What Is an Atomic Absorption Spectrophotometer?

Atomic absorption spectrometer, also known as atomic absorption spectrophotometer, performs metal element analysis based on the role of atomic vapors in the ground state of materials on the absorption of characteristic radiation. It can sensitively and reliably determine trace or trace elements.

In 1802 WHWollaston discovered many dark lines in the continuous spectrum of the sun.

In 1814, J. Fraunhofer observed these dark lines again, but could not explain them. These dark lines were called the Frauhofer dark lines.

In 1820 D. Brewster first explained that these dark lines were generated by the absorption of sunlight by the outer atmosphere of the sun.

In 1860, G. Kirchoff and R. Bunsen proved that the D line of the dark line in the continuous spectrum of the sun was based on the fact that the positions of the sodium (Na) emission line and the Frauhofer line were the same. Is the result of the absorption of Na spectrum in the solar spectrum by Na atoms in the outer atmosphere of the sun; and further clarifies the relationship between absorption and emission-gaseous atoms can emit certain characteristic spectral lines, and can also absorb these spectral lines of the same wavelength . This is the first example of qualitative analysis in history using atomic absorption spectroscopy.

For a long time, atomic absorption was mainly confined to the research of astrophysics, and its application in analytical chemistry has not attracted much attention. The main reason is that no light source capable of generating sharp-line spectra has been found.

In 1916, Paschen first developed a hollow cathode lamp, which can be used as a light source for atomic absorption analysis.

Until the 1930s, due to the widespread application of mercury, the determination of trace mercury in the atmosphere was designed using the principle of atomic absorption spectroscopy, which was the earliest application of atomic absorption in analysis.

In 1954, the Institute of Physics, Melbourne, Australia exhibited the world's first atomic absorption spectrophotometer at the exhibition. The use of hollow cathode lamps has led to the development of commercial instruments for atomic absorption spectrophotometers.

In 1955, A. Walsh, a physicist at the Commonwealth Institute of Science and Industry in Australia, first proposed atomic absorption spectroscopy as a general analysis method to analyze the possibility of each element, and explored the relationship between atomic concentration and absorbance value. And related problems in the experiment. Then he published the famous paper "Application of Atomic Absorption Spectroscopy in Analysis" in the Chinese Journal of Spectroscopy. Since then, scientists from some countries have competed to carry out research in this area and have made great progress. With the development of science and technology, cutting-edge sciences such as atomic energy, semiconductors, radio electronics, and space navigation have increasingly demanded material purity, such as uranium, thorium, beryllium, zirconium, and other atomic energy materials. ⁸ g, impurities in semiconductor materials germanium and selenium must be less than 10 ^-10 ~ 10 ^-11 g, and impurities in thermonuclear reaction structural materials must be less than 10 ^-12 g. Atomic absorption analysis can better meet the requirements of ultra-pure analysis.

Before 1959, Soviet scholar Lviv (.B.BOB) designed a graphite furnace atomizer. In 1960, an electrothermal atomization method (ie, non-flame atomic absorption method) was proposed, which greatly improved the sensitivity of atomic absorption analysis. improve.

In 1965, Venice (JB Willis) used a nitrous oxide-acetylene flame in the atomic absorption method to increase the number of measurable elements to 70.

In 1967, H. Massmann improved the Lviv graphite furnace and designed an atomizer for high-temperature graphite furnace (ie, high-temperature graphite furnace).

The "indirect atomic absorption spectrophotometry" was developed in the late 1960s, making it possible to determine elements and organic compounds that were difficult to measure by direct methods in the past.

In 1971, the American Varian company produced the world's first longitudinally heated graphite furnace, and first developed the Zeemen background correction technology.

In 1981, the atomic absorption analyzer was automated.

The first continuous hydride generator was introduced in 1984.

In 1990, the world's most advanced Mark V1 flame burner was launched.

In 1995, the online flame autosampler (SIPS8) was successfully developed and put into use.

In 1998, the first rapid analysis flame atomic absorption 220FS was born.

In 2002, the world's first atomic absorption spectrometer for simultaneous analysis of flame and graphite furnace was produced and put on the market.

At present, the atomic absorption spectrophotometer uses the latest electronic technology to digitize the display of the instrument and automate the sampling. The computer data processing system automates the entire analysis.

