Infrared spectrum, also known as vibrational rotation spectrum, is a molecular absorption spectrum.
When the molecule is irradiated by infrared light, it produces a transition of vibration energy level (accompanied by rotation energy level), accompanied by vibration (rotation).
If the dipole moment changes, it will absorb infrared photons and form an infrared absorption spectrum. Qualitative and qualitative analysis of substances can be carried out by infrared spectroscopy.
Quantitative analysis (mainly qualitative analysis) can identify the molecular structure of compounds from the characteristic absorption of molecules.
Fourier transform infrared spectrometer (FTIR), like other infrared spectrometers, is used to obtain substances.
Infrared absorption spectrum, but the determination principle is different. In a dispersive infrared spectrometer, the light emitted by a light source first illuminates a sample,
Then it is divided into monochromatic light by optical splitter (grating or prism) and detected by detector to obtain absorption spectrum. But in Fourier transform,
In infrared spectrometer, the light emitted by the light source is first changed into interference light by Michelson interferometer, and then the interference light illuminates the sample.
The interferogram is obtained by detector, and the absorption spectrum is obtained by Fourier transform of the interferogram by computer.
The infrared spectrum is divided into near infrared regions (13330-4000 cm) according to different wave number ranges.
- 1
), mid-infrared region (4000-650
centimetre
- 1
) and far infrared region (650- 10 cm.
- 1
)。 VECTOR22 VECTOR22 FTIR spectrometer provides analysis in the mid-infrared region.
Just try it.
Two. Sample preparation
1. Requirements for samples
(1) The sample should be a single-component pure substance.
(2) The sample should not contain free water.
(3) The concentration or test thickness of the sample should be appropriate.
2. Sample preparation method
(1) gas sample
When using the gas chamber, the air in the chamber should be pumped out first, and then the gas sample to be measured should be inhaled.
(2) Liquid samples
Commonly used methods are liquid membrane method and liquid pool method.
Liquid membrane method:
Samples with higher boiling point can be directly dropped between two pieces of KBr salt to form a liquid film for testing. Take two pieces of KBr salt.
Sheet, wash its surface with acetone cotton and air dry. Drop 1 drop of sample on one salt tablet, press another salt tablet on it, and then load.
Go to the detachable liquid sample test rack for determination. After scanning, take out the salt tablets and wipe them clean with acetone cotton.
Put it back in the dryer for preservation. High viscosity samples can be directly coated on salt tablets for determination. You can also press it with KBr powder.
Ingots replace salt tablets.
Z attention
Salt tablets absorb water easily, so you need to wear finger covers when taking salt tablets.
After the salt tablet is put into the liquid sample test rack, the screw should not be tightened too tightly to avoid crushing the salt tablet.
Liquid pool method:
Samples with low boiling point and high volatility or samples with low viscosity and high fluidity can be injected and sealed.
When testing in a liquid pool, the thickness of the liquid layer is generally 0.0 1- 1 mm ... Some pure liquid samples with strong absorption, if in
After reducing the thickness of the liquid pool, a good spectrum can not be obtained, and it can be prepared into a solution for testing. The liquid pool should be cleaned and dried in time.
Clean, don't let it be polluted.
(3) Solid samples
Commonly used methods include tabletting, paraffin paste and film method.
1 FTIR operation manual of intermediate instrument laboratory of Peking University Institute of Chemistry.
Tablet pressing method:
Generally, the ingot for infrared measurement is a small piece with a diameter of 13mm and a thickness of about1mm. Take a sample (about 1mg) and dry it.
Mix KBr (about 200mg) evenly in agate mortar, fully grind it (the particle reaches about 2μm), and mix evenly.
Uniformly placing the compound between the upper die and the lower die of the solid tabletting die, and then putting the die into a press with a pressure of 8T/cm.
2
Keep it at left and right pressure for 1-2 minutes to obtain a transparent or even translucent ingot. Take out the ingot and fill it with solids.
On the sample test rack.
Z attention
Potassium bromide is very corrosive to the surface of steel mold, so the mold must be cleaned in time after use and then put into the dryer.
Medium.
Samples that are easy to absorb water and deliquesce are not suitable for tabletting.
After the mold is put into the press, the top valve should be rotated to make the pressure bar close to the mold, and then the air release valve should be closed. Small amplitude
Pull the wrench to make the pressure reach 8T/ cm.
2
Hold for 1-2 minutes. When opening the air valve, the rotation range cannot exceed.
30
! !
Z hint
For the sample that is difficult to grind, it can be dissolved in a few drops of volatile solvent and then mixed with potassium bromide powder to form a paste.
