紫外光谱分析-演讲

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, 各种溶液之所以呈现不同的颜色, 与它对光的选择性吸收

2、有关。当一束由各种波长按一定比例组成的光透过一溶液时, 某些波长的光被溶液吸收, 而另一些波长的光不被吸收而透过溶液。当透过的光包含有可见光波长范围内的光时, 就可以被人眼察到, 溶液的颜色正是由透过光的波长所决定。 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*分子中电子的能级和跃迁 2. nss* transition 实现这类跃迁所需要的能量实现这类跃迁

4、所需要的能量较高，较高， 吸收波长为吸收波长为150250nm，大部分在远紫外区，大部分在远紫外区，近紫外区仍不易观察到。近紫外区仍不易观察到。 含非键电子的饱和烃衍生物含非键电子的饱和烃衍生物(含含N、O、S和卤素等杂原子和卤素等杂原子)均均呈现呈现n* 跃迁。如跃迁。如CH3OH4. npp* transition 这类跃迁发生在近紫外光区这类跃迁发生在近紫外光区, 一般一般200 nm 。它是简单的生色。它是简单的生色团如团如羰基羰基、硝基等中的孤对电子、硝基等中的孤对电子向反键轨道跃迁。其特点是向反键轨道跃迁。其特点是谱带谱带强度弱强度弱，摩尔吸光系数，摩尔吸光系数小小，通常，通常小于

5、小于100，属于禁阻跃迁。，属于禁阻跃迁。-OH AACCCCCCCCCH3CH3 超共轭效应比共轭效应的影响小的多超共轭效应比共轭效应的影响小的多CCHHCCHH反式反式 大共轭体系大共轭体系 顺式顺式* n* * n*分子中电子的能级和跃迁 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.入射狭缝：光源的光由此进入单色器； 准光装置：透镜或返射镜使入射光成为平行光束； 色散元件：将复合光分解成单色光；棱镜或光栅；聚焦装置：透镜或凹面反射镜，将分光后所得单色光聚焦至出射狭缝； 出射狭缝。() 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）检测器（四）检测器利用光电效应将透过吸收池的光信号变利用光电效应将透过吸收池的光信号变成可测的电信号。成可测的电信号。常用的检测器有常用的检测器有光电光电池、池、光电管和光电倍增管。光电管和光电倍增管。 （五）信号显示器（五）信号显示器 常用的显示器有检流计、微安

13、计、电位计、数常用的显示器有检流计、微安计、电位计、数字电压表、记录仪、示波器及数据处理机等。字电压表、记录仪、示波器及数据处理机等。二、仪器的类型 （一）Single-beam UV-Vis spectrophotometer光源光源单色器单色器参比参比样品样品检测器检测器显示器显示器 只有一条光路，通过变换参比池和样品池的位只有一条光路，通过变换参比池和样品池的位置，使它们分别置于光路来进行测定置，使它们分别置于光路来进行测定简单，价廉，适于在简单，价廉，适于在给定波长给定波长处测量吸光度或处测量吸光度或透光度，一般不能作全波段光谱扫描，要求透光度，一般不能作全波段光谱扫描，要求光光源源和

14、和检测器检测器具具有很有很高的稳定性高的稳定性。单色器参比样品检测器显示器斩光器光源2.2.Double-beam 双光束双光束 自动记录，自动记录，快速全波段扫描快速全波段扫描。可消除光源。可消除光源不稳定、检测器灵敏度变化等因素的影响，特不稳定、检测器灵敏度变化等因素的影响，特别适合于结构分析。仪器复杂，价格较高别适合于结构分析。仪器复杂，价格较高。（三）（三）Double-wavelengthv一个光源，两个单色器，一个吸收池一个光源，两个单色器，一个吸收池光源单色器单色器吸收池检测器斩光器用两种不同波长的单色光束交替照射到样品溶液上，不需使用参比溶用两种不同波长的单色光束交替照射到样品

15、溶液上，不需使用参比溶液，测得的是样品在两种波长下的吸光度之差液，测得的是样品在两种波长下的吸光度之差将不同波长的两束单色光将不同波长的两束单色光( (1 1、2 2) ) 快速交替快速交替通过同一吸收池而后到通过同一吸收池而后到达检测器。产生交流信号。无需参比池。达检测器。产生交流信号。无需参比池。 = = 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波长范围内有中等强度的吸收峰则可能含苯环，假设有精细结构的话，可能是苯环的特征吸收。 若在210250nm波长范围内有强吸收峰，则可能含有2个共轭双键；若在260350nm波长范围内有强吸收峰，则说明该有机物含有3个或3个以上共轭双键。 若该有机物的吸收峰延伸至可见光区，则该有机物可能是长链共轭或稠环化合物。2.光谱解析注意事项 (1) 确认max，并算出，初步估计属于何种吸收带； (2) 观察主要吸收带的范围，判断属于何种共轭体系；三 .Purity check纯度检查v如果一化合物在紫外区如果

26、一化合物在紫外区没有没有吸收峰，而其中的吸收峰，而其中的杂质有较强吸收杂质有较强吸收，就可方便地检出该化合物中，就可方便地检出该化合物中的痕量杂质。的痕量杂质。v例如：要检定甲醇或乙醇中的杂质苯，可利用例如：要检定甲醇或乙醇中的杂质苯，可利用苯在苯在254nm处的处的B吸收带，而甲醇或乙醇在此吸收带，而甲醇或乙醇在此波长处几乎没有吸收。波长处几乎没有吸收。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