China began to introduce atomic absorption spectrophotometry in 1963. In 1965, Fudan University's electric light source laboratory and the non-ferrous metal research institute of the Ministry of Metallurgical Industry successfully developed hollow cathode lamp light sources. In 1970, Beijing Science Instrument Factory made a WFD-Y1 single-beam flame atomic absorption spectrophotometer. At present, many enterprises in China have produced various types of atomic absorption spectrophotometers with advanced performance.

The application of atomic absorption spectrophotometry also has certain limitations, that is, each element to be measured must have a light source that can emit a specific wavelength line. In atomic absorption analysis, the element to be measured must first be in an atomic state, and atomization is often achieved by spraying a solution into a flame. This has physical and chemical interferences, making the determination of poorly soluble elements not ideal, There are only more than 30 elements with ideal results. As the instrument is used, acetylene, hydrogen, argon, nitrous oxide (commonly known as laughing gas), etc. must be used, and safety must be observed during operation. ^[1]

Atomic absorption spectrophotometer generally consists of four parts, namely the light source (monochromatic sharp line radiation source), sample atomizer, monochromator and

Elements are heated and atomized in a pyrolytic graphite furnace to become ground-state atomic vapors, which selectively absorb characteristic radiation emitted by hollow cathode lamps. Within a certain concentration range, its absorption intensity is directly proportional to the content of the test element in the test solution. The quantitative relationship can be based on Lambert-Beer law, A = -lg I / I o = -lgT = KCL, where I is the intensity of transmitted light; I0 is the intensity of emitted light; T is the transmittance; L is the light through atom Device optical path (length), the L value of each instrument is fixed; C is the concentration of the measured sample; so A = KC.

The device that uses the resonance radiation of the element to be measured to measure its absorbance through its atomic vapor is called an atomic absorption spectrophotometer. It has single beam, dual beam, dual channel, multi-channel and other structural forms. Its basic structure includes a light source, an atomizer,

The advantages of the flame atomization method are: the flame atomization method is easy to operate, has good reproducibility, a large effective optical path, and has high sensitivity to most elements, so it is widely used. Disadvantages are: low atomization efficiency, insufficient sensitivity, and generally cannot directly analyze solid samples;

The advantages of the graphite furnace atomizer are: high atomization efficiency, 100% sample utilization at adjustable high temperature, high sensitivity, small sample usage, suitable for determination of refractory elements. Disadvantages are: the influence of sample composition heterogeneity is large, the measurement precision is low, the interference of coexisting compounds is greater than the flame atomization method, the interference background is more serious, and the background needs to be corrected generally. ^[2]

Atomic absorption spectrometry is now widely used in various analytical fields, mainly in four aspects: theoretical research; elemental analysis; organic matter analysis; metal chemical speciation analysis.
1. Applications in theoretical research:
Atomic absorption can be used as an experimental method in physics and physical chemistry to measure and study some basic properties of substances. The electrothermal atomizer is easy to control the evaporation process and atomization process, so using it to determine some basic parameters has many advantages. The activation energy, gaseous atomic diffusion coefficient, dissociation energy, oscillator strength, broadening of the spectral line profile, solubility, vapor pressure, etc. of some elements leaving the body measured by the electrothermal atomizer.
2. Application in element analysis:
Atomic absorption spectroscopic analysis, due to its high sensitivity, low interference, and simple and fast analysis methods, is currently widely used in various fields such as industry, agriculture, biochemistry, geology, metallurgy, food, environmental protection and so on. One of the powerful tools and is used as a standard analysis method in many areas. The characteristics of atomic absorption spectrometry determine its important position in geological and metallurgical analysis. It not only replaces many general wet chemical analysis, but also has the same status as X-ray fluorescence analysis and even neutron activation analysis. .