After grinding until the solvent is completely volatilized, the residual solvent can also be driven away under the infrared lamp.
For elastic samples such as rubber, they can be embrittled at low temperature (-40℃) and then mixed with potassium bromide powder for grinding.
Paraffin paste method:
Grind the dried sample, mix it with liquid paraffin or perfluorohydrocarbon, make it into paste, and put it into salt tablets for measurement.
Just try it.
Thin film method:
The thin film made of solid samples can avoid the interference of matrix or solvent on the sample spectrum, and the thickness of the thin film is
10-30μm with uniform thickness. Thin film method is mainly used for the determination of polymer compounds, for some low melting points and low fractions.
Subcompounds can also be used. They can be directly heated and melted, and then coated or pressed into films, or the samples can be dissolved at a low boiling point.
Dot it in volatile solvent, coat it on salt, and determine it after the solvent evaporates into a film.
Three. Light-transmitting material in mid-infrared region
Material name chemical composition light transmission range (cm
- 1
) solubility in water (g/ 100mL) refractive index
Sodium chloride NaCl 5000-625 35.7 1.54
Potassium bromide KBr 5000-400 53.5 1.56
Cesium iodide CSI 5000-165 44.01.79
KRS-5 TlBr，TlI 5000-250 0.02 2.37
Silver chloride AgCl 5000-435 Insolubility 2.0
Silver bromide AgBr 5000-285 Insolubility 2.2
ba F2 5000-830 0. 17 1.46
Calcium fluoride caf25000-1100 0.05438+061.43
Zinc sulfide is insoluble in 2.2.
Zinc selenide ZnSe 5000-500 Insolubility 2.4
diamond
(Ⅱ)
c 3400-2700； 1650-600 Insolubility 2.42
Germanium Ge 5000-430 Insolubility 4.0
Silicon Si 5000-600 insoluble 3.4
2 FTIR operation manual of intermediate instrument laboratory of Peking University Institute of Chemistry
Four. Introduction of Vector 22 FTIR spectrometer
VECTOR 22 FTIR spectrometer is manufactured by Bruker Company in Switzerland. It consists of an optical table, a computer and a printer.
Spectral range: 7500-370 cm
- 1
Resolution: 1cm
- 1
Signal to noise ratio: 5500: 1
Wave number accuracy: 0.0 1cm
- 1
Infrared light source: Globar (high intensity air-cooled light source)
Interferometer: myerson interferometer (30
Accident Rocksolid patented technology)
Beam splitter: germanium plating on KBr
Detector: DTGS (deuterated sulfate tripeptide)
Schematic diagram of optical path of VECTOR 22 FTIR optical table
A- infrared light source B- aperture/film wheel C- exit D- beam splitter
E.E
'
-window F- sample rack G- detector
When using infrared spectrometer, please keep the room clean and dry, and don't shake the optical table. Cover the sample when taking and placing it.
It should be opened and closed gently. If the test parameters change, please make a record and recover after the test. Besides, don't look at the He-Ne excitation.
Light, so as not to get hurt.
3 FTIR operation manual of intermediate instrument laboratory of Peking University Institute of Chemistry
Operation and software application of VECTOR 22 FTIR spectrometer
(a) boot, shutdown
Turn on the power: Optical table open
. The computer is turned on (no password has been set for this computer)
Left-click OPUS shortcut key
. Enter the password: OPUS (capital letters)
. User ID: select the administrator.
. Assigned Workspace: Do not modify.
. Click Login.
Click the left OK to enter the OPUS user interface window (as shown in the figure below).
Close:. Shut down the computer after closing all windows of the computer.
The optical table is closed.
(b) Introduction of OPUS user interface
(The drop-down menu of all functions of OPUS software.
(b) Shortcut icons for frequently used functions.
(c) OPUS file management window, similar to Windows browsing window.
(d) spectrogram display window.
(e) Overview window, which always displays the spectrogram of the entire frequency range of the selected data file.
(f) online help.
(g) The status bar displays tasks running in the background.
(h) Instrument status indication.
4 FTIR operation manual of intermediate instrument laboratory of Peking University Institute of Chemistry
1.OPUS browsing window
When measuring a generated file or an open OPUS file, its file name, data block and file status information are displayed in.
Browse window (left side of the screen). When the cursor is placed on the file name, the complete path of the data will be displayed; The cursor is placed on the data block,
Displays the operator name, sample name and sample shape.
(a) Click to reduce the corresponding spectrogram window.
(b) Blue indicates that the document has not been processed. The number after the filename is the number of copies of the file.
