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Abstract : Fourier transform infrared spectrometer is called the third generation infrared spectrometer. It uses the Michelson interferometer to interfere with the two-color infrared light whose optical path length changes at a certain speed to form interference light, and then interacts with the sample. The detector sends the interference signal to the computer for mathematical manipulations of the Fourier transform to restore the interferogram to a spectrogram. This article describes the maintenance precautions for the use of infrared spectrometer instruments in daily use.
1, the laboratory temperature should be measured at 15 ~ 30 °C, relative humidity should be below 65%, the power supply used should be equipped with a voltage regulator and ground wire. Due to the need to strictly control the relative humidity in the room, the area of ​​the infrared laboratory should not be too large, and the necessary equipment and equipment can be placed. However, indoor dehumidifiers must be provided.
2. In order to prevent the instrument from affecting the service life due to moisture, the infrared laboratory should always keep dry. Even if the instrument is not used, it should be turned on at least twice a week for half a day, and the dehumidifier should be dehumidified at the same time. Especially in the mildew season, it is best to start the dehumidifier every day.
3. If a single-beam infrared spectrophotometer (most widely used at present) is used, the CO2 content in the laboratory should not be too high. Therefore, the number of people in the laboratory should be as small as possible. Also pay attention to proper ventilation.
4. The most commonly used sample preparation method for infrared spectroscopy is the potassium bromide (KBr) tablet method (more than 90% of the varieties in the Pharmacopoeia use this method). Therefore, in order to reduce the influence of the measurement, the KBr used should be optical. For reagent grades, at least pure grades should also be analyzed. Before use should be properly studied (200 points below), and more than 120 °C baking more than 4 hours after the dryer set aside. If agglomerates are found, they should be dried again. The prepared empty KBr sheet should be transparent. Compared with air, the light transmittance should be above 75%.
5. If the test product is hydrochloride, due to ion exchange phenomena that may occur during the tableting process, the standard requires potassium chloride (also used as pretreatment with potassium bromide) instead of potassium bromide for pressure. Tablets, but it is also possible to compare the spectra measured after potassium chloride tableting and potassium bromide tableting. If there is no difference between the two, potassium bromide can be used for tableting.
6. The amount of the test sample to be taken when the tableting method is used is generally 1 to 2 mg, and it is impossible to use the scale to add it after weighing. The absorption degree of infrared light of each sample is inconsistent, so it is often used empirically. Most of the absorption peaks that are not available in the general requirements range from 10% to 80% transmittance. If the transmittance of the strongest absorption peak is too large (eg, greater than 30%), then the sample size is too small; conversely, if the strongest absorption peak is close to the light transmittance of 0%, and is a flat peak, then the sample size Too much, at this time should adjust the sample size and re-measurement.
7. The amount of KBr taken when tableting is generally about 200mg (also based on experience), and the amount of KBr should be controlled according to the thickness of the tablet after the tablet is produced. Generally, the thickness of the tablet should be 0.5mm or less, and when the thickness is more than 0.5mm, it can be frequently used. Interference fringes were observed on the spectrum and interfered with the spectrum of the test sample.
8. When pressing, you should first take the test product and then add KBr to re-grind evenly. This is easier to mix. The agate mortar should be used for grinding, because the inner surface of the glass mortar is rough and easy to adhere to the sample. Grinding should be in the same direction (clockwise or counterclockwise) evenly, if not in the same direction grinding, there may be in the grinding process for the test sample to produce crystal, thus affecting the measurement results. Grinding force is not too large, and grinding to the specimen is no longer visible to the naked eye of small particles. After the sample is well developed, it should be poured into the tableting die through a small funnel (due to the small die mouth, it is difficult to directly pour in), and try to spread the sample evenly, otherwise the sample after the tableting is less The transparency is lower than that of the sample, and therefore has an effect on the measurement. In addition, if the opaque white spots appear on the pressed sheet, it indicates that there are small particles that have not been studied in the prepared sample and should be re-tableted.
