Atomic absorption spectroscopy

BY- K. Sai Manogna (MSIWM014)

Atomic absorption spectroscopy (AAS) is a method in analytical chemistry for determining the concentration of a specific metal element in a sample. The process can be used in a solution to analyze the concentration of over 70 different metals. While atomic absorption spectroscopy dates from the nineteenth century, a team of Australian chemists primarily developed the modern form during the 1950s. They were headed by Alan Walsh and served in the Chemical Physics Division of the CSIRO (Commonwealth Science and Industry Research Organisation) in Melbourne, Australia. 

By applying characteristic wavelengths of electromagnetic radiation from a light source, atomic absorption spectrometry detects elements in either liquid or solid samples. Wavelengths can be absorbed differently by individual components, and these absorbances are calculated against expectations. In effect, AAS takes advantage of the various wavelengths of radiation that different atoms absorb. In AAS, analytes are first atomized so that their characteristic wavelengths are emitted and registered. When those atoms consume particular energy during excitation, electrons go up one energy level in their respective atoms. 

These atoms emit energy in the form of light as electrons return to their original energy state. There is a wavelength of this light that is characteristic of the element. According to the light wavelength and intensity, relevant elements can be detected, and their concentrations determined according to the light wavelength. 


The approach uses absorption spectrometry to determine an analyte’s concentration in a sample. Thus it relies heavily on the Beer-Lambert rule. In short, by consuming a given amount of energy, the atoms’ electrons in the atomizer can be promoted to higher orbitals for a short period. This quantity of energy is unique to a specific transformation of electrons in a particular element, and each wavelength corresponds to only one element in general. This gives its elemental selectivity to the process. 

Since the amount of energy placed into the flame is known and it is possible to calculate the amount remaining on the other side of the detector, it is possible to estimate from the Beer-Lambert law how many of these transitions have occurred and thus obtain a signal proportional to the concentration of the measured product.

The Instrumentation 

There are four components of the standard AAS instrument: the sample introduction region, the source of light (radiation), the monochromator or polychromator, and the detector. 

It needs to be atomized in order to test a sample for its atomic constituents. The light could then illuminate the sample. Finally, the light emitted is measured through a detector. A spectrometer is usually used between the atomizer and the detector to minimize the effect of the atomizer’s emission (e.g., black body radiation) or from the atmosphere. 

Types of Atomizer:

Usually, the method uses a flame to atomize the sample, but other atomizers are also used, such as a graphite furnace or plasmas, particularly inductively coupled plasmas. 

It is side-long (usually 10 cm) and not deep when a flame is used. The flame’s height above the burner head can be adjusted by changing the fuel mixture’s flow. At its longest axis (the lateral axis), a ray of light passes through this flame and reaches a detector. 

Liquid analysis 

A liquid sample is usually converted in three stages into an atomic gas: 

1. The liquid solvent is evaporated (Drying), and the dry sample remains 

2. Vaporization (Ashing)-the solid specimen vaporizes into a gas 

3. Atomization is divided into free atoms by the compounds that make up the sample. 

Sources of Radiation 

The chosen radiation source has a narrower spectral range than that of the atomic transitions. 

Cathode Hollow Lamps 

The most common source of radiation in atomic absorption spectroscopy is hollow cathode lamps. A cylindrical metal cathode holding the metal for excitation and an anode is inside the lamp, filled with argon or neon gas. Gas particles are ionized when a high voltage is applied to the anode and cathode. Gaseous ions gain sufficient energy to eject metal atoms from the cathode as the voltage increases. Some of these atoms are excited, releasing light with the characteristic frequency of the metal. Various modern hollow cathode lamps are selective for several metals. 

Lasers with diodes 

Lasers, especially diode lasers because of their strong properties for laser absorption spectrometry, can also conduct atomic absorption spectroscopy. The method is then either referred to as diode laser atomic absorption spectrometry (DLAAS or DLAS) or, since wavelength modulation is most commonly used, spectrometry of absorption of wavelength modulation. 

Context Methods of Correction:

The spectral overlap is unusual due to the limited bandwidth of hollow cathode lamps. That is, an absorption line from one element is unlikely to overlap with another. Molecular emissions are much larger, so a specific molecular absorption band is more likely to overlap with an atomic line. This can lead to artificially high absorption and an improperly high measurement of the solution concentration. In order to correct this, three methods are usually used: 

Zeeman correction: A magnetic field is used to break the atomic line into two sidebands. To still overlap with molecular bands, these sidebands are close enough to the initial wavelength, but far enough, they do not overlap with the atomic bonds. It is possible to equate the absorption in the presence and absence of a magnetic field, the difference being the absorption of interest atomically. 

Correction to Smith-Hieftje: This was invented by Stanley B. Smith and Gary M. Hieftje. The high current pulses the hollow cathode lamp, creating more significant atoms and self-absorption population during the pulses. This self-absorption allows the line to be broadened, and the line intensity decreases at the original wavelength. 

