Atomic emission spectroscopy (AES) is a chemical analysis method that uses the intensity of light emitted by a flame, plasma, arc or spark at a specific wavelength to determine the amount of an element in a sample.
The wavelength of the atomic spectral line gives the identity of the element, while the intensity of the emitted light is proportional to the number of atoms of the element. This is the essence of atomic emission spectroscopy. It allows you to analyze elements and physical phenomena with impeccable accuracy.
Spectral Analysis Methods
A sample of the material (analyte) is introduced into the flame in the form of a gas, a sprayed solution, or using a small loop of wire, usually platinum. The heat from the flame evaporates the solvent and destroys the chemical bonds, creating free atoms. Thermal energy also translates the latter into excited electronic states, which subsequently emit light when they return to their previous form.
Each element emits light with a characteristic wavelength, which is scattered by a grating or prism and is detected in the spectrometer. The technique that is most often used in this method is dissociation.
A frequent application of flame emission measurement is alkali metal regulation for pharmaceutical analytics. For this, the atomic emission spectral analysis method is used.
Inductively coupled plasma
Inductively coupled plasma atomic emission spectroscopy (ICP-AES), also called inductively coupled plasma optical emission spectrometry (ICP-OES), is an analytical method used to detect chemical elements.
This is a type of emission spectroscopy that uses inductively coupled plasma to produce excited atoms and ions that emit electromagnetic radiation at wavelengths characteristic of a particular element. This is a flame method with a temperature in the range from 6000 to 10000 K. The intensity of this radiation indicates the concentration of the element in the sample used when applying the spectroscopic method of analysis.
Key Links and Diagram
ICP-AES consists of two parts: ICP and optical spectrometer. The ICP torch consists of 3 concentric quartz glass tubes. An output or “working” coil of a radio frequency (RF) generator surrounds part of this quartz burner. Argon gas is commonly used to create plasma.
When the burner is turned on, a strong electromagnetic field is created inside the coil with the help of a powerful radio frequency signal flowing through it. This RF signal is generated by an RF generator, which, in essence, is a powerful radio transmitter that controls the “working coil” in the same way as a conventional radio transmitter controls a transmit antenna.
Typical instruments operate at 27 or 40 MHz. Argon gas flowing through the burner is ignited using a Tesla block, which creates a short discharge arc in an argon stream to initiate the ionization process. As soon as the plasma is lit, the Tesla block turns off.
The role of gas
Argon gas is ionized in a strong electromagnetic field and flows through a special rotationally symmetric sample in the direction of the magnetic field of the RF coil. Inelastic collisions created between neutral argon atoms and charged particles generate a stable high-temperature plasma of about 7000 K.
A peristaltic pump delivers an aqueous or organic sample to an analytical nebulizer, where it is converted into fog and injected directly into the plasma flame. The sample immediately collides with electrons and charged ions in the plasma and decays itself into the latter. Different molecules are divided into their respective atoms, which then lose electrons and recombine many times in the plasma, emitting radiation at the characteristic wavelengths of the participating elements.
In some designs, shear gas, usually nitrogen or dry compressed air, is used to “cut” the plasma at a specific location. One or two transmission lenses are then used to focus the emitted light on a diffraction grating, where it is divided into its component wavelengths in an optical spectrometer.
In other designs, the plasma falls directly onto the optical interface, which consists of a hole from which a constant stream of argon leaves, deflecting it and providing cooling. This allows the emitted light from the plasma to penetrate into the optical camera.
Some designs use optical fibers to transmit part of the light to individual optical cameras.
Optical camera
In it, after the separation of light into its various wavelengths (colors), the intensity is measured using a photomultiplier or tubes physically located to "view" a specific length (wavelengths) for each involved line of elements.
