Atomic optical spectrometry

Atomic spectrometry, sometimes called atomic spectroscopy or optical atomic spectrometry, is a set of tools for analytical chemistry that involves the measurement of light produced by the interaction of photons with the atoms of chemical elements. It is based on the properties of electrons at different energy levels within electrons, and the properties that cause light, of a charateristic wavelength, to be absorbed in moving an electron to a more energetic level, or to be emitted when electrons decay to a less energetic energy level.

There are three broad types of atomic spectrometry:

• Atomic absorption spectrometry
• Atomic emission spectrometry
• Atomic fluorescence spectrometry

Each have advantages and disadvantages, which must be judged in specific applications. That a particular method, for example, is good at the simultaneous analysis of multiple elements is a benefit for geological or forensic laboratories trying to identify specimens, but not especially important for clinical chemists that simply want to know the potassium or sodium level in a blood sample.

As with other techniques of analytical chemistry, one method or variant may displace another, but improvements in a displaced method may create a new and constructive competition. For example, neutron activation analysis also does elemental analysis, but on nuclei rather than electrons. In its basic form, it has the restriction of needing access to a nuclear reactor.

Atomic emission spectrometry

Analyte atoms in solution are aspirated into the excitation region where they are desolvated, vaporized, and atomized by a flame, discharge, or plasma. These high-temperature atomization sources provide sufficient energy to promote the atoms into high energy levels. The atoms decay back to lower levels by emitting light. Since the transitions are between distinct atomic energy levels, the emission lines in the spectra are narrow. The spectra of samples containing many elements can be very congested, and spectral separation of nearby atomic transitions requires a high-resolution spectrometer. Since all atoms in a sample are excited simultaneously, they can be detected simultaneously using a polychromator with multiple detectors. This ability to simultaneously measure multiple elements is a major advantage of AES compared to atomic absorption spectroscopy.

Excitation sources

Excitation sources include:

• Direct-current plasma (DCP)
• Flame
• Inductively-coupled plasma (ICP)
• Laser-induced breakdown (LIBS)
• Laser-induced plasma
• Microwave-induced plasma (MIP)
• Spark or arc