- Spectroscopy:
- The science of the interaction of energy, in the form of electromagentic radiation, acoustic waves, and particle beams, with matter.
- Spectrometry:
- The measurement of the intensity of radiation with some electronic device.
- Spectrometer:
- An instrument that can measure radiation intensity as a function of wavelength (or wavenumber or photon energy).
- Spectrophotometer:
- A spectrometer that uses a photon detector to measure the ratio of the radiant power incident on (P0) and emergent from (P) a sample of matter.
Atomic spectroscopy exploits different energetic transitions experienced by atoms that are generally associated with either the absorption or emission of photons. When these transitions involve the excitation and relaxation of the valence (outer or bonding) shell electrons of metal atoms and ions, the corresonding photons have energies within the ultraviolet and visible regions of the spectrum.
In atomic absorption spectrophotometry (AAS), absorption of a photon results in excitation of an electron from a lower to higher energy atomic orbital (AO). The instrument measures the absorbance, A, which is defined as the logarithm of the ratio of incident to transmitted radiant power of the photon beam, A = log(P0 ÷ P).
In atomic emission spectrometry (AES), thermal or electrical energy from an arc, flame, spark, or plasma is used to excite and electron from a lower to higher energy AO; when the excited electron returns to its original AO (i.e. the ground state), it may do so by emitting a photon. The instrument measures the intensity, I, of these emitted photons as a function of wavelength.
Because AO energies are well-defined, atomic absorption and emission spectra consist of discrete, narrow lines. This allows the concentration of metallic elements in different samples to be determined selectively, with lower limits at or below 1 mg/L (1 ppm). Techniques such as graphite furnace atomic absorption spectrophotometry (GFAAS) allow concentration to be measured down to µg/L (ppb) levels. Actual limits-of-detection vary with both element, technique, and sample matrix.