Atomic Absorption Spectroscopy (AAS) is an analytical technique used to determine the concentration of metallic elements in a sample. It relies on the principle that free atoms in the ground state can absorb light at specific wavelengths characteristic of each element.

Principle of AAS

1. A sample is atomized, converting the analyte into free, neutral atoms in the gas phase.
2. A hollow cathode lamp (HCL) emits light at a wavelength specific to the element being measured.
3. The free atoms absorb this light, and the reduction in intensity is measured by a detector.
4. The absorbance is proportional to the concentration of the element according to the Beer-Lambert Law.

Instrumentation

1. Hollow Cathode Lamp: Contains the same metal as the target analyte, emitting its characteristic line spectrum.
2. Atomizer: Flame (air-acetylene or nitrous oxide-acetylene) for liquid samples, or graphite furnace for trace analysis.
3. Monochromator: Isolates the specific wavelength of interest from other emission lines.
4. Photomultiplier Detector: Measures the intensity of transmitted light.

Atomization Techniques

1. Flame AAS (FAAS): The sample solution is aspirated into a flame where it is desolvated, atomized, and analyzed. Detection limits range from ppm to ppb.
2. Graphite Furnace AAS (GFAAS): A small sample volume is placed in a graphite tube, heated stepwise to atomization, achieving ppb to ppt detection limits.
3. Hydride Generation AAS: Used for elements like As, Se, and Hg, where volatile hydrides are formed and transported to the atomizer.

Interferences

1. Spectral Interferences: Overlapping absorption lines from other elements; corrected by using alternative wavelengths or background correction (Zeeman or deuterium lamp).
2. Chemical Interferences: Formation of refractory compounds that resist atomization; minimized by adding releasing agents (e.g., lanthanum for calcium).
3. Matrix Effects: Differences in viscosity and surface tension between standards and samples affect nebulization efficiency.

Applications

1. Environmental analysis of heavy metals (Pb, Cd, Hg, As) in water, soil, and air.
2. Clinical testing of trace elements (Fe, Cu, Zn, Mg) in blood and urine.
3. Food safety monitoring of toxic metals in agricultural products and seafood.
4. Quality control of metals in alloys, ores, and pharmaceutical raw materials.