Deuterium lamp correction: In this case, for the calculation of background emissions, a different source known as a broad-emission deuterium lamp is used. The use of a specific lamp makes this method the least reliable, but this method is most widely used because of its relative simplicity and the fact that it is the oldest of the three.

Advantages of AAS are given below: 

  1. Strong throughput of samples 
  2. Simple to make use of 
  3. High accuracy 
  4. Inexpensive methodology 

Disadvantages/drawbacks of AAS are as follows: 

  1. It is only possible to evaluate solutions. 
  2. Less sensitivity compared to the furnace with graphite 
  3. Relatively large quantities of samples are needed (1-3 ml) 
  4. Difficulties with refractory components



Atomic absorption spectroscopy has proven to be the most powerful method in the use of liquid-density implants since it was introduced by Alan Walsh in the mid-1950s.

More than 60 -70 items including the rarest earth metals determined by this method in the focus from tracking to large numbers. The direct use of this process is limited to instruments other than B, Si, As, Se & Te.

Several non-ferrous metals are weighed with indirect metals. Since atomic spectroscopy does not require sample correction it is an appropriate non-chemical tool as well.

Some elements, especially metals, play a vital role in biological processes, whether they are simple cofactors in enzymes, the atom in the macromolecule of living organisms such as iron in hemoglobin or magnesium in chlorophyll, or as toxins that affect the body.

The use of atomic spectroscopy will make important data available in understanding the biological roles of these substances.

In general, molecules enlarge the band spectra and atoms provide a clearly defined line of line. So, in atomic spectroscopy, the line spectra are studied. These lines are seen visually as light, corresponding to a certain length of the boundaries, which are the atomic emission rays or black lines against the luminous background, which is the atomic absorbing spectra.

On the surface of the element, the wavelength at which the absorption or discharge is detected is associated with changes in which a small change in energy occurs. In general, the appearance of a number of cells, the concentration of atoms is not measured directly in solution but is converted into free atoms.

The process of converting an analyte into a solid, liquid form, or solution into a free gas atom is called atomization. Atoms that are volatilized can be flame or electro thermally in the oven.

In this case, the elements will easily penetrate or emit monochromatic radiation at the right distance. Usually nebulizers (atomizers) are used to spray a standard solution or test in the flame where light is transmitted. Alternatively, the light beam is transferred, to the oven, through a hole containing the inspired apparatus.


The volatilization of molecules in the sun produces free atoms. These free atoms are happy when light of a certain length is able to emit spectral lines corresponding to the energy required for the electronic transition from the earth’s state to a happy state, allowed to pass through flame. The atomic spectra obtained is fully determined by the object involved and the amount of light concentrated is equal to the number of atoms in the path of light. Therefore, in addition to granting ownership of the material in the sample, this process of viewing and providing information on the quantity of the material.


For all types of atom-absorbing spectrometer, the following components are required:

Radiation source:

The source should be such that it emits strong rays of the element to be determined, usually the resonance line of the object. It is almost impossible to separate the maximum length of resonance from a continuous source using a prism or diffraction grating or both at the same time. This problem was solved by the invention of empty cathode emission lamps. Such lamps emit monochromatic radiation element analyzes.

(a) Empty Cathode Lamp:

The cathode contains an empty cup in which the element will be cut. The anode is a tungsten wire. Both electrodes are inserted into a tube containing internal gas (argon or neon). The light window is constructed using quartz, silica or glass. The exact metal depends on the length of the scale to be transmitted. When a potential of approximately 3000V is used between these two electrodes, electrons trigger the immersion of gas into the lamp. These ions which receive enough energy to decompose atoms in the cathode, that is, explode other atoms of iron. These atoms regenerate and when they return to the ground, they begin to release the visible metal used to build the cathode (The light emitted spectrum corresponds to the elevation of the cathode emissions and the gas in the lamp. filling, and selection of very sharp spectral lines to obtain better sensitivity, without cases of disruption caused by other elements). The pressure stored in the lamp is 1 to 5 torr. Each blank cathode lamp emits a wide range of metal used in the cathode; this looks bad as a separate lamp should be used for each item to be analyzed. Another hollow cathode lamp is a wireless emission lamp (EDL) now made available for its light intensity of almost 10-100 times but not as stable as HCL (hollow cathode lamps). They are made of a closed quartz tube containing the salt of the substance and gas entering. The radio frequency field is used to cool the gas which makes the metal ionized. These lamps are usually reserved for items such as As, Hg, Sb, Bi and P.

Working of Atomic Absorption Spectrometer

Practically the meter is adjusted to learn zero absorption when spraying a blank solution in flame and the uninterrupted light of an empty cathode lamp passes through a photomultiplier tube. When a solution with a suction type is inserted then a portion of the light is applied which leads to a decrease in the intensity of the light which falls into the photomultiplier and produces a deviation from the meter needle. Standard object solutions are used to create a measuring curve where the content of the test solutions can be measured.


  • Used to determine the trace of a metal in a liquid.
  • Used in clinical laboratories for the removal of body fluids.
  • Estimation of soil and water samples.
  • Determination of lead in petrol.
  • Determination of metallic elements in food industry