What Is IR Spectroscopy Instrumentation?

Infrared spectrometer is an instrument for analyzing the molecular structure and chemical composition by utilizing the absorption characteristics of substances to infrared radiation of different wavelengths. An infrared spectrometer usually consists of a light source, a monochromator, a detector, and a computer processing information system. According to the different spectroscopic devices, they are divided into dispersion type and interference type. For a dispersion-type dual-optical optical zero-balance infrared spectrophotometer, when a sample absorbs infrared radiation of a certain frequency, the vibrational energy level of the molecule changes, and the light of the corresponding frequency in the transmitted beam is weakened, causing a reference. The intensity of the corresponding radiation of the optical path and the sample optical path is different, thereby obtaining the infrared spectrum of the measured sample.

infrared spectrometer

Infrared spectrometer is an instrument for analyzing the molecular structure and chemical composition by utilizing the absorption characteristics of substances to infrared radiation of different wavelengths. An infrared spectrometer usually consists of a light source, a monochromator, a detector, and a computer processing information system. According to the different spectroscopic devices, they are divided into dispersion type and interference type. For a dispersion-type dual-optical optical zero-balance infrared spectrophotometer, when a sample absorbs infrared radiation of a certain frequency, the vibrational energy level of the molecule changes, and the light of the corresponding frequency in the transmitted beam is weakened, causing a reference. The intensity of the corresponding radiation of the optical path and the sample optical path is different, thereby obtaining the infrared spectrum of the measured sample.

Chinese name

infrared spectrometer

Foreign name

infrared spectrometer

Application range

Industry, agriculture, medicine, science, military

Principle

Absorption of infrared radiation of different wavelengths by substances

The infrared part of the electromagnetic spectrum can be divided into near-infrared, mid-infrared, and far-infrared light according to its relationship with the visible spectrum. Far infrared light (approximately 400-10 cm-1) is adjacent to the microwave and has low energy, which can be used for rotational spectroscopy. Mid-infrared light (approximately 4000-400 cm-1) can be used to study basic vibrations and related rotational-vibration structures. Higher energy near-infrared light (14000-4000 cm-1) can excite

The Fourier transform infrared spectrometer is called the third generation infrared spectrometer. It uses a Michelson interferometer to interfere the two colored infrared light beams whose optical path difference changes at a certain speed to form interference light, and then interacts with the sample. The detector sends the interference signal obtained

Generally divided into two categories, one is raster scanned and rarely used; the other is scanned by Michelson interferometer, called Fourier transform infrared spectrum, which is currently the most widely used. The raster scan uses a spectroscope to divide the detection light (infrared light) into two beams, one as the reference light and the other as the detection light to illuminate the sample. Then the grating and the monochromator are used to separate the wavelengths of the infrared light, scan and detect one by one The intensity of the wavelength is finally integrated into a spectrum. Fourier transform infrared spectroscopy uses a Michelson interferometer to separate the detection light (infrared light) into two beams, which are reflected back to the beam splitter on a moving mirror and a fixed mirror. These two beams of light are broadband coherent light and will interfere. Coherent infrared light is irradiated on the sample and collected by the detector to obtain infrared interferogram data containing the sample information. After the data is Fourier transformed by a computer, the infrared spectrum of the sample is obtained. Fourier transform infrared spectroscopy is widely used because of its fast scanning rate, high resolution, and stable repeatability. ^[1]

Used in dyeing and weaving industry, environmental science, biology, materials science, polymer chemistry, catalysis, coal structure research, petroleum industry, biomedicine, biochemistry, pharmacy, basic research of inorganic and coordination chemistry, semiconductor materials, daily chemical industry And other research areas.

Infrared spectroscopy can study the structure and chemical bonds of molecules, such as the determination of force constants and molecular symmetry. The infrared spectroscopy method can be used to determine the molecular bond length and bond angle, and to speculate the three-dimensional configuration of the molecule. The strength of the chemical bond can be inferred from the obtained force constant, and the thermodynamic function can be calculated from the normal frequency. Some groups of molecules or chemical bonds in the corresponding band wave number of different compounds are basically fixed or only change in a small range, so many organic functional groups such as methyl, methylene, carbonyl, cyano, Hydroxyl groups, amine groups, etc. all have characteristic absorption in the infrared spectrum. Through infrared spectrum measurement, one can determine which organic functional groups exist in the unknown sample, which lays the foundation for the final determination of the chemical structure of the unknown.

Due to intra- and inter-molecular interactions, the characteristic frequencies of organic functional groups will change slightly due to the different chemical environments in which the functional groups are located, which creates conditions for the study of characterization of intra- and inter-molecular interactions.

Many normal vibrations of molecules in the low wavenumber region often involve all the atoms in the molecule. Different molecules vibrate differently from each other, which makes the infrared spectrum as highly characteristic as a fingerprint, called the fingerprint region. Using this feature, people have collected the infrared spectra of tens of thousands of known compounds and stored them in a computer to compile a library of standard spectra of infrared spectra.

One only needs to compare the infrared spectrum of the unknown with the spectrum in the standard library to quickly determine the composition of the unknown compound.

The development of contemporary infrared spectroscopy technology has made the significance of infrared spectroscopy far beyond the stage of performing simple routine tests on samples and inferring the composition of compounds. The combination of infrared spectrometer and many other testing methods has led to many new molecular spectroscopy fields. For example, the combination of chromatography technology and infrared spectrometer has created an opportunity to deepen the understanding of the chemical structure of various components in a complex mixture system. The combination of the microscopy method and the infrared imaging technology is used to study the morphological structure of the heterogeneous system. The infrared spectrum can use its characteristic band to effectively distinguish different compounds, which makes this method have a chemical contrast that is unmatched by other methods.

The use of infrared spectrometer for qualitative analysis of materials is widely used in major universities, colleges, scientific research institutes and factories and mines. Common institutions with infrared spectrometer detection capabilities are: Sichuan University, Southwest Jiaotong University, Zhonglan Chenguang Chemical Research Institute, Huatong Special Engineering Plastics Research Center, etc.

Perform identification of compounds Perform structural analysis of unknown compounds

Quantitative analysis of compounds for chemical reaction kinetics, crystal transitions, phase transitions, material transients and structural transient relationships

Continuous detection of industrial processes and air pollution

Monitoring of free silica in the coal industry

Inspection of jewellery industry in many fields such as health quarantine, pharmaceuticals, food, environmental protection, public security, petroleum, chemical industry, optical coating, optical communication, materials science, etc.

Crystal quartz hydroxyl measurement polymer composition analysis drug analysis ...

1. Only three beam splitters can cover the range from ultraviolet to far infrared;

2. Patented interferometer, continuous dynamic adjustment, extremely high stability;

3. It can realize the combined use of LC / FTIR, TGA / FTIR, GC / FTIR and other technologies;

4. Intelligent accessories are plug-and-play, automatic identification, and automatic adjustment of instrument parameters;

5. The integrated design of the optical table, the main component is positioned on the needle, no adjustment is needed.

Perform identification of compounds Perform structural analysis of unknown compounds

Quantitative analysis of compounds for chemical reaction kinetics, crystal transitions, phase transitions, material transients and structural transient relationships

Continuous detection of industrial processes and air pollution

Monitoring of free silica in the coal industry

Inspection of jewellery industry in many fields such as health quarantine, pharmaceuticals, food, environmental protection, public security, petroleum, chemical industry, optical coating, optical communication, materials science, etc.

Crystal quartz hydroxyl measurement polymer composition analysis drug analysis ...

1. The temperature of the laboratory should be 15-30 ° C, and the relative humidity should be below 65%. The power supply should be equipped with a voltage stabilizer and a ground wire. Because the relative humidity in the room must be strictly controlled, the area of the infrared laboratory should not be too large, and the necessary equipment can be placed, but the room must have a dehumidification device ^[2] .

