紫外光譜分析-演講

1、Ultraviolet/Visible spectroscopy Fifth group speaker:Gao xianzheUV radiationUV radiation is the electromagnetic radiation of a wavelength shorter than that of visible light, but longer than that of x-rays. The typical range of UV wavelength is 10-400 nm.UV absorption日常生活中, 各種溶液之所以呈現(xiàn)不同的顏色, 與它對光的選擇性吸收

2、有關。當一束由各種波長按一定比例組成的光透過一溶液時, 某些波長的光被溶液吸收, 而另一些波長的光不被吸收而透過溶液。當透過的光包含有可見光波長范圍內(nèi)的光時, 就可以被人眼察到, 溶液的顏色正是由透過光的波長所決定。 UV/Vis spectroscopyDefinition:Its the analysis methods with analysis,determination and inference of material composition,content and structure by using he uv-vis spectra and the degree of abs

3、orption which produced by material molecules, or ions on the absorption of ultraviolet and visible light. Features: high sensitivity, high accuracy, good selectivity, easy to operate, fast analysis speed, wide application range. COHnp ps sH能量* n* * n*分子中電子的能級和躍遷 2. nss* transition 實現(xiàn)這類躍遷所需要的能量實現(xiàn)這類躍遷

4、所需要的能量較高，較高， 吸收波長為吸收波長為150250nm，大部分在遠紫外區(qū)，大部分在遠紫外區(qū)，近紫外區(qū)仍不易觀察到。近紫外區(qū)仍不易觀察到。 含非鍵電子的飽和烴衍生物含非鍵電子的飽和烴衍生物(含含N、O、S和鹵素等雜原子和鹵素等雜原子)均均呈現(xiàn)呈現(xiàn)n* 躍遷。如躍遷。如CH3OH4. npp* transition 這類躍遷發(fā)生在近紫外光區(qū)這類躍遷發(fā)生在近紫外光區(qū), 一般一般200 nm 。它是簡單的生色。它是簡單的生色團如團如羰基羰基、硝基等中的孤對電子、硝基等中的孤對電子向反鍵軌道躍遷。其特點是向反鍵軌道躍遷。其特點是譜帶譜帶強度弱強度弱，摩爾吸光系數(shù)，摩爾吸光系數(shù)小小，通常，通常小于

5、小于100，屬于禁阻躍遷。，屬于禁阻躍遷。-OH AACCCCCCCCCH3CH3 超共軛效應比共軛效應的影響小的多超共軛效應比共軛效應的影響小的多CCHHCCHH反式反式 大共軛體系大共軛體系 順式順式* n* * n*分子中電子的能級和躍遷 Absorption curve Using different wavelengths of light through a constant concentration and thickness of the solution under test to measure the absorption degree of the solution

6、under test on each wavelength light (absorbance), and then make the wavelength as the abscissa and the absorbance as the ordinate to map a curve. The material absorption capacity of different wavelength can be described by the curve , called absorption curve or absorption spectra. UV-Vis Spectromete

7、rGeneral componentsRadiation sourceMonochromatorSample containerDetectorreadout device 1. 1. Radiation source In the UV region or the visible region of the spectrum can emit continuous spectrum(200-1000 nm), with enough radiation intensity, good stability, long service life. There are two kinds of l

8、ight source, thermal radiation light source and gas discharge light source.Visible light RegionVisible light Region：as a light as a light source, its radiation wavelength range from 320 to source, its radiation wavelength range from 320 to 2500 nm.2500 nm.Ultraviolet light RegionUltraviolet light Re

9、gion： emit Continuous spectrum of 185 to 400 nm.Continuous spectrum of 185 to 400 nm.() monochromatorvMonochromator is the device required monochromatic light from the continuous spectrum.prism and grating monochromator are the most common Monochromator.vThe shortcomings of prism monochromator is th

10、at dispersion rate varies with wavelength,the spectra obtained were non uniformly arranged,and the light transfer efficiency is low.vgrating monochromator has a good and the same dispersion capacity almost in the whole spectral region . Therefore, the modern ultraviolet visible spectrophotometer usi