(c) All data blocks saved with the file. The icons in the figure indicate transmission spectrum, single channel spectrum, single channel spectrum and single channel spectrum.
Interferogram and single channel background spectrum. If the data block is colored, it indicates that the corresponding spectrogram is being displayed in the spectrogram window.
Click the right mouse button on the file name to pop up the file operation menu:
Save File: Any processing of the file will not be automatically saved to the file. Click Save File to save the file.
Unload file: Close the file.
Undo all operations: Undo all processing of files.
Display parameters: display the corresponding parameters and information of the file.
Copy entry: Copy the entire file, including processing.
Clone original file: copy only the original file.
5 FTIR operation manual of intermediate instrument laboratory of Peking University Institute of Chemistry
2.Opus spectrogram window
The spectrogram window is located on the right side of the OPUS user interface. When the measurement is completed or the file is transferred in, the spectrogram will be displayed.
The default spectrogram display area is 4000 ~ 400 cm.
- 1
The absorbance unit is 0- 1.5. By displaying-zooming all or one.
Click the icon to display the complete spectrum.
Right-click the mouse on the spectrum line of the spectrum window, and the menu shown below will appear, which can enlarge and reduce the spectrum and change the display of the spectrum.
Range, add labels, change the color of spectral lines, etc. Click the right mouse button in the blank area of the spectrogram window, and a similar menu will appear with slightly different functions.
Less.
Zoom in: Loud spectrogram. Hold down the left mouse button and drag the crosshairs. After framing the part to be enlarged, click Enlarge.
Select: Zoom All Spectra/Show All Contents (xy) from the right-click menu to restore to full scale.
Inch spectrogram.
Shrink: reduce the spectrum. The operation method is the same as above.
Zoom All Spectra-Show Everything (xy), showing all spectra in the full range.
Maximize each spectrum (y): Maximize the y coordinate of each spectrum.
Moving curve: moving the whole spectrogram along the Y axis or enlarging or reducing the spectrogram in one direction. Hold down the left mouse button and drag the spectrogram to move.
Or zoom. Right-click to cancel this function. Reset can be restored.
Cross cursor: cursor, which can move freely in the atlas area and display the X and Y coordinates of the corresponding point.
Following the data, the cursor only moves along the spectral line, so it is easy to read the X and Y coordinates of any point on the spectrum.
Click the right mouse button to cancel this function.
Change color: change the color of the spectrogram.
Delete from Display: Deletes the spectrogram from the spectrogram window.
Add comments: Add comments. Clicking on the spectrogram will add an arrow at the cursor position, and the wave number at this point will be displayed by default.
Move the label: hold down the left mouse button and drag the label.
To delete a tag: right-click the tag and select Delete from the menu.
Edit Label: Right-click the label and select Properties. Enter or edit dimensions.
Attribute: Set the abscissa and ordinate of spectrogram.
6 FTIR operation manual of intermediate instrument laboratory of Peking University Institute of Chemistry
(3) spectrogram test
Test spectral measurement → advanced measurement
1 On the basic page, enter:
Operator's name, sample name and sample form; .
2 On the advanced page, enter:
filename
File saving path (this path is defined as: d:/ data/tutor's name/student's name/), which can be entered or called out.
Resolution (the resolution is set to 4cm
- 1
, please do not modify)
Sample scanning or sample scanning time (minutes)
Background scanning time (scanning) or sample scanning time (minutes)
Spectral test range (for mid-infrared instruments, the setting range is usually: 4000 ~ 400 cm.
- 1
(
Other options are general settings and cannot be changed.
The other six pages (from optics to inspection signal) should not be modified.
4 Place a reference object (or air as background) in the sample room.
On the basic page, click the background single channel to test the background.
5 put the sample into the sample room.
On the Basic page, click the sample single channel to test the sample.
(Note: The above settings can be saved as a method file: click Save, select a save path, and enter a file name.
The suffix of the file name should be. XPM。 When testing in the future, just load it into the advanced page and you can call it up. )
(4) display spectrogram
Displays the file name, data block and file status information of the file generated after the measurement is completed or the OPUS file is opened.
It is displayed in the browse window (the small window on the left side of the screen). When the cursor is placed on the file name, the full path of the file will be displayed; cursor position
On the data block, the operator name, sample name and sample form are displayed.
The corresponding atlas is displayed in the spectrogram window (in the right window of OPUS user interface). The default spectrogram display area is
4000 ~ 400 cm
- 1
The absorbance unit is 0- 1.5. Display by Display-Zoom All or click the icon.
Display the full spectrum.