9. The sample for measurement should be dry, otherwise it should be baked after drying for a few minutes under the infrared lamp. After the sample is properly prepared and installed in the mold, it should be connected to a vacuum pump and then vacuumed for at least 2 minutes so that the moisture in the sample can be further pumped away and then pressurized to 0.8 to 1 GPa (8 to 10 T/cm2). ) After 2 ~ 5min. No vacuum will affect the transparency of the film.
10. After pressing the tablet with the mold, the parts should be wiped clean, cleaned with water and dried when necessary, and stored in a desiccator to rust the rabbit.
1, the laboratory temperature should be measured at 15 ~ 30 °C, relative humidity should be below 65%, the power supply used should be equipped with a voltage regulator and ground wire. Due to the need to strictly control the relative humidity in the room, the area of ​​the infrared laboratory should not be too large, and the necessary equipment and equipment can be placed. However, indoor dehumidifiers must be provided.
2. In order to prevent the instrument from affecting the service life due to moisture, the infrared laboratory should always keep dry. Even if the instrument is not used, it should be turned on at least twice a week for half a day, and the dehumidifier should be dehumidified at the same time. Especially in the mildew season, it is best to start the dehumidifier every day.
3. If a single-beam infrared spectrophotometer (most widely used at present) is used, the CO2 content in the laboratory should not be too high. Therefore, the number of people in the laboratory should be as small as possible. Also pay attention to proper ventilation.
4. The most commonly used sample preparation method for infrared spectroscopy is the potassium bromide (KBr) tablet method (more than 90% of the varieties in the Pharmacopoeia use this method). Therefore, in order to reduce the influence of the measurement, the KBr used should be optical. For reagent grades, at least pure grades should also be analyzed. Before use should be properly studied (200 points below), and more than 120 °C baking more than 4 hours after the dryer set aside. If agglomerates are found, they should be dried again. The prepared empty KBr sheet should be transparent. Compared with air, the light transmittance should be above 75%.
5. If the test product is hydrochloride, due to ion exchange phenomena that may occur during the tableting process, the standard requires potassium chloride (also used as pretreatment with potassium bromide) instead of potassium bromide for pressure. Tablets, but it is also possible to compare the spectra measured after potassium chloride tableting and potassium bromide tableting. If there is no difference between the two, potassium bromide can be used for tableting.
6. The amount of the test sample to be taken when the tableting method is used is generally 1 to 2 mg, and it is impossible to use the scale to add it after weighing. The absorption degree of infrared light of each sample is inconsistent, so it is often used empirically. Most of the absorption peaks that are not available in the general requirements range from 10% to 80% transmittance. If the transmittance of the strongest absorption peak is too large (eg, greater than 30%), then the sample size is too small; conversely, if the strongest absorption peak is close to the light transmittance of 0%, and is a flat peak, then the sample size Too much, at this time should adjust the sample size and re-measurement.
7. The amount of KBr taken when tableting is generally about 200mg (also based on experience), and the amount of KBr should be controlled according to the thickness of the tablet after the tablet is produced. Generally, the thickness of the tablet should be 0.5mm or less, and when the thickness is more than 0.5mm, it can be frequently used. Interference fringes were observed on the spectrum and interfered with the spectrum of the test sample.
8. When pressing, you should first take the test product and then add KBr to re-grind evenly. This is easier to mix. The agate mortar should be used for grinding, because the inner surface of the glass mortar is rough and easy to adhere to the sample. Grinding should be in the same direction (clockwise or counterclockwise) evenly, if not in the same direction grinding, there may be in the grinding process for the test sample to produce crystal, thus affecting the measurement results. Grinding force is not too large, and grinding to the specimen is no longer visible to the naked eye of small particles. After the sample is well developed, it should be poured into the tableting die through a small funnel (due to the small die mouth, it is difficult to directly pour in), and try to spread the sample evenly, otherwise the sample after the tableting is less The transparency is lower than that of the sample, and therefore has an effect on the measurement. In addition, if the opaque white spots appear on the pressed sheet, it indicates that there are small particles that have not been studied in the prepared sample and should be re-tableted.
9. The sample for measurement should be dry, otherwise it should be baked after drying for a few minutes under the infrared lamp. After the sample is properly prepared and installed in the mold, it should be connected to a vacuum pump and then vacuumed for at least 2 minutes so that the moisture in the sample can be further pumped away and then pