原子吸收分光光度计（Atomic absorption spectrophotometer）

1、原子吸收分光光度计（Atomic absorption spectrophotometer）Atomic absorption spectrophotometer: the basic principle of the instrument from the light source radiation with the measured spectral line of light, when the steam by the steam through the specimen to be measured in the ground state of the atom elements

2、absorbed by the radiation characteristic spectrum of light is reduced the degree of determination of sample analyte.Two. The use of atomic absorption spectrophotometer:Atomic absorption spectrophotometer can be used to determine a variety of elements, flame atomic absorption spectrometry can be meas

3、ured 10-9g/mL orders of magnitude, graphite furnace atomic absorption spectrometry can be measured 10-13g/mL order of magnitude. The hydride generator can be used for the determination of 8 kinds of volatile elements such as mercury, arsenic, lead, selenium, tin, tellurium, antimony, germanium and s

4、o on.Atomic absorption spectrometryeditAtomic absorption spectrometry (Atomic Absorption Spectroscopy, AAS), namely, atomic absorption spectrometry, gaseous atomic electrons on the range of ultraviolet and visible light corresponding to the strength analysis method to quantitatively measured element

5、 content based atomic absorption resonance radiation is based on a method of measuring specific absorption of gaseous atoms optical radiation. This is the last century in the middle of 50s and a new instrument gradually developed analysis method, it has been widely used in various fields of geology,

6、 metallurgy, machinery, chemical industry, agriculture, food, light industry, biological medicine, environmental protection, material science etc. This method is mainly suitable for the analysis of trace and trace components in samples.Catalog1 brief introduction2 basic principles3 line profile4 ins

7、trument structure5 interference effect6 main features6.1 superiority6.2 limitations7 history of development8 research prospects1 brief introductionAtomic absorption spectrometry (AAS) is the use of gaseous atoms to absorb a certain wavelength of light radiation, so that the outer layer of the electr

8、on from the ground state transition to the excited state of the phenomenon of the establishment of. Because the energy of the electronic atoms in different, there will be selective radiation to certain resonance absorption wavelength, the resonance absorption wavelength is equal to the atomic emissi

9、on spectrum of the excitation wavelength, which can be used as the basis of qualitative elements, and the absorption intensity of the radiation can be used as a quantitative basis. AAS has become one of the most widely used analytical methods for quantitative analysis of inorganic elements.With a lo

10、w detection limit of atomic absorption spectrometry method (the method can reach g/cm flame - 3 grade) with high accuracy (flame relative error less than 1%), good selectivity (i.e. less interference) analytical speed, wide range of application (flame method can analyze 30 kinds of /70 elements, gra

11、phite furnace method can analyze 70 kinds of analysis of elements, 11 elements of hydride generation) 1 etc.Absorption path in the temperature conditions, fixed sampling experiments, the samples generated by the measured elements of the atomic radiation by hollow cathode lamp as the light source of

12、the sharp line elements produce monochromatic light absorption, the absorbance (A) and the concentration of the element in the sample (C) than Cheng Zheng. In A=KC form, K is constant. Accordingly, the standard curve can be used as the standard curve by measuring the absorbance of standard solution

13、and unknown solution, and the concentration of standard solution can be obtained, and the concentration of the elements to be measured in unknown liquid is obtained.This method is mainly suitable for the analysis of trace and trace components in samples.2 basic principlesThe atoms of each element ca

14、n emit not only a series of characteristic lines, but also the absorption and emission of line wavesPrinciple diagram of atomic absorption spectrometryPrinciple diagram of atomic absorption spectrometryCharacteristic lines of the same feature. When a characteristic wavelength of light emitted light

15、by atomic vapor, which is equal to the frequency of the incident radiation of electrons in an atom from the ground state to a higher energy state (generally the first excited state energy) frequency required, characteristics of the outer electrons in the atoms of the same element will selectively ab

16、sorb the emission the spectrum of the incident light. The degree of attenuation of characteristic spectral lines due to absorption is called absorbance A, which is directly proportional to the content of the elements being measured:A=KCK is constant in the formula; C is the concentration of the samp

17、le; K contains all constants. This formula is the theoretical basis for quantitative analysis by atomic absorption spectrometryBecause the atomic energy level is quantized, therefore, in all cases,The absorption of atoms by radiation is selective. Because the atomic structure of each element and the

18、 arrangement of outer electrons are different, the energy absorbed by the element from the ground state transition to the first excited state is different, so the resonant absorption lines of each element have different characteristics. The atomic absorption spectrum is located in the ultraviolet an

19、d visible regions of the spectrum.3 line profileAtomic absorption lines are not strictly geometric lines, but rather finite, narrow frequency bandsAtomic absorption spectrometry curveAtomic absorption spectrometry curveOr wavelength range, that is, a certain width. The atomic absorption spectrum is

