ATOMIC ABSORPTION SPECTROSCOPY
Atomic Absorption Spectroscopy (AAS) is a powerful analytical technique widely used in
chemistry to determine the concentration of metal elements in a sample.
principle:
1.Unique Atomic Spectra
Every element has a distinct arrangement of electrons. When electrons move
between specific energy levels, they absorb or emit light at exact wavelengths unique
to that element.
Think of it like a fingerprint: sodium always absorbs and emits at certain yellow
wavelengths, calcium at certain orange/red ones, etc.
This uniqueness lets us identify and measure one element even in a mixture.
2.Ground-State Absorption
In Atomic Absorption Spectroscopy, the sample is converted into free atoms in
their lowest energy (ground) state—for example, by heating in a flame or graphite
furnace.
A lamp that emits the element’s specific wavelength shines through this atomic
vapor.
If the vapor contains that element, its atoms absorb exactly that wavelength of
light.
The more atoms present, the more light is absorbed.
3.Beer–Lambert Law
The relationship between absorbed light and concentration is expressed by:
A = log10 ( 0) =
A (Absorbance): How much light is absorbed (a dimensionless number).
I₀: Intensity of the light before it enters the atomic vapor.
I: Intensity after passing through the vapor.
ε (Molar Absorptivity): A constant describing how strongly the atoms absorb at
that wavelength.
b (Path Length): The distance the light travels through the vapor (often fixed by
the instrument design).
c (Concentration): The amount of the analyte in the sample.
4.1.Radiation Source
, Hollow Cathode Lamp (HCL)
Purpose: Provides the exact wavelength of light that the target element can absorb.
Construction: A small, sealed glass tube filled with a low-pressure inert gas such as neon
or argon. The cathode is made from (or coated with) the metal you want to measure—
e.g., a copper cathode for copper analysis.
Operation: A voltage is applied across the electrodes. The inert gas becomes ionized, and
the ions bombard the cathode. This knocks atoms of the cathode metal into the gas
phase, where they emit their characteristic sharp spectral lines as they return to a lower
energy state.
Why it matters: Those sharp lines match the absorption lines of the same element in
your sample, ensuring high specificity.
Electrodeless Discharge Lamp (EDL)
Used when the element of interest gives off very weak light or when a stronger lamp
output is needed (for example, for selenium or arsenic).
Contains a small amount of the element in a quartz bulb and is excited by a radio-
frequency field instead of a normal electrical discharge, which produces a more intense
signal.
Atomic Absorption Spectroscopy (AAS) is a powerful analytical technique widely used in
chemistry to determine the concentration of metal elements in a sample.
principle:
1.Unique Atomic Spectra
Every element has a distinct arrangement of electrons. When electrons move
between specific energy levels, they absorb or emit light at exact wavelengths unique
to that element.
Think of it like a fingerprint: sodium always absorbs and emits at certain yellow
wavelengths, calcium at certain orange/red ones, etc.
This uniqueness lets us identify and measure one element even in a mixture.
2.Ground-State Absorption
In Atomic Absorption Spectroscopy, the sample is converted into free atoms in
their lowest energy (ground) state—for example, by heating in a flame or graphite
furnace.
A lamp that emits the element’s specific wavelength shines through this atomic
vapor.
If the vapor contains that element, its atoms absorb exactly that wavelength of
light.
The more atoms present, the more light is absorbed.
3.Beer–Lambert Law
The relationship between absorbed light and concentration is expressed by:
A = log10 ( 0) =
A (Absorbance): How much light is absorbed (a dimensionless number).
I₀: Intensity of the light before it enters the atomic vapor.
I: Intensity after passing through the vapor.
ε (Molar Absorptivity): A constant describing how strongly the atoms absorb at
that wavelength.
b (Path Length): The distance the light travels through the vapor (often fixed by
the instrument design).
c (Concentration): The amount of the analyte in the sample.
4.1.Radiation Source
, Hollow Cathode Lamp (HCL)
Purpose: Provides the exact wavelength of light that the target element can absorb.
Construction: A small, sealed glass tube filled with a low-pressure inert gas such as neon
or argon. The cathode is made from (or coated with) the metal you want to measure—
e.g., a copper cathode for copper analysis.
Operation: A voltage is applied across the electrodes. The inert gas becomes ionized, and
the ions bombard the cathode. This knocks atoms of the cathode metal into the gas
phase, where they emit their characteristic sharp spectral lines as they return to a lower
energy state.
Why it matters: Those sharp lines match the absorption lines of the same element in
your sample, ensuring high specificity.
Electrodeless Discharge Lamp (EDL)
Used when the element of interest gives off very weak light or when a stronger lamp
output is needed (for example, for selenium or arsenic).
Contains a small amount of the element in a quartz bulb and is excited by a radio-
frequency field instead of a normal electrical discharge, which produces a more intense
signal.