11、ng grating monochromator.入射狹縫：光源的光由此進入單色器； 準光裝置：透鏡或返射鏡使入射光成為平行光束； 色散元件：將復合光分解成單色光；棱鏡或光柵；聚焦裝置：透鏡或凹面反射鏡，將分光后所得單色光聚焦至出射狹縫； 出射狹縫。() sample room The sample chamber is placed in a variety of types of absorption pool (the ratio of the colored dishes) and the corresponding tank rack accessories. There are t

12、wo main types of the absorption pool, quartz and glass.Commonly,we should use the quartz pool in the UV visible region,and use the glass tank in the visible region .（四）檢測器（四）檢測器利用光電效應將透過吸收池的光信號變利用光電效應將透過吸收池的光信號變成可測的電信號。成可測的電信號。常用的檢測器有常用的檢測器有光電光電池、池、光電管和光電倍增管。光電管和光電倍增管。 （五）信號顯示器（五）信號顯示器 常用的顯示器有檢流計、微安

13、計、電位計、數(shù)常用的顯示器有檢流計、微安計、電位計、數(shù)字電壓表、記錄儀、示波器及數(shù)據(jù)處理機等。字電壓表、記錄儀、示波器及數(shù)據(jù)處理機等。二、儀器的類型 （一）Single-beam UV-Vis spectrophotometer光源光源單色器單色器參比參比樣品樣品檢測器檢測器顯示器顯示器 只有一條光路，通過變換參比池和樣品池的位只有一條光路，通過變換參比池和樣品池的位置，使它們分別置于光路來進行測定置，使它們分別置于光路來進行測定簡單，價廉，適于在簡單，價廉，適于在給定波長給定波長處測量吸光度或處測量吸光度或透光度，一般不能作全波段光譜掃描，要求透光度，一般不能作全波段光譜掃描，要求光光源源和

14、和檢測器檢測器具具有很有很高的穩(wěn)定性高的穩(wěn)定性。單色器參比樣品檢測器顯示器斬光器光源2.2.Double-beam 雙光束雙光束 自動記錄，自動記錄，快速全波段掃描快速全波段掃描?？上庠??？上庠床环€(wěn)定、檢測器靈敏度變化等因素的影響，特不穩(wěn)定、檢測器靈敏度變化等因素的影響，特別適合于結構分析。儀器復雜，價格較高別適合于結構分析。儀器復雜，價格較高。（三）（三）Double-wavelengthv一個光源，兩個單色器，一個吸收池一個光源，兩個單色器，一個吸收池光源單色器單色器吸收池檢測器斬光器用兩種不同波長的單色光束交替照射到樣品溶液上，不需使用參比溶用兩種不同波長的單色光束交替照射到樣品

15、溶液上，不需使用參比溶液，測得的是樣品在兩種波長下的吸光度之差液，測得的是樣品在兩種波長下的吸光度之差將不同波長的兩束單色光將不同波長的兩束單色光( (1 1、2 2) ) 快速交替快速交替通過同一吸收池而后到通過同一吸收池而后到達檢測器。產(chǎn)生交流信號。無需參比池。達檢測器。產(chǎn)生交流信號。無需參比池。 = = 1 12 2nmnm。A A=A=A2-A1=(2-1)bc=KcApplication of ultraviolet absorption spectrumQualitative and quantitative basisOrganic structure assisted anal

16、ysis1. qualitative analysisAt the same condition,It usually includes the determination of unknown material uv spectra, compared with the absorption spectrum of known standard material , analyzing the absorption spectral characteristics, such as absorption peak number, location, absorption valley, sh

17、oulder peak position, etc. If the molecular structure of the compounds is the same, they should have the same absorption spectra.Sample to be measured The same condiion The sample spectrumStandard material The standard spectrumAt a certain wavelength,the same substance in different concentrations At

18、 a certain wavelength,the same substance in different concentrations have the different absorbance A ,and the difference of absorbance at have the different absorbance A ,and the difference of absorbance at Max was the largest. This characteristic can be used as the basis Max was the largest. This c

19、haracteristic can be used as the basis for for quantitativequantitative analysis. analysis. 2.Quantitative analysis The basis:Lambert-Beers Law Lambert-Beers Law A= b c -lgT = b c high sensitivity： max：104105 L mol-1 cm -1； Generally,we measure A at the point of max in single component ,and then do

