Introduction to atomic absorption spectrometry

　　1. Graphite furnace atomic absorption spectrometry can be used to determine the content of metal elements in water, biological samples, plants and food, non-ferrous metals and alloys, coal, petrochemicals, environmental substances, geological minerals, glass and semiconductor materials.

　　2. Flame furnace atomic absorption spectrometry can be used to determine the content of metal elements in natural water, wastewater, seawater, biological samples, food, traditional Chinese medicine, non-ferrous metals and alloys, industrial raw materials and chemical products, and geological samples.

　　Basic principle:

　　The scientific instrument radiates light with characteristic spectral lines of the element to be measured from the light source. When the light passes through the sample vapor, it is absorbed by the ground state atoms of the element to be measured in the vapor. The content of the element to be measured in the sample is determined by the degree to which the characteristic spectral line light is weakened.

　　use:

　　The atomic absorption spectrometer can measure a variety of elements. The flame atomic absorption spectrometry can measure up to 10-9g/ml, and the graphite furnace atomic absorption method can measure up to 10-13g/ml. Its hydride generator can measure trace amounts of eight volatile elements, including mercury, arsenic, lead, selenium, tin, tellurium, antimony, and germanium.

Due to the sensitivity, accuracy and simplicity of 　　atomic absorption spectrometers , they are now widely used in the analysis of major and trace elements in metallurgy, geology, mining, petroleum, light industry, agriculture, medicine, health, food and environmental monitoring .

　　Basic knowledge:

　　1. Principle of the method

　　Atomic absorption refers to the absorption phenomenon of gaseous atoms of characteristic spectral lines radiated by atoms of the same type.

　　Under the stimulation of external radiation light energy of a certain frequency, the outer electrons of the atom transition from a lower energy state to a higher energy state. The spectrum produced by this process is the atomic absorption spectrum.

　　2. Composition of atomic absorption spectrometer

　　The atomic absorption spectrometer is composed of a light source, an atomization system, a spectroscopic system and a detection system.

　　A. Light source

　　As a light source, it is required that the sharp line spectrum of the element to be measured should be of sufficient intensity, small background, and stable.

　　Generally used: hollow cathode lamp electrodeless discharge lamp

　　B. Atomizer

　　It can be divided into premixed flame atomizer, graphite furnace atomizer, quartz furnace atomizer and cathode sputtering atomizer.

　　(a) Flame atomizer: It consists of three parts: atomizer, premixing chamber and burner.

　　Features: easy operation, good reproducibility

　　(b) Graphite furnace atomizer: A system that places the sample on the wall of a graphite tube, a graphite platform, a small hole in a carbon rod or a graphite crucible and electrically heats it to a high temperature to achieve atomization. The tubular graphite furnace is the most commonly used atomizer.

　　The atomization process is divided into drying, ashing, atomization, and high temperature purification.

　　High atomization efficiency: 100% sample utilization at adjustable high temperature

　　High sensitivity: its detection limit is 10-6~10-14

　　Small sample amount: suitable for the determination of refractory elements

　　(c) The quartz furnace atomization system is a method of introducing gaseous analytes into a quartz furnace to achieve atomization at a relatively low temperature, also known as low-temperature atomization. It is mainly used in conjunction with vapor generation methods (hydride generation, mercury vapor generation, and volatile compound generation).

　　(d) Cathode sputtering atomizer uses positive ions generated by glow discharge to bombard the cathode surface, converting the element to be measured directly from the solid surface into atomic vapor.

　　C. Spectroscopic system (monochromator)

　　Consists of concave mirrors, slits or dispersive elements

　　The dispersion element is a prism or a diffraction grating

　　The performance of a monochromator refers to its dispersion, resolution and light-gathering power.

　　D. Detection system rate

　　Consists of a detector (photomultiplier tube), amplifier, logarithmic converter and computer

　　3. Selection of optimal conditions

　　A. Selection of absorption wavelength

　　B. Selection of atomization working conditions

　　(a) Selection of hollow cathode lamp working conditions (including preheating time and working current)

　　(b) Selection of flame burner operating conditions (test liquid lift, flame type, burner height)

　　(c) Selection of optimal operating conditions for graphite furnace (optimal atomization temperature of inert gas)

　　C. Selection of spectral passband

　　D. Selection of detector photomultiplier tube working conditions

　　4. Interference and elimination methods

　　Interference is divided into: chemical interference, physical interference, ionization interference, spectral interference, background interference

　　Chemical interference elimination methods: change the flame temperature, add release agent, add protective complexing agent, add buffer

c Methods to eliminate background interference: dual wavelength method, deuterium lamp correction method, self-absorption method, Zeeman effect method