te, etc., due to its high excitation potential, the sensitivity is low.


The main applications of ICP-OES include the following:

  1. Material testing: mainly including traditional metal materials and new materials composition testing.

  2. Environment and safety: mainly including the detection of heavy metals in food, food containers and their packaging materials; the detection of harmful heavy metals in toys and children's products and their packaging materials (antimony, arsenic, barium, chromium, cadmium, lead, mercury, etc.); the detection of hazardous materials in electronic and electrical materials; and the detection of hazardous components in cosmetics, detergents and their packaging materials.

  3. Pharmaceuticals: generally used in pharmaceuticals and some health care products and the detection of harmful ingredients and nutrients.

  4. Detection of geology, minerals, agriculture industry: mainly used to analyze the elements in geology, minerals, soil and other materials detection and research.

  5. Detection of any high-purity substances: mainly including high-purity caustic soda of chlor-alkali chemical industry and its raw material trace element analysis and high-purity pharmaceutical intermediates.