布鲁克红外光谱培训1Introduction_to_FT-IR_c

1、,张远征01068474806-669 Zhang.yuanzheng,傅立叶红外光谱介绍,电磁波,Gamma Ray,X-Ray,UV,Infrared,Micro Wave,Short Wave,Radio Waves,Energy eV,Wavenumber cm-1,Wavelength m,Visible,光与分子的作用,分子激发产生振动,振动的种类?,伸缩振动,对称伸缩振动,不对称伸缩振动,例如: 水,变形振动,水的红外图,1500,2000,2500,3000,3500,wavenumber cm-1,60,65,70,75,80,85,90,95,10

2、0,Transmission %,正己烷,50多不同的振动,正己烷,指纹区“,红外光谱分为三个范围:,15.000 cm-1,4.000 cm-1,400 cm-1,5 cm-1,NIR,MIR,FIR,如何得到一张图,色散型红外光谱仪,傅立叶变换红外光谱仪,色散型红外光谱仪,Detector,Detector,优点: - 不需要计算机,缺点: - 速度慢 - 光通量低 = 灵敏度低 (S/N ratio),傅利叶变换红外光谱仪原理,x,Detector,x,L,L + x,例 1: x =0, 相长干涉,结果,1. Beam part (定镜),2. Beam part (动镜),x,L,L

3、 + x,例 2: x =1/2, 相消性干涉,0,结果,1. Beam part (定镜),2. Beam part (动镜),x,L,L + x,example 3: x = , constructive Interference,0,Resulting signal,1. Beam part (fixed),2. Beam part (movable),x,L,L + x,example 4: x =3/2, destructive Interference,0,Resulting signal,1. Beam part (fixed),2. Beam part (movable),Mi

4、rror motion,Intensity,监测器信号,Frequence,Intensity,光源,单色光源,单色光源的调制信号,Entstehung des Interferogramms,Frequence,Intensity,9条单一频率的光源,检测器信号,Frequency,Intensity,红外光源,X, moving mirror,Intensity,干涉图的来源,透射光谱,1.) In the empty sample compartment an Interferogram is detected. The result of the FOURIER transformat

5、ion is R().,Fourier-Transformation,500,1000,1500,2000,2500,3000,3500,4000,wavenumber cm-1,0.10,0.20,0.30,0.40,Single channel intensity,X, moving mirror,Detector intensity,2.) A second interferogram is detected with the sample placed in the sample compartment. The result of the FOURIER transformation

6、 is S(). S() shows similarities to the reference spectrum R(v), but has lower intensities at the regions the sample absorbs radiation.,Fourier-Transformation,500,1000,1500,2000,2500,3000,3500,4000,wavenumber cm-1,0.10,0.20,0.30,0.40,Single channel intensity,X, moving mirror,Detector intensity,透射光谱,T

7、he transmission spectrum T() is calculated as the ratio of the sample and reference single channel spectra: T() = S()/R().,透射光谱,Absorbance Transmission - Why?,Transmission,Absorbance,T() = S()/R(),Lambert-Beers law: AB = -log (S()/R() AB = c b,Principle layout of FT-IR spectrometer,x,Layout of an FT

8、-IR spectrometer (TENSOR series),Electronic,Source compartment,Sample compartment,Sample position,Detector,Interferometer compartment,Aperture wheel Filter wheel,NIR: Source : tungsten lamp Optical material : Quartz Detector: Ge, InGaAs MIR: Source: Globar Optical material: KBr, ZnSe Detector: DTGS,

9、 MCT FIR: Source : Globar, Hg lamp Optical material : PE, CsI Detector: DTGS, Bolometer,Differences between NIR, MIR, FIR,Optical components:,Fourier Transformation (FT),Data acquisition results in a digitized interferogram, I(x), which is converted into a spectrum by means of the mathematical opera

10、tion called a Fourier Transform (FT). The general equation for the Fourier Transform is applicable to a continuous signal. If the signal (interferogram) is digitized, however, and consists of N discrete, equidistant points, then the discrete version of the FT (DFT) must be used: S(k . ) = I(n x) exp

11、 (i2k n/N) The continuous variables x and have been replaced with n Dx and k D , representing the n discrete interferogram points and the k discrete spectrum points. The fact that we now have a discrete, rather than continuous, function, and that it is only calculated for a limited range of n (i.e.

