Atomic Absorption Spectroscopy for B.Sc. Biotechnology

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1. 1
Atomic Absorption Spectroscopy (AAS)

Introduction
• Atomic Absorption Spectroscopy (AAS) is an analytical technique used to determine
the concentration of elements (mainly metals) in a sample.
• It is based on the absorption of light by free (ground-state) atoms in the gaseous state.
• AAS is highly specific, sensitive, and accurate for detecting trace elements.

2. 2
Instrumentation of AAS
1. Radiation Source
• Commonly a Hollow Cathode Lamp (HCL) specific to the element.
• Emits sharp line spectra for accurate detection.
2. Atomizer
• Converts sample into free atoms.
• Types:
o Flame Atomizer: Uses a flame (Air-Acetylene or N2O-Acetylene).
o Graphite Furnace Atomizer (Electrothermal AAS): More sensitive; uses high
temperatures.
3. Monochromator
• Selects the specific wavelength of interest.
• Removes unwanted wavelengths.
4. Detector
• Usually a Photomultiplier Tube (PMT).

3. 3
• Converts light signal into an electrical signal.
5. Readout Device
• Displays the absorbance or concentration.
• Can be digital or chart-based.

Types of Atomic Absorption Spectroscopy
Type Description Application
Flame AAS Uses flame for atomization Moderate sensitivity
Graphite Furnace AAS
(GFAAS)
Uses furnace; no flame High sensitivity; small sample
Hydride Generation AAS
For volatile hydrides (As,
Se, Sb)
Specialized detection
Cold Vapor AAS Used for Hg (Mercury)
Mercury analysis in water and
biological samples

Calibration and Quantification
• Standard Solutions of known concentration are used.
• A calibration curve is plotted (Absorbance vs Concentration).
• The unknown sample's concentration is obtained by comparing its absorbance with the
curve.

Sample Preparation
• Liquid samples: Directly aspirated.
• Solid samples: Digested using acids to form a solution.
• Biological/Environmental samples may require wet digestion or dry ashing.

Advantages of AAS
• High sensitivity and selectivity.
• Can detect ppb (parts per billion) level.

4. 4
• Requires small sample volume.
• Relatively fast analysis.
• Widely used in quality control and research.

Limitations
• Only metallic elements can be detected.
• Each element requires a separate lamp.
• Matrix interferences (physical/chemical) may affect accuracy.
• Flame AAS has lower sensitivity than furnace AAS.

Applications of AAS
Field Application
Environmental Science Detection of heavy metals in water, soil
Clinical/Medical Trace elements in blood, urine
Food Industry Metal contamination in food
Pharmaceuticals Quality control of raw materials
Geology Metal analysis in ores and minerals
Forensic Science Gunshot residue, toxicology

Important Points to Remember
• AAS measures absorbance not emission (unlike AES).
• Flame AAS is less sensitive than Graphite Furnace AAS.
• Monochromators isolate the analytical wavelength.
• Sample must be in solution form for analysis.
• Background correction techniques (like D2 lamp or Zeeman correction) are used to
remove interferences.

Conclusion
Atomic Absorption Spectroscopy is a powerful tool in modern analytical chemistry for detecting
and quantifying trace metals. Its precision, simplicity, and low detection limits make it
invaluable in many scientific and industrial fields