In more modern devices, the separated colors fall on an array of semiconductor photodetectors such as charge coupled devices (CCDs). In units using these detector matrices, the intensities of all wavelengths (within the system range) can be measured simultaneously, which allows the tool to analyze each element to which the unit is currently sensitive. Thus, samples can be analyzed very quickly using atomic emission spectroscopy.
Further work
Then, after all of the above, the intensity of each line is compared with previously measured known concentrations of the elements, and then their accumulation is calculated by interpolation along the calibration lines.
In addition, special software usually corrects interference caused by the presence of various elements in a given sample matrix.
Examples of the use of ICP-AES include the determination of metals in wine, arsenic in foods and trace elements associated with proteins.
ICP-OES is widely used in mineral processing to provide data on varieties of various streams, to build weights.
In 2008, this method was used at the University of Liverpool to demonstrate that the Chi Ro amulet, found at the Shepton Mallet and previously considered one of the earliest evidence of Christianity in England, dates from only the nineteenth century.
Appointment
ICP-AES is often used to analyze trace elements in soil, and for this reason it is used in a forensic examination to determine the origin of soil samples found at the crime scene or in victims, etc. Although the soil evidence may not be the only one in court, it certainly reinforces other evidence.
It is also quickly becoming the analytical method of choice for determining nutrient levels in agricultural soils. This information is then used to calculate the amount of fertilizer needed to maximize yield and quality.
ICP-AES is also used for engine oil analysis. The result shows how the engine works. Parts that wear out will leave marks in the oil that can be detected using ICP-AES. An ICP-AES analysis can help determine if parts are working.
In addition, he is able to determine how many oil additives remain, and, therefore, indicate how long he has a service life. Oil analysis is often used by fleet managers or car enthusiasts who are interested in learning as much as possible about the operation of their engine.
ICP-AES is also used in the manufacture of motor oils (and other lubricants) to control quality and to meet production and industry specifications.
Another type of atomic spectroscopy
Atomic absorption spectroscopy (AAS) is a spectroanalytical procedure for the quantitative determination of chemical elements using the absorption of optical radiation (light) by free atoms in a gaseous state. It is based on the absorption of light by free metal ions.
In analytical chemistry, the method is used to determine the concentration of a specific element (analyte) in the analyzed sample. AAS can be used to determine more than 70 different elements in solution or directly in solid samples by electrothermal evaporation, and is used in pharmacological, biophysical and toxicological studies.
Atomic absorption spectroscopy was first used as an analytical method at the beginning of the 19th century, and the fundamental principles were established in the second half by Robert Wilhelm Bunsen and Gustav Robert Kirchhoff, professors of the University of Heidelberg, Germany.
History
The modern form of AAS was largely developed in the 1950s by a group of Australian chemists. They were led by Sir Alan Walsh of the Commonwealth Scientific and Industrial Research Organization (CSIRO), Department of Chemical Physics, in Melbourne, Australia.
Atomic absorption spectrometry has many uses in various fields of chemistry, such as the clinical analysis of metals in biological fluids and tissues, such as whole blood, plasma, urine, saliva, brain tissue, liver, hair, muscle tissue, sperm, in some pharmaceutical processes production: the smallest amount of catalyst remaining in the final medicinal product, and analysis of water for metal content.
Scheme of work
The technique uses the atomic absorption spectrum of a sample to estimate the concentration of certain analytes in it. It requires standards with a known content of constituents in order to establish a connection between the measured absorption and their concentration, and therefore is based on the Bera-Lambert law. The basic principles of atomic emission spectroscopy are exactly as listed above in the article.
In short, the electrons of atoms in an atomizer can be transferred to higher orbitals (excited state) in a short period of time (nanoseconds), absorbing a certain amount of energy (radiation of a given wavelength).
This absorption parameter is specific for a particular electronic transition in a particular element. As a rule, each wavelength corresponds to only one element, and the width of the absorption line is only a few picometers (pm), which gives the technique elemental selectivity. The atomic emission spectroscopy scheme is very similar to this.