At present, the atomic absorption method is used to determine more than 70 elements in geological samples, and most of them can achieve sufficient sensitivity and good precision. The analysis of various trace elements in steel, alloys and high-purity metals is now more commonly performed by atomic absorption. Atomic absorption is becoming more widespread in food analysis. More than 20 elements in food and beverages have satisfactory atomic absorption analysis methods. The analysis of essential and harmful elements in biochemical and clinical samples now uses atomic absorption. The literature on atomic absorption analysis of metal elements in petroleum products, ceramics, agricultural samples, pharmaceuticals and coatings has been increasing in recent years. Analysis of trace metal elements in environmental samples such as water bodies and the atmosphere has become one of the important fields of atomic absorption analysis. Indirect atomic absorption method can also determine some non-metal elements.
3 Applications in organic analysis:
Indirect methods can be used to determine a variety of organics. 8- hydroxyquinoline (Cu), alcohols (Cr), aldehydes (Ag), esters (Fe), phenols (Fe), biacetyl (Ni), phthalic acid (Cu), fatty amines (co) , Amino acid (Cu), vitamin C (Ni), anthranilic acid (Co), remifen (Cu), quinine formate (Zn), organic acid anhydride (Fe), benzyl penicillin (Cu), glucose (Ca ), Epoxide hydrolase (PbO, halogen-containing organic compound (Ag), and other organic substances are all indirectly determined by the stoichiometric reaction with the corresponding metal element.
4 Applications in metal chemical speciation analysis:

By gas chromatography and liquid chromatography separation and then determination by atomic absorption spectrometry, different organic compounds of the same metal element can be analyzed. For example, 5 kinds of alkyl lead in gasoline, 5 kinds of alkyl lead in the atmosphere, alkyl selenium, alkyl rhenium, alkyl tin, alkyl rhenium in water, alkyl lead, alkyl ether, alkyl mercury, organic Chromium, a variety of metal organic compounds such as alkyl lead, alkyl mercury, organic zinc, organic copper, etc. can be identified and measured by different types of spectral atomic absorption. ^[2]

First, the total power indicator is off

cause of issue

1. Instrument power cord is open circuit or poor contact 2. Instrument fuse is blown 3. Poor contact of fuse

elimination method

1. Connect the power cord, press the plug 2. Replace the fuse 3. Clamp the fuse to make good contact

2. "X" appears in the middle wavelength motor during initialization

cause of issue

1. Whether the hollow cathode lamp is installed 2. Objects are blocked in the light path 3. Communication system connection is interrupted

elimination method

1. Reinstall the lamp 2. Remove the obstruction in the light path 3. Restart the instrument

Third, the element light does not light

cause of issue

1. Whether the power cord is de-soldered 2. Whether the lamp power socket is loose 3. The lamp is broken

elimination method

1. Reinstall the lamp 2. Replace the lamp position 3. Change the lamp

Fourth, the energy is too low during peak seeking, the energy exceeds the upper limit

cause of issue

1. Element light does not light up 2. Element light position is wrong 3. Lamp aging

elimination method

1. Reinstall hollow cathode lamp 2. Reset lamp position 3. Replace with new lamp

Fifth, click "Ignition", no high-voltage discharge sparks

cause of issue

1. No pressure in the air 2. The acetylene is not turned on 3. The waste liquid level is low 4. The acetylene leaks and alarms

elimination method

1. Check the air compressor 2. Check the acetylene outlet pressure 3. Add distilled water 4. Turn off the emergency fire

Six, the test baseline is unstable and noisy

cause of issue

1. Low energy of the instrument, high negative pressure of the multiplier tube 2. Inaccurate wavelength 3. Unstable emission of elemental lamps

elimination method

1. Check the lamp current 2. Whether peak finding is normal 3. Replace the known lamp

Seven, the standard curve is bent

cause of issue

1. The light source lamp is out of gas 2. The working current is too large 3. The waste liquid does not flow smoothly 4. The sample concentration is high

elimination method

1. Replace lamp or reverse connection 2. Reduce current 3. Take measures 4. Reduce sample concentration

Eight, the analysis results are high

cause of issue

1.Solid solids are not dissolved 2.Background absorption artifact 3.Blank uncorrected 4.Deterioration of standard solution

elimination method

1. Increase the flame temperature 2. Retest near the resonance line 3. Use a blank 4. Remake the standard solution

Nine, the analysis results are low

cause of issue

1. The sample is not completely volatilized 2. The standard solution is not prepared properly 3. The sample concentration is too high 4. The sample is contaminated

elimination method

1. Adjust the relative position of the impact ball and the nozzle 2. Reconfigure the standard solution 3. Reduce the sample concentration 4. Eliminate pollution ^{[2] [4]}