Atomic spectroscopy

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Atomic spectroscopy (also called atomic spectrometry ) is a collective term for spectroscopic methods that are used for the quantitative and qualitative determination of chemical elements . Atomic spectroscopy is a sub-area of analytical chemistry . One differentiates:

Atomic Absorption Spectrometry (AAS)

Schematic structure of an F-AAS spectrometer

The atomic absorption spectrometry (AAS) is a proven and rapid method for quantitative and qualitative analysis of many elements ( metals , semi-metals ) in mostly aqueous solutions and solids. It is based on the attenuation ( absorption ) of radiation through interaction with free atoms. Since every chemical element has a characteristic line spectrum , statements about the elements contained in a sample can be made by evaluating the difference spectrum to a reference measurement without a sample. Atomic absorption spectrometry is divided into the following sub-processes with regard to the conversion of a sample into the gas phase:

  • F-AAS (short for flame atomic absorption spectrometry , dt. 'Flame atomic absorption spectrometry', also called flame technique or flame photometry)
  • GF-AAS or etA-AAS ( graphite furnace atomic absorption spectrometry , also called graphite furnace technology )
  • CV-AAS ( cold vapor atomic absorption spectrometry , dt. 'Atomic absorption spectrometry with cold vapor technique', also called hydride technique)
  • HR-CS AAS ( high-resolution continuum-source atomic absorption spectrometry )

Atomic Emission Spectrometry (AES)

The structure of an F-AES corresponds to that of an F-AAS without a hollow cathode lamp

The atomic emission spectrometry (AES), often optical emission spectrometry (OES) as the AAS for quantitative and qualitative analysis of solid, liquid and gaseous samples.

The method is based on the fact that an excited atom emits element-specific , electromagnetic radiation and thus provides information about the sample. The atoms are excited by an external supply of energy, e.g. B. via a flame, an arc, a spark or an inductively coupled plasma (ICP), and the transition to the plasma state . Therefore the following sub-procedures result:

A laboratory flame photometer
  • Flame atomic emission spectrophotometry (F-AES)
  • Optical emission spectrometry with inductively coupled plasma ( inductively coupled plasma optical emission spectrometry , ICP-OES)
  • Microwave plasma torch atomic emission spectrometry MPT-AES

Atomic Fluorescence Spectroscopy (AFS)

Both fluorescence and phosphorescence are forms of luminescence (cold glow). However, fluorescence is characterized by the fact that it ends quickly (usually within a millionth of a second) after the end of the irradiation. With phosphorescence, on the other hand, there is an afterglow that can last from fractions of a second to hours.

Atomic fluorescence is the optical emission of atoms brought into gas phase, which have been brought into a higher energy state by absorption of electromagnetic radiation (e.g. photons). The main advantage of fluorescence spectroscopy over AAS is its greater sensitivity, which is made possible by the lower background noise. The resonant excitation method offers a selective excitation of the analyte in order to avoid interference. The AFS enables an investigation of the electronic structure of the atoms and quantitative measurements. An analysis of solutions or solids requires that the analyte is dissolved, evaporated and atomized. This takes place in a heat pipe or in a flame or graphite furnace; it should be done at relatively low temperatures. The atoms are actually excited by a hollow cathode lamp (HKL) or a laser. The detection is similar to that of atomic emission spectroscopy using monochromators and photomultipliers.

Mass spectrometry with inductively coupled plasma (ICP-MS)

ICP-MS stands for inductively coupled plasma mass spectrometry , i.e. mass spectrometry using inductively coupled plasma. In contrast to the previous techniques, no light absorbed or emitted by atoms is observed in ICP-MS, but the impact of ions or their masses on a detector is measured.

A liquid sample is sucked in by a pump, atomized in a nebulizer and broken up and ionized in an argon plasma in a so-called torch. The mostly singly charged ions are focused in a high vacuum with the help of an electric lens, separated in a quadrupole according to their mass / charge ratio and then hit a detector that records the number of ions per mass and thus enables a quantitative analysis of the elements.

The ICP-MS combines the ability of a multi-element analysis as well as the wide linear working range from the ICP-OES with the very good detection limits of the graphite tube AAS and even exceeds them. It is also one of the few analytical techniques that allows the quantification of isotope concentrations when analyzing the elements. However, due to the bottleneck at the transition from argon plasma to high vacuum, only limited salt loads can be introduced. Expensive high-resolution devices (sector field devices with resolutions up to approx. 10,000) can differentiate between atomic and molecular masses in the range of decimal places; they thus separate molecular interferences from the actually measured elemental masses. Their sensitivity is increased again by a factor of 1000 compared to the quadrupole devices. Because of their low substance requirement, they are also ideally suited for the analysis of radioactive samples.

Nuclear magnetic resonance spectroscopy

The method is based on nuclear magnetic resonance , a resonant interaction between the magnetic moment of atomic nuclei in the sample, which is located in a strong static magnetic field , and a high-frequency alternating magnetic field. Only those isotopes are accessible to spectroscopy that have a nuclear spin different from zero in the ground state and thus have a magnetic moment.


  • DA Skoog, JJ Leary: Instrumental Analytics. Springer, Berlin 1996, ISBN 3-540-60450-2 .
  • DC Harris: Quantitative Chemical Analysis. 7th edition, WH Freeman and Company, New York 2003, ISBN 0-7167-7694-4 .
  • K. Cammann: Instrumental Analytical Chemistry. Spektrum Akademischer Verlag, 2000, ISBN 3-8274-0057-0 .
  • G. Wünsch: Optical analytical methods for the determination of inorganic substances. In: Göschen Collection. Vol. 2606, Verlag de Gruyter, Berlin, ISBN 3-11-003908-7 .

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