20、characterized by the central wavelength and half width of the atomic absorption spectrum. The central wavelength is determined by atomic energy levels. Half width refers to the difference of the frequency difference or the wavelength difference between the two points of the absorption line contour a

21、t the center wavelength. Half width is influenced by many experimental factors. Two main factors affecting the atomic absorption spectrum line profile:1. Doppler broadening. The Doppler width is due to the thermal motion of atoms. Known from the physics, from a moving atoms emit light, if the motion

22、 in the direction away from the observer, the observer opinion, issued by the frequency is a static atom light frequency is low; on the contrary, such as atomic movement toward an observer, the frequency of a stationary atoms emit light frequency is high, this is Doppler effect. The analysis for ato

23、mic absorption, flame and graphite furnace atomic absorption pool, gaseous atoms in disordered thermal motion, relative to the detector, the light has a different atomic motion component, even if each atom emits light is monochromatic light with the same frequency, but the detector receiving light f

24、requency is slightly different light. So the spectral line broadening of the.2. Collision broadening. When the atomic concentration in the atomic absorption region is high enough, the collision broadening is not negligible. Because the atom is stable, its life can be regarded as infinite, so the ato

25、mic absorption spectrometry used by the resonance absorption line, line width is only related to the average lifetime of the excited atoms, the average life expectancy is longer, narrower line width. Collisions between atoms cause the average lifetime of the excited atoms to shorten and cause the br

26、oadening of the spectral lines. Collision broadening is divided into two kinds, namely Mark hruz is wider and wider lorenz.Hruz Mark broadening refers to excited atoms and ground atoms collide with each other due to a broadening of the measured elements, called resonance broadening, also known as Ma

27、rk hruz wide or wider pressure. In the usual atomic absorption determination conditions, atomic vapor pressure measured elements are rarely more than 10-3mmHg, the resonance broadening effect can not be considered when the vapor pressure reaches 0.1mmHg, the resonance broadening effect is obvious. L

28、orenz width refers to the measured element atoms and other elemental atoms collide with each other due to the wide, wide known as lorenz. Lorenz becomes wider with increasing atomic vapor pressure in the region increases with temperature increasing.In addition to the above factors, there are other f

29、actors that influence the broadening of spectral lines, such as field broadening and self absorption effects. But the absorption analysis experimental conditions in the usual atomic absorption line profile, influence mainly by Doppler and Lorenz widened. In the temperature range of 2000-3000K, the w

30、idth of the atomic absorption line is about 10-3-10-2nm.4 instrument structureAtomic absorption spectrometer consists of light source, atomization device, spectrophotometer, detection system and other parts. The basic structure is on the rightStructure diagram of atomic absorption spectrometerStruct

31、ure diagram of atomic absorption spectrometer1. Light source. The function of the light source is to emit characteristic resonant radiation of the element to be measured. The basic requirements of the light source is the half width of the resonance radiation emission was significantly less than the

32、half width of the absorption line; radiation intensity, low background, characteristic of the resonance radiation intensity lower than 1%; the stability is good, within 30 minutes of drift is less than 1%; the noise is less than 0.1%; long service life to 5 ampere hours. Hollow cathode discharge lam

33、p is an ideal sharp line light source which can meet the above requirements and is widely used.2. Atomization. Its function is to provide energy, so that the sample drying, evaporation and atomization.In atomic absorption spectrometry analysis, the atomization of the elements in the sample is the ke

34、y link in the whole analysis process. There are two kinds of methods to realize atomization:Flame atomization is the earliest atomization method used in atomic spectrum analysis, and is still widely used today;Non flame atomization method, the most widely used method is graphite furnace electrotherm

35、al atomization.3. Splitter. It consists of incident and exit slits, mirrors and dispersive elements. The effect is to separate the required resonant absorption lines. The key component of the optical splitter is the dispersion element, and the commercial instruments use the grating. The resolution o

36、f the atomic absorption spectrometer is not high enough. It can be used to distinguish the open nickel three line Ni230.003, Ni231.603, Ni231.096nm as the standard, and then use Mn279.5 and 279.8nm instead of Ni three line to verify the resolution. The grating is placed behind the atomization device

37、 to prevent all unnecessary radiation from the detector into the detector.4, detection system. The detector widely used in atomic absorption spectrometer is photomultiplier tube, and some instruments also use CCD as detector.5 interference effectAtomic absorption spectrometry and atomic emission spe

38、ctrometry in analysis, although less interference and easy to overcome, but in the actual work interference effect still occurs frequently, and sometimes very serious, so understanding type essence interference effect and its inhibition method is very important. The interference effects in atomic ab