12、the measured interferogram has a finite length) leads to important effects known as the picket-fence effect and leakage.,The Fourier Transform,x,高光谱分辨,低光谱分辨,添零,The picket-fence effect occurs if the interferogram contains frequency components which do not exactly coincide with the data point position

13、s, k. , in the spectrum. The effect can be thought of as viewing the spectrum through a picket fence, thereby hiding those frequencies that are behind the pickets, i.e. between the data point positions k. . In the worst case, if a frequency component is exactly between two sampling positions, a sign

14、al reduction of 36% can occur. The picket-fence effect can be reduced by adding zeros to the end of the interferogram (zero filling) before the DFT is performed. This interpolates the spectrum, increasing the number of points per wavenumber. The increased number of frequency sampling positions reduc

15、es the error caused by the picket-fence effect. Generally, the original interferogram size should always be at least doubled by zero filling, i.e. zero filling factor (ZFF) of two is chosen. Zero-filling interpolates using the instrument line-shape, and in most cases is therefore superior to polynom

16、inal or spline interpolation methods that are applied in the spectral domain.,Zero-filling factor 2,Zero-filling factor 8,截趾函数,In a real measurement, the interferogram can only be measured for a finite distance of mirror travel. The resulting interferogram can be thought of as an infinite length int

17、erferogram multiplied by a boxcar function that is equal to 1 in the range of measurement and 0 elsewhere. This sudden truncation of the interferogram leads to a sinc( ) (i.e. sin( )/ ) instrumental lineshape. For an infinitely narrow spectral line, the peak shape is shown at the top of the figure o

18、n the right. The oscillations around the base of the peak are referred to as “ringing”, or “leakage”. The solution to the leakage problem is to truncate the interferogram less abruptly. This can be achieved by multiplying the interferogram by a function that is 1 at the centerburst and close to 0 at

19、 the end of the interferogram. This is called apodization, and the simplest such function is a ramp, or “triangular apodization”. The choice of a particular apodization function depends on the objectives of the measurement. If the maximum resolution of 0.61/L is required, then boxcar apodization (i.

20、e no apodization) is used. If a resolution loss of 50% (compared to the maximum resolution of 0.61/L) can be tolerated, the HAPP-GENZEL or, even better, 3-Term BLACKMAN-HARRIS function is recommended.,A BOXCAR (no apodization),B Triangular,C Trapezoidal,D HAPP-GENZEL,E 3-TERM BLACKMAN-HARRIS,Evaluat

21、ion of IR spectra,定性分析： 1. 鉴定未知物 2. 核对已知物 定量分析,光谱评价,未知物的鉴定,a) 通过光谱解析推出分子结构,不同有几类分子的红外吸收,烷烃,烯烃,芳香烃,内酯,卤化物,羧酸盐,酸酐,b.) 与标准谱库比较 e.g. by using OPUS/Search,未知物的鉴定,identical material = identical IR spectrum - What you have: sample - What you need: reference library - What you do: comparison with reference

22、library - What you get: identification,验证已知物,2.) Calculate average spectrum & threshold values,3.) Library structure & validation,1.) Measure reference sample,Wavenumber / cm-1,Absorbance,Wavenumber / cm-1,Absorbance,Reference library structure,1.) Measure new samples,2.) Compare with library,Identi

23、fying new samples,3.) Identify material,- What you have: sample - What you need: calibration set - What you do: comparison with calibration set - What you get: concentration value There are two different forms of calibration: Univariate calibration (OPUS) - Correlates just one piece of spectral info

24、rmation (e.g. peak height or peak area) with the reference values of the calibration set. Multivariate calibration (OPUS/QUANT) - Correlates considerably more spectral information - higher degree of precision - reduced chance of error OPUS/QUANT uses the Partial Least Squares (PLS) Method.,Quantitative evaluation of spectra,2.) Build calibration set (Quant Method),3.) Validate calibration set,1.) Measure calibration spectra,W