Atomic Absorption Spectroscopy (AAS) is a powerful analytical technique used to determine the concentration of specific elements within a sample by measuring the amount of light absorbed by free atoms. In this method, the sample is first atomised—converted into gaseous atoms—after which light from an element-specific hollow cathode lamp passes through the vapour. The extent […]
Atomic Absorption Spectroscopy (AAS) is a powerful analytical technique used to determine the concentration of specific elements within a sample by measuring the amount of light absorbed by free atoms.
In this method, the sample is first atomised—converted into gaseous atoms—after which light from an element-specific hollow cathode lamp passes through the vapour. The extent of light absorption is directly proportional to the concentration of the element, in accordance with the Beer–Lambert Law. Renowned for its high sensitivity, precision, and selectivity, AAS is extensively applied across diverse fields such as environmental monitoring, food and agricultural analysis, clinical and pharmaceutical testing, and material quality control to accurately quantify trace and major metal elements.
Atomic Absorption Spectroscopy (AAS) is an analytical technique used to determine the concentration of metallic elements in a sample.
It is based on the absorption of light by free atoms in the gaseous state. Each element absorbs light at specific wavelengths, allowing for selective and quantitative analysis of metals such as copper, zinc, lead, calcium, and even precious metals like gold and rhodium.
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The principle of AAS is grounded in the concept that atoms absorb light energy of a characteristic wavelength. When a solution containing metal ions is aspirated into a flame or graphite furnace, the metal ions are atomized (converted into free atoms).
When monochromatic light from a hollow cathode lamp (specific to that element) passes through these atoms, a portion of the light is absorbed. The amount of light absorbed is directly proportional to the concentration of the element in the sample.
Key principle equation (Beer–Lambert’s law):
A = k . c
Where:
There are two main types of AAS methods based on the atomization technique:
| Type | Description | Application |
|---|---|---|
| Flame AAS (FAAS) | The sample is injected into a graphite tube, which is electrically heated to vaporise and atomize the sample. | Suitable for higher concentration ranges (ppm level). |
| Graphite Furnace AAS (GFAAS) | The sample is injected into a graphite tube, which is electrically heated to vaporise and atomise the sample. | Suitable for trace analysis (ppb level). |
The output of an AAS instrument is a calibration curve or absorbance reading at a specific wavelength.
| Component | Function |
|---|---|
| Radiation Source (Hollow Cathode Lamp) | Emits element-specific radiation. |
| Converts a sample into free atoms. | Converts sample into free atoms. |
| Monochromator | Isolates the specific wavelength absorbed by the atoms. |
| Detector (Photomultiplier Tube) | Measures the intensity of unabsorbed light. |
| Signal Processor/Readout | Converts the detected signal into absorbance or concentration. |
| Nebuliser & Spray Chamber | Converts a liquid sample into a fine aerosol for atomization. |
AAS finds applications across scientific, industrial, and environmental domains:
| Advantages | Limitations |
|---|---|
| Highly sensitive and selective for metal ions. | Limited to metallic elements — cannot analyze non-metals. |
| Requires small sample volume. | Requires a small sample volume. |
| Simple operation and low maintenance cost. | Matrix interferences can affect accuracy. |
| Provides quantitative and trace-level analysis. | Flame AAS has lower sensitivity than Graphite Furnace AAS. |
| Fast and reproducible results. | Requires careful sample preparation to avoid contamination. |
| Parameter | Atomic Absorption Spectrum (AAS) | Atomic Emission Spectrum (AES) |
|---|---|---|
| Energy Source | External light source (Hollow Cathode Lamp). | Atoms themselves emit light when excited. |
| Process | Measures light absorbed by ground-state atoms. | Measures light emitted by excited atoms. |
| Signal Relation | Absorbance ∝ Concentration. | Emission intensity ∝ Concentration. |
| Flame Requirement | May use low to moderate flame temperature. | Requires high-temperature plasma or flame. |
| Example | Flame or Graphite Furnace AAS. | Inductively Coupled Plasma (ICP-AES). |
AAS relies on atomization and electronic transitions of free metal atoms in the ground state.
| Parameter | AAS | AFS |
|---|---|---|
| Measurement | Measures absorption of light by ground-state atoms. | Measures fluorescence (reemission) of light by excited atoms. |
| Sensitivity | High for most metals. | Even higher sensitivity for certain elements (e.g., Hg, As, Se). |
| Light Source | Hollow cathode lamp or EDL. | Same as AAS, but emission detected at right angle. |
| Interferences | More prone to matrix interferences. | Less interference due to emission measurement. |
| Applications | Quantitative metal analysis. | Ultra-trace analysis and environmental monitoring. |
Atomic Absorption Spectroscopy remains a cornerstone of analytical chemistry, offering high precision, accuracy, and reliability for metal quantification. From environmental pollution control to jewellery quality assessment, AAS continues to be indispensable in both research and industry.
Whether analysing trace metals in water or determining gold purity, AAS provides a dependable path to precise, reproducible results.
AAS is used to determine the concentration of metals and metalloids in various samples such as water, food, soil, biological fluids, and industrial materials.
AAS works on the principle that free atoms absorb light of a specific wavelength. The amount of light absorbed is proportional to the concentration of that element in the sample.
es. AAS is based on the Beer–Lambert Law, which states that absorbance is directly proportional to the concentration of the absorbing species and the path length of light through the sample.
In the AAS method, the sample is atomized (converted into free atoms) using a flame or graphite furnace. A light beam from an element-specific lamp passes through the atomised sample, and the absorbed light intensity is measured to determine the element’s concentration.
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