Atomic Absorption Spectroscopy (AAS) instrumentation consists of several components that work together to detect and quantify the concentration of specific metallic elements in a sample.
Here's a brief overview of the main components:
1. Source (Hollow Cathode Lamp or Electrodeless Discharge Lamp):
A) Hollow Cathode Lamp (HCL):
Most common source in AAS, it emits radiation of a specific element.
The lamp contains an anode and a cathode made of the metal of interest.
When a current is passed, metal ions are produced, which then emit characteristic radiation when they return to the ground state.
B) Electrodeless Discharge Lamp (EDL):
Used for elements that are difficult to analyze using HCL.
It contains the element of interest in gaseous form, and radiation is emitted when the gas is excited by microwave or radiofrequency energy.
2. Atomizer (Flame or Graphite Furnace):
A) Flame Atomizer:
Sample solution is nebulized to create a fine mist.
This mist is then introduced into a flame, where it is atomized.
The most common fuels used are acetylene and air, but other mixtures like acetylene and nitrous oxide can be used.
B) Graphite Furnace Atomizer:
Small volumes of the sample are introduced into a graphite tube, which is then electrically heated in stages to dry the sample, ash organic matter, and atomize the analyte.
3. Monochromator:
Separates the wavelengths of light so that only the specific wavelength of interest (corresponding to the analyte's absorption) reaches the detector.
It helps in isolating the desired radiation and eliminates any unwanted radiation.
4. Detector:
Typically, a photomultiplier tube (PMT), it converts the transmitted light from the sample into an electrical signal.
The decrease in light intensity due to absorption by the atoms is measured and related to the concentration of the analyte.
5. Output Device (Data Handling System):
Converts the electrical signal from the detector into a form suitable for interpretation, such as a digital readout or a graph.
Modern AAS instruments are usually connected to computers, facilitating data storage, manipulation, and analysis.
6. Flame Control System (For flame AAS):
Regulates the flow of gases (fuel and oxidant) to maintain a stable and consistent flame.
In a typical AAS procedure, the source emits light of a specific wavelength corresponding to the element being analyzed. This light passes through the atomized sample.
The atoms in the sample will absorb a portion of this light.
The monochromator then isolates the specific wavelength of light absorbed by the sample, which is then detected by the PMT.
The reduction in light intensity corresponds to the concentration of the element in the sample.