20、the standard curve to get the best sensitivity. The applicability of Lambert-Beers Law v The condition of Lambert-Beers Law establish is that the sample to be measured is homogeneous dilute solution, gas, etc.No solute, solvent and suspended matter caused by scattering; the incident light is monochr

21、omatic parallel light.vThe following circumstances do not set up or have a large deviation: 1.Not founded under the effection of chemical factors 2. Dissociation, association, the formation of complex or solvent, etc. caused deviation 3.Not founded under the effection of instrument factors.4.Non mon

22、ochromatic light caused deviation to the law.5.The clutter of scattered light (not the light) will cause an effect on the law.6.Other factors including solvent, light effect, etc. 2.Organic compound structure assistant analysis. 1. structural information from UV-Vis To understand the degree of conju

23、gation, the space effect, etc.,to determine the saturated and unsaturated compounds, isomers and conformation. The general rule of the information analysis of organic compound hair color system in the UV/Vis absorption spectra is: if there have no absorption peak within the wavelength range of 200 7

24、50nm ,it may be a straight chain alkanes, cycloalkanes, saturated aliphatic compounds or olefin containing only one double bond. if there have a low intensity absorption peak within the wavelength range of 270 to 350 nm(10100Lmol-1cm-1), (n* transition), it may contain a simple non conjugate and n-e

25、lectronic chromophore,such as carbonyl. 若在20300nm波長范圍內(nèi)有中等強度的吸收峰則可能含苯環(huán)，假設有精細結構的話，可能是苯環(huán)的特征吸收。 若在210250nm波長范圍內(nèi)有強吸收峰，則可能含有2個共軛雙鍵；若在260350nm波長范圍內(nèi)有強吸收峰，則說明該有機物含有3個或3個以上共軛雙鍵。 若該有機物的吸收峰延伸至可見光區(qū)，則該有機物可能是長鏈共軛或稠環(huán)化合物。2.光譜解析注意事項 (1) 確認max，并算出，初步估計屬于何種吸收帶； (2) 觀察主要吸收帶的范圍，判斷屬于何種共軛體系；三 .Purity check純度檢查v如果一化合物在紫外區(qū)如果

26、一化合物在紫外區(qū)沒有沒有吸收峰，而其中的吸收峰，而其中的雜質(zhì)有較強吸收雜質(zhì)有較強吸收，就可方便地檢出該化合物中，就可方便地檢出該化合物中的痕量雜質(zhì)。的痕量雜質(zhì)。v例如：要檢定甲醇或乙醇中的雜質(zhì)苯，可利用例如：要檢定甲醇或乙醇中的雜質(zhì)苯，可利用苯在苯在254nm處的處的B吸收帶，而甲醇或乙醇在此吸收帶，而甲醇或乙醇在此波長處幾乎沒有吸收。波長處幾乎沒有吸收。Application of ultraviolet absorption spectrumQualitative and quantitative basisOrganic structure assisted analysis1. qua

27、litative analysisAt the same condition,It usually includes the determination of unknown material uv spectra, compared with the absorption spectrum of known standard material , analyzing the absorption spectral characteristics, such as absorption peak number, location, absorption valley, shoulder pea

28、k position, etc. If the molecular structure of the compounds is the same, they should have the same absorption spectra.Sample to be measured The same condiion The sample spectrumStandard material The standard spectrumAt a certain wavelength,the same substance in different concentrations At a certain

29、 wavelength,the same substance in different concentrations have the different absorbance A ,and the difference of absorbance at have the different absorbance A ,and the difference of absorbance at Max was the largest. This characteristic can be used as the basis Max was the largest. This characteris

30、tic can be used as the basis for for quantitativequantitative analysis. analysis. 2.Quantitative analysis The basis:Lambert-Beers Law Lambert-Beers Law A= b c -lgT = b c high sensitivity： max：104105 L mol-1 cm -1； Generally,we measure A at the point of max in single component ,and then do the standa

31、rd curve to get the best sensitivity. The applicability of Lambert-Beers Law v The condition of Lambert-Beers Law establish is that the sample to be measured is homogeneous dilute solution, gas, etc.No solute, solvent and suspended matter caused by scattering; the incident light is monochromatic parallel light.vThe following circumstances do not set up or have a large deviation: 1.Not founded under the effection of chemical factors 2. Dissociation, association, the formati