Atomic spectroscopy is a vital tool in elemental analysis, both qualitatively and quantitatively. It can be broadly divided into optical spectroscopy, mass spectroscopy, and X-ray spectroscopy methods. The optical spectroscopic methods are atomic absorption spectroscopy (AAS), atomic emission spectroscopy (AES), and atomic fluorescence spectroscopy (AFS). The first step in all three methods is atomization, where the solid, liquid, or solution-phase samples are converted into gas-phase atoms and ions.
In AAS, the gaseous samples interact with electromagnetic radiation and absorb photons with the exact energies that promote electrons of ground-state atoms to their excited states. For example, the unpaired 3s electron of the Na atom gets promoted to the 3p, 4p, or 5p orbital on the absorption of radiation of 285 nm, 330 nm, or 590 nm, respectively. The reduction in transmitted light of certain wavelengths is measured by the detector and visualized with an absorbance or transmittance spectrum.
In AES, the gas-phase atoms in the ground state are electronically excited with heat or electrical discharge energy. These short-lived, high-energy excited gas-phase atoms relax back to the ground state, emitting photons corresponding to the energy gap. The intensity of the emitted light is detected and converted to an electrical signal that gives a fingerprint of the sample. For instance, electronic transitions of excited Na atoms from the 3p, 4p, and 5p orbitals back to the 3s orbital result in emissions around 590 nm, 330 nm, and 285 nm, respectively. The emitted radiation is measured and processed into a spectrum.
In AFS, the ground-state gas-phase atoms are irradiated by a characteristic wavelength and promoted to the electronically excited state. Provided radiationless transition does not occur, the excited-state atoms relax to the ground state by fluorescing at the exact wavelength corresponding to the energy they absorbed. The detector is usually at a right angle to the source beam, where only fluorescence emissions should reach it.
Unlike molecular spectra, atomic spectra have sharp lines due to the absence of various rotational and vibrational energy states that lead to peak broadening in molecular spectra.
Atomic spectroscopy is an analytical tool for qualitative and quantitative elemental analysis.
The main types include atomic absorption spectroscopy, or AAS; atomic emission spectroscopy, or AES; and atomic fluorescence spectroscopy, or AFS.
All three methods begin with atomization, which is the critical step of breaking down liquid samples into gas-phase atoms.
In AAS, hot gaseous samples irradiated with a range of electromagnetic radiation absorb light of the specific wavelengths that cause electronic transitions in the atoms to higher-energy orbitals.
The amount of light transmitted at each wavelength is measured by the detector.
In AES, the input of heat or electrical discharge on the ground-state gaseous atoms causes electronic excitation.
These high-energy atoms quickly return to the ground state, emitting photons that match the energy differences.
In AFS, the ground-state gaseous atoms are irradiated at a characteristic wavelength for promotion of a specific atom to the excited state.
If the atom is present, it fluoresces, which is measured by a detector placed at a right angle to the laser beam.
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