These are the most accurate and used physical analysis techniques. They use the interaction between electromagnetic radiation and matter. Among these methods, it is little mentioned: spectrophotométries absorption in the visible, ultraviolet and infrared, electron microscopy, the emission spectroscopy, the atomic absorption spectroscopy, and the diffraction X-ray. Visit for more.

The Techniques

Most of these techniques use the same principle. The matter is crossed by electromagnetic radiation and absorbs and emits energy because it undergoes the following phenomena: transition of electrons between the energy levels of the molecule, vibrations or rotations of interatomic bonds, modifications of electronic spins (see Atom  , quantum theory). Thus, the spectrometers emit electromagnetic radiation which passes through the compound under study and records the absorption or emission spectrum, which makes it possible to determine the wavelengths and the intensities of the radiation absorbed or emitted by the material. These wavelengths are characteristic of an (organic) functional group, and the relative intensities of the emission or absorption lines make it possible to determine the proportion of the corresponding constituents in the molecule.

Visible or ultraviolet absorption spectrophotometry is a widely used analytical technique for mineral and organic substances. The spectrophotometer measures the absorbance (related to the amount of light absorbed) of a solution containing the sample, before and after the solution have reacted with a dye reagent. The decrease in the transparency of the solution is proportional to the concentration of the component analyzed.

  • Infrared absorption spectrophotometry is effective for organic analysis because the bonds of different functional groups have very different energies, and therefore absorb infrared radiation at different frequencies. The corresponding absorption spectrum consists of peaks.
  • Fluorescence spectroscopy uses the inverse phenomenon of absorption spectrophotometry. The molecules are excited and emit light at the characteristic energies of their structure, and at intensity proportional to the concentration of the sample. This method gives very precise quantitative results for certain molecules.

In atomic absorption or emission spectrometry, the sample is heated to a high temperature and decomposes into atoms and ions, which emit or absorb radiation in the visible or ultraviolet range, respectively, and at characteristic energies. Elements involved. Atomic absorption spectroscopy is widely used for qualitative and quantitative analyses of trace metal elements.

X-ray fluorescence spectroscopy is used for qualitative and quantitative analyses of metallic elements that emit X-rays at characteristic energies when they are bombarded by a high-energy X-ray source.

Radiochemical methods

These methods consist in detecting the radioactivity of the sample in the form of alpha and beta particles, and gamma rays, produced by nuclear decays. The radioactivity of a sample can be generated by neutron bombardment. This process is commonly used in industry to identify certain metals in a compound. This method of neutron activation analysis has the advantage of being fast, highly automated, and not destroying the sample.

Nuclear Magnetic Resonance (NMR)

The studied molecule is placed in a magnetic field: a nuclear spin transition occurs during the absorption of electromagnetic energy by the molecule. The NMR spectrum of a compound consists of peaks. The position of the peaks and their relative intensity give access to the molecular structure.