Right-click the mouse on the spectrum line of the spectrogram window, and a menu will appear. You can zoom in and out the spectrogram, change the display range of the spectrogram, and add.
Add labels, change the color of spectral lines, etc. Right-click the mouse in the blank area of the spectrogram window, and a similar menu appears, with slightly less functions. tool
For the operation of the machine body, please refer to the relevant introduction on page 6 of this manual.
(5) spectrogram processing
When realizing various spectrogram processing functions, there is a "Select File" page, which displays the currently selected spectrogram by default.
File name (spectrogram file with red box in the browsing window). To add a file, you can browse the required spectrogram in the window.
Select and drag data blocks (usually absorption spectrum data blocks or transmission spectrum data blocks). To delete files, please select Chinese.
After the name, press the "Delete" key on the keyboard.
1 baseline correction operation → baseline correction
Select spectrogram (baseline correction can be performed on multiple spectrograms at the same time), and then select correction method and correction point.
Correct. The corrected spectrogram automatically overwrites the original spectrogram.
Scattering correction: the corrected baseline basically falls at 0 or 100%.
Rubber band correction: after correction, some baselines may not fall at 0 or 100%.
7 FTIR operation manual of intermediate instrument laboratory of Peking University Institute of Chemistry
Exclude CO2 band: deduct CO2 band. Select this option to adjust the baseline of the band containing CO2.
(2400~2275cm
- 1
、680~660cm
- 1
) it doesn't count.
2 Standard peak position evaluation → peak pick-up
Select the spectrogram and the spectral area to be marked, set the sensitivity (peak threshold), click on the peak selection, and the spectrogram will
Displays the peak position.
You can also choose interactive mode to mark peaks: click interactive mode and drag the threshold slider, and the number of marked peaks will increase.
Increase or decrease with the change of threshold, so as to determine the appropriate threshold. Click the store to complete the peak marking.
3 spectral subtraction operation → spectral subtraction
Select the spectrum to be subtracted and the subtracted spectrum (you can select one or more subtracted spectra), select the spectrum area, and point out the subtraction. Obtained difference spectrum
The subtracted spectrum will be overwritten.
If you choose to start interactive mode, you can set different coefficients by time and changing numbers.
Difference spectrum = subtraction spectrum-coefficient x subtraction spectrum
Click Save to complete the differential spectrum. Several spectrograms can be subtracted separately.
4 AB & lt-& gt； TR conversion operation → ab
Conversion between transmission spectrum and absorption spectrum. Select the spectrogram, select the conversion direction, and click the conversion. New spectrum
The map will overwrite the original spectral map.
5 generate linear manipulation → linear conversion
Generate a straight line command to eliminate some special interference in the spectrogram. Select spectrogram, set frequency range, point
The spectral lines in this frequency range in the spectrogram become straight lines.
6 Smooth manipulation → Smooth
Select the spectrogram, define the number of smoothing points, and then click Smoothing. Optional values for smoothing points are 5 to 25. You can also use interactive mode.
Smooth spectrogram.
8 FTIR operation manual of intermediate instrument laboratory of Peking University Institute of Chemistry
7 derivative operation → derivative
Select spectral file, smoothing point and derivative order, and click "Process" to generate derivative file. The derivative spectrum is shown in the original.
Below the spectrogram.
The first to fifth derivatives of the spectrogram can be calculated. Derivative can also smooth the spectrum to reduce the noise caused by derivative. that
The minimum number of smoothing points depends on the order of derivation. The higher the order of the derivative, the more points should be set. 25 o'clock is allowed at most.
8 1/cm & lt； -& gt； ? M, nm manipulation →1/cm <; -& gt； ? Rice, nanometer
Change the abscissa unit.
9 overall integration
Calculate peak area and peak height. There are 18 integration methods.
10 normalization operation → normalization
This function is used to normalize spectrogram and offset correction.
Select the file and frequency range to normalize, select the method, and then click Normalize.
There are three standardization methods:
(1) min/max normalization-(min/max normalization): the minimum value of the spectrogram becomes 0, y.
The maximum value of the axis is extended to 2 absorption units. Normalize the transmission spectrum to the range of 0 to 1.
(2) Vector Normalization-(Vector Normalization): First, calculate the average value of the frequency spectrum, and then
Subtract the average value from the spectrogram, so the middle of the spectrogram is pulled down to 0; Calculate the square of all y values at this time
The square root of the sum. Divide the original spectrum by this square root value. Vector modulus of spectrogram processed in this way.
It is 1.
(3) Offset correction —— Move the spectrogram to make the minimum y value move to the absorption value of 0.
