Atomic Absorption Spectrometry (1)

1.

1.

In the 18th century, Wu Langston, Furao and Fei observed atomic absorption lines in the solar spectrum

In 1929, the Swedish agronomist Lwndegardh used air-acetylene flame and pneumatic spray spectroscopy to perform flame photometric analysis

Since 1976, advanced technologies such as graphite furnace atomization technology and Zeeman effect background correction have gradually been widely used in clinical testing, environmental protection, biochemistry and other fields

2.

Atomic absorption spectrophotometric analysis is based on the characteristic spectral line of the element to be measured radiated from the light source, and is absorbed by the ground state atom of the element to be measured when passing through the sample vapor, and the content of the element to be measured in the sample is determined by the degree to which the characteristic spectral line is weakened.

The characteristic radiation emitted by the same kind of atomic sharp light source is used to irradiate the atomized flame layer atomic vapor of the sample solution to measure the transmitted light intensity or absorbance, and calculate the content of the measured element in the sample according to the relationship between absorbance and mass concentration

3.

(1) High selectivity and low interference

(2) High sensitivity

(3) Fan Guang of analysis

(4) Simple operation and fast analysis speed

(5) High accuracy

4.

(1) Mainly composed of light source, atomization system, spectroscopic system, and detection system

(2) Flame atomizer structure: It is composed of atomizer, pre-mixing chamber, burner and flame
.
According to the temperature required for the dissociation of the element to be measured into ground state atoms, low temperature flame gas source air-acetylene (temperature 2300K) or high temperature flame source gas acetylene-nitrous oxide (temperature up to 3000K) can be selected
.

(3) graphite furnace atomic structure: by the power supply, a graphite tube furnace, gas protection system, cooling system components
.
Generally, the power supply voltage is low, and the current can reach 500A.
Graphite tubes are required to be made of spectral pure graphite materials
.

5.
Selection of instrument conditions

(1) Selection of analysis line: Choose the resonance line with the highest sensitivity as the analysis line.
When measuring high-content elements or the resonance line has interference, select other spectral lines
.

(2) Selection of the spectral passband: the width of the wavelength range of the beam emitted by the monochromator, and the maximum slit width that does not cause a decrease in absorbance is an appropriate slit width
.

(3) Selection of lamp current: Under the condition of ensuring sufficient intensity and stable spectral output, try to choose a low lamp current, generally about 50% of the rated current
.

(4) Selection of atomization: flame atomization (select flame type, fuel-assistance ratio, burner height, etc.
), adjust the burner height so that the characteristic spectrum of the element to be measured passes through the area with the largest ground state atom density to improve analysis sensitivity
.

6.
Types of atomic absorption spectrophotometer

(1) Single beam atomic absorption spectrophotometer
.
It is characterized by simple structure and low price; however, it is easily affected by changes in the intensity of the light source, the lamp has a long warm-up time, and the analysis speed is slow
.

(2) Double beam atomic spectrophotometer
.
A beam of light passes through the flame, and a beam of light does not pass through the flame, but passes directly through the monochromator
.
This type of instrument can eliminate the influence of light source intensity changes, the influence of detector sensitivity changes, and the interference of certain impurities
.

7.
Matters needing attention in standard accession method

(1) The mass concentration of the element to be tested has a linear relationship with the corresponding absorbance
.

(2) In order to obtain accurate analysis results, at least 4 points should be used as the extrapolation curve
.

(3) This method can eliminate the influence caused by the matrix effect, but it cannot eliminate the background absorption
.

(4) The mass concentration of the added standard solution should be appropriate, and the slope of the curve is too large or too small will cause large errors
.

8.
Interference and suppression of atomic absorption

The interference of atomic absorption is mainly manifested in five aspects: physical interference, chemical interference, spectral interference, background interference and ionization interference (Table 5-1)
.

Table 5-1 Generation and elimination of interference from atomic absorption