Atomic absorption spectroscopy Is very similar to flame photometry with the difference that it measures the absorption of a beam of monochromatic light from the atoms in the fire. This technique was first introduced by Alan Walsh in Australia in 1954. We will examine the principle, instrumentation and software one by one. The fundamental principle behind the AAS is the free atoms normally stay in the ground state that are capable of absorbing the energy of their particular resonance wavelength. If light of the resonance wavelength is passed through the flame containing the atoms in sample, then part of this light will be absorbed. The atoms absorb UV or visible light and make the transitions to higher energy levels. The absorption will be directly proportional to the number of atoms in the ground state from the fire.
The significant gap in the instrumentation of atomic absorption spectroscopy and flame spectrophotometry is that the existence of a radiation source a specific resonance. Wavelength can’t be isolated from the constant source by means of a prism or diffraction gratings. Therefore, for this purpose, a hollow cathode lamp is utilized. Light Source: Hollow Cathode Discharge Lamp: It includes a tungsten anode and cathode as may be seen in the diagram on the right is a hollow cylindrical tube that is lined by the component to be determined. These are sealed in the glass tube filled with an inert gas such as neon or argon in a very low pressure. At the end of the cylinder is a window, composed of quartz or Pyrex, transparent to the emitted radiation. Each component in question will consequently emit monochromatic radiation characteristic of the emission spectrum of that specific element involved. So, each component has its own unique lamp that must be utilized for the analysis.
- Nebulizer: It Makes a fine spray of this Sample for the debut in the fire. The aerosol along with the fuel and oxidant are mixed thoroughly for the introduction to the fire.
- Atomizer: The components which needs to be Analysed should maintain the atomic state. Here comes the part of atomizer. It breaks down the molecules to the atoms by exposing the analyte to elevated temperatures in a fire of graphite furnace as explained in previous post,
- Monochromator: A monochromator is used to pick the particular wavelength of light that is absorbed by the sample and also to exclude other wavelengths. The choice of the specific wavelength enables the determination of this element.
- Detector: The mild chosen by the Monochromator is directed onto the sensor that typically is a photomultiplier tube which converts the light signal to electrical signal proportional to the light intensity.
It is highly sensitive technique and can measure up to parts per billion of a gram ugdm-3. It is used to detect the presence of metals as impurity or in metals. The minute levels of these metals can be detected in biological samples such as copper in the brain cells.