The hollow cathode lamp has played an important role in promoting the establishment of atomic absorption spectrometry.

Atomic absorption spectrometry (AAS) is a quantitative analysis method based on the properties of the ground state atoms dispersed into vapor state, which absorb the characteristic light radiated by the same kind of atoms.

The atoms of each element can not only emit a series of characteristic lines, but also absorb the same characteristic lines as the wavelength of the emission lines. When light of a certain characteristic wavelength emitted by a light source passes through the atomic vapor, the outer electrons in the atom will selectively absorb the characteristic spectral lines emitted by the same element, thus weakening the incident light.

In the early 1950s, the development of high quality closed hollow cathode lamp has greatly promoted the establishment of atomic absorption spectrometry. Until now, hollow cathode lamp is still the most widely used light source. This is a special gas discharge tube using abnormal glow discharge. It is usually made of suction metal titanium and tantalum as anodes. The hollow cylindrical cathode is made of metal materials containing elements to be measured. The modulated voltage is applied between the two electrodes to keep the glow discharge in the cathode cavity. The atoms sputtered from the cathode material and other particles are charged. The incoming inert gas atoms or ions collide with stimulated luminescence. Such conditions can radiate strong enough, pure, sharp and stable characteristic lines. Although microwave-excited electrodeless discharge lamps have been developed in recent years, they are limited to a few elements with high vapor pressure of halides.

In order to convert the analytical sample into the corresponding atomic vapor, a special atomization device must be provided for the accessories of atomic absorption spectrometer. At present, there are two ways of flame atomization and electrothermal atomization. The former sprays the sample solution with the carrier gas into a high temperature chemical flame burner and atomizes the sample at the high temperature of the flame; the latter uses an electric heating furnace, tube, wire or flake atomizer made of different materials (such as graphite, tungsten, tantalum, quartz, etc.) to heat the sample in the atomizer for evaporation and atomization. Flame atomization has the advantages of simple operation, rapid operation and wide application range. The disadvantage is that the sample is diluted by carrier gas and gas, so the efficiency is low, the flame chemical interference and the sample consumption is large. In 1959, Soviet physicist Livov first applied the principle of graphite furnace evaporation in atomic emission spectrometry (AES) to atomic absorption spectrometry (AAS), and initiated non-flame atomization. In the following decade, various types of electrothermal atomization devices emerged, of which graphite furnace was one of the earliest developed. It has the advantages of high absolute sensitivity (10-10 g), small sample size (micro-upgrade) and direct determination of solid and liquid. The disadvantage is low speed and high cost.

application

Atomic absorption spectrometry (AAS) is based on the absorption of the characteristic radiation of the light source by the ground state atoms which exist stably under the experimental conditions, and the influence of the external conditions on it is small. Compared with atomic emission spectrometry, this method has higher accuracy, better selectivity and higher sensitivity to some elements.

Atomic absorption spectrometer accessories