39、sorption spectrometry can be divided into four types: physical interference, chemical interference, ionization interference and spectral interference.1 、 physical interference and its suppressionPhysical interference is due to differences in physical properties of solution and standard solution, the

40、 interference caused by the injection speed, injection volume, atomizing efficiency and atomization efficiency due to the change of. Remove and inhibit the physical interference often adopts the following methods:(1) prepare the standard solution which is similar to the sample solution to be tested,

41、 and determine it under the same conditions. If the sample composition is unknown, using the standard addition method can eliminate physical interference.(2) as far as possible to avoid using the viscosity of the sulfuric acid and phosphoric acid treated samples; when the solution concentration is h

42、igh, the appropriate dilution solution can also inhibit the physical interference.2. Chemical interference and its inhibitionChemical interference is due to the measured elements and coexisting components undergo chemical reactions, volatile compounds generated from difficult or obscure, to reduce t

43、he number of ground atoms generated by interference. Chemical interference is the main interference in atomic absorption spectrometry. This interference is selective and has different effects on various elements in the sample. There are many factors affecting the chemical interference, but they are

44、mainly determined by the properties of the determined elements and coexisting elements. In addition, it is also related to the type of flame and the nature of flame.In the process of flame and graphite furnace atomization, the mechanism of chemical interference is very complex. To eliminate or restr

45、ain its chemical interference, the following specific measures should be taken according to the specific situation:(1) increasing the flame temperature and properly increasing the flame temperature make it difficult to volatilize and make the compound more complete ground state atomization.(2) addin

46、g diluents, adding release agents and interfering elements to produce more stable or more volatile compounds, so that the determined elements are released from compounds containing interfering elements.(3) most of the protective agents are organic complexes. It forms a stable complex with the determ

47、ined elements or interfering elements to avoid the generation of volatile compounds from the determined elements and interfering elements.(4) adding modifier with graphite furnace atomic absorption spectrometry, adding some chemical reagents to test or change the thermal stability of graphite tube i

48、n the body or the element compound is measured, to avoid chemical interference, these chemicals known as matrix modifier.(5) the chemical separation method separates the elements to be interfered with the interfering elements by chemical method. It can not only eliminate the interference of the matr

49、ix elements, but also enrich the elements to be determined.3. Ionization interference and its suppressionIonization of some ionizable elements in the flame reduces the number of ground state atoms and reduces the sensitivity of the element determination. This interference is called ionization interf

50、erence.Elements and compounds with low temperature flame or adding an excess of more easily ionized in solution (the deionization agent), can effectively suppress the ionization of the measured elements. Commonly used ionization inhibitors are CsCl, KCl, NaCl and so on.4 、 spectral interference and

51、its suppressionThere are two kinds of spectral interferences in atomic absorption spectrometry: spectral line interference and background interference.(1) spectral line interference and its suppressionSpectrum interference refers to the monochromator spectrum band in addition to the absorption line,

52、 also entered the adjacent line emission lines or other absorption lines, the analysis method of the sensitivity and accuracy of the decline. The adjacent line interference emission line is mainly refers to the overlapping interference emission lines of the hollow cathode lamp elements, impurity or

53、gas elements and the measured elements resonance absorption lines; other absorption line interference mainly refers to the coexistence of elements in the sample to be measured elements of absorption lines and resonance line overlap interference.Inhibition of spectral interferences is usually reduced

54、 spectral passband width of the monochromator slit width decreases, improve the resolution of the instrument, the elements of the resonance absorption line and the interference curve completely separated. According to the specific circumstances can also inhibit the spectral interference by using the

55、 following methods, such as reducing the lamp current, select other absorption lines without interference, hollow cathode lamp with high purity single element, separation of coexisting interfering elements method.(2) background interference and suppression1. background interference and background in

56、terference in the suppression of atomic absorption spectrometry mainly refer to the interference produced by the molecular absorption during the atomization process and the light scattering produced by solid particles. Background interference often increases the absorbance and produces positive erro

57、rs.Suppression and correction of 2. spectral background interferenceInhibition of A. background interference in the practical work, the change of flame type, fuel ratio and can adjust the flame height observation area to suppress the molecule absorption; in the graphite furnace atomic absorption spe

58、ctroscopy, and often choose the appropriate matrix modifier to suppress interference molecular absorption using selective volatilization.Background correction of B. spectrum is in atomic spectrum analysis. The methods of correcting background include instrumental zero absorption method, near line correction background method, deuterium lamp correction background method and Zeeman effect correction background method.6 main featuresSuperiority1 strong selectivity. This is because the atomic absorption bandwidth is very narrow. Therefore, the determination is fast and simple, and the conditio