2. If you are using a single photon-type Fourier infrared spectrophotometer (currently the most widely used), the CO2 content in the laboratory must not be too high, so the number of people in the laboratory should be as small as possible, and unrelated personnel should not enter. Also pay attention to proper ventilation.

3. If the test product is hydrochloride, due to the possible ion exchange phenomenon in the tabletting process, the standard stipulates that potassium chloride (also used after pretreatment like potassium bromide) is used instead of potassium bromide for compression. Tablets, but the spectra measured after potassium chloride tableting and potassium bromide tableting can also be compared. If there is no difference between the two, then potassium bromide can be used for tabletting.

4. In order to prevent the life of the instrument from being affected by moisture, the infrared laboratory should always be kept dry. Even if the instrument is not used, it should be turned on at least twice a week for half a day each time, and the dehumidifier should be turned on at the same time. Especially in the mildew rain season, it is best to turn on the dehumidifier every day.

5. The most commonly used sample preparation method for infrared spectroscopy measurement is the potassium bromide (KBr) tablet method (used by more than 90% of the pharmacopoeial varieties), so in order to reduce the impact on the measurement, the KBr used should preferably be optical Reagent grade, at least analysis of pure grade. Before use, it should be properly ground (200 mesh or less), and dried at 120 ° C for 4 hours or more in a dryer. If lumps are found, they should be re-dried. The prepared empty KBr sheet should be transparent, and the light transmittance should be more than 75% compared with air.

6. The test sample used in the tableting method is generally 1 to 2 mg. Because it is impossible to add it after weighing with a balance, and the degree of absorption of infrared light by each sample is not consistent, it is often taken based on experience. Generally, most of the absorption peaks in the spectrum chart not available are in the range of 10% to 80% transmittance. If the transmittance of the strongest absorption peak is too large (for example, greater than 30%), it means that the sampling amount is too small; on the contrary, if the strongest absorption peak is near the light transmittance of 0% and it is a flat peak, it indicates the sampling amount Too much, you should adjust the sample size and re-measure.

7. The sample for measurement should be dried, otherwise, it should be dried for several minutes under the infrared lamp after grinding. After the sample is ground and installed in the mold, it should be connected to a vacuum pump and evacuated for at least 2 minutes, so that the moisture in the sample is further removed, and then pressurized to 0.8 1GPa (8 10T / cm2). ) After 2 to 5 minutes. Not vacuuming will affect the transparency of the film.

8. The amount of KBr taken during tableting is generally about 200mg (also based on experience). The amount of KBr should be controlled according to the thickness of the tablet after the tablet is made. Generally, the thickness of the tablet should be less than 0.5mm. When the thickness is greater than 0.5mm, it is often possible Interference fringes were observed on the spectrum, which interfered with the spectrum of the test sample.

9. When pressing the tablet, you should first take the test sample and then add KBr to study it again, so that it is easier to mix. The agate mortar should be used for grinding. Because the inner surface of the glass mortar is rough, it is easy to adhere to the sample. When grinding, force should be applied uniformly in the same direction (clockwise or counterclockwise). If the grinding is not performed in the same direction, the test sample may be crystallized during the grinding process, which will affect the measurement results. The grinding intensity does not need to be too large, and the small particles that can be seen by the naked eye can no longer be ground. After the sample has been ground, it should be poured into a tabletting mold through a small funnel (it is difficult to pour directly because the mold mouth is small), and the sample is spread as evenly as possible, otherwise there are few samples after tableting The transparency is lower than in the place with more samples, and therefore it has an influence on the measurement. In addition, if opaque white spots appear on the pressed tablets, it means that there are small particles in the ground samples that have not been ground, and the tablets should be re-pressed.

10. After pressing the mold for tableting, wipe off all parts immediately. If necessary, clean and dry with water. Store in a desiccator to avoid rust.