Atomic Absorption Spectroscopy (AAS) works by measuring the absorption of light by free atoms in the gaseous state to determine the concentration of an analyte in a sample. Here's a detailed breakdown:
AAS Working Principle
The process involves several key steps:
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Atomization: This is where the sample is converted into free atoms in the gaseous phase. According to the reference text, this is achieved using a heat source, commonly a flame, to create a steady state of freely dissociated ground state atoms.
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Light Source: A specific wavelength of light is passed through the atomized sample. This light source is usually a hollow cathode lamp (HCL) that emits light at a wavelength specific to the element being analyzed.
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Absorption: When the light passes through the flame containing the atoms, atoms of the element of interest will absorb light at their specific wavelengths. The amount of light absorbed is proportional to the concentration of the element in the sample.
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Detection: A detector measures the amount of light that passes through the flame without being absorbed. By comparing the intensity of light before and after passing through the flame, the spectrometer determines the absorbance.
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Quantification: The absorbance is then correlated to the concentration of the analyte using a calibration curve.
Simplified Summary Table
| Step | Description | Method/Tools Used |
|---|---|---|
| Atomization | Converting the sample into free, ground-state atoms. | Flame (heat source) |
| Light Emission | Passing a specific wavelength of light through the atomized sample. | Hollow Cathode Lamp (HCL) |
| Absorption | Atoms absorb light at specific wavelengths. | Atoms in the flame |
| Detection | Measuring the intensity of light that didn't get absorbed. | Detector |
| Quantification | Correlating absorbance to the concentration of the analyte using a calibration curve. | Spectrometer Software, Calibration |
Example Scenario
Imagine you're analyzing a water sample for lead (Pb) contamination.
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Preparation: You aspirate the water sample into the AAS.
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Atomization: The sample goes into the flame, and any lead compounds are broken down into individual lead atoms.
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Light Source: A hollow cathode lamp containing lead emits light at the characteristic wavelength of lead (e.g., 283.3 nm).
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Absorption: Lead atoms in the flame absorb some of this 283.3 nm light.
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Detection & Quantification: The detector measures the light intensity, calculates the absorbance, and, using a calibration curve, determines the lead concentration in your water sample.