1 1. atmospheric compensation operation → atmospheric compensation.
When measuring the background or sample spectrum, the difference of H2O/CO2 concentration in the optical path will cause the change of H2O/CO2 band intensity.
Change. The atmosphere compensation function can eliminate the interference of H2O/CO2 in the ratio spectrum.
In addition to absorbing (or transmitting) data blocks, the atlas file to be compensated for atmosphere should also contain a single.
Channel sample block and single channel background block (before testing, it should be in
In Measurement → Advanced Measurement, add single channel and background.
Save by block).
Select operation → atomic compensation to process spectrogram signal.
The channel sample block and the single channel reference block are respectively dragged into corresponding regions,
Select H2O Compensation and CO2 Compensation, and then click Calculate.
9 FTIR operation manual of intermediate instrument laboratory of Peking University Institute of Chemistry
(6) Printing and photocopying
1. Print spectrogram Print → Print spectrogram
Select the spectrogram and related data blocks (such as peak data blocks) to be printed.
Click Change Layout and select Atlas Print Template. Commonly used templates are:
Landscape- 1, A4 paper, a spectral frame, horizontally punched;
Vertical -2, A4 paper, two spectral frames, vertical printing
Vertical-3,A4 paper, three spectral frames, vertical printing
Set the spectrogram printing interval within the frequency range;
In the options, you can choose to automatically zoom to all spectra to enlarge all spectra to be printed.
Show. In addition, by default, the x-axis of the spectrum is a linear coordinate. To use compressed coordinates, you can choose to use compressed coordinates.
Wavenumber, abscissa 2000 cm- 1 or above will be compressed twice.
It should be noted that if the atlas printing template includes more than one frame, such as Portrait-3, a piece of A4 paper.
Print three independent spectrograms. At this time, the spectrogram to be printed in each spectrogram box should be selected separately. system of selection
Used to: select the name of the spectral box in the frame drop-down box, and select the file to be printed in the spectral box in the file selection. rely on
The second operation is to select the spectrogram to be printed in each spectrogram box.
You can click Preview at any time during the installation. After the preview is correct, click Print to print.
2. Data copy file → Save file as
Convert atlas files into data files and copy them directly. You must use a new floppy disk.
On the "Select File" page, select the file to save and enter the save as path A\ (or select it in the change path.
Select) and file name.
Select the date point table on the mode page.
Click Save to finish.
10 FTIR operation manual of intermediate instrument laboratory of Peking University Institute of Chemistry.
Eight. Introduction of Attenuated Total Reflection Accessories
(1) Principles and characteristics
Attenuated total reflection spectrum (ATR) is also called internal reflection.
Internal reflection spectrum. There are two conditions for total reflection: light enters from an optically dense medium.
Only when light enters the hydrophobic medium will total reflection occur; The incident angle should be greater than the critical angle. The phenomenon of total reflection is not completely divided into two types.
At the interface of the medium, part of the light beam will enter the light-hydrophobic medium for a certain distance and then be reflected back. Penetrating light
With the increase of penetration depth, the beam intensity with hydrophobic medium decreases exponentially.
ATR spectrum has the following characteristics:
(1) infrared radiation is absorbed by the interaction between samples, so ATR spectrum has transmission absorption.
The characteristics and shape of the spectrum, but due to the different sensitivity of ATR technology in different wave number intervals, ATR spectrum absorbs
Compared with the transmission spectrum, the relative intensity of peak reception is not completely consistent.
(2) The nondestructive analysis method can keep the original determination.
(2) Testing
1.Installation and adjustment of ATR accessories
(1) Select the energy of the spectrometer by adjusting the interferometer.
(2) Install ATR accessories on the spectrometer with two fixed knobs.
(3) Carefully adjust the relative position of the accessory and the laser output of the spectrometer to obtain the maximum output.
(4) Fix ATR accessories with the fixing knob.
2. Preparation of samples
Infrared absorption spectrum is obtained by subtracting the background light of the sample and the sample on the crystal. Pay attention to ensure that the sample is completed.
Completely covering the crystal surface. ATR crystal is made of ZnSe, which is fragile and easy to scratch. Even a slight scratch.
It will also cause the signal output to drop. Therefore, it is necessary to use a mild detergent, such as ethanol, acetone or water.
Solid samples and powder samples are directly placed on ATR crystal and pressed with the attached fixing clips. Compacted with gold.
Tighten the pin to ensure close contact between the sample and the crystal.
Liquid samples are suitable for liquids with low viscosity. The viscous liquid should be completely spread on the crystal surface.
2. Spectral scanning and data processing are the same as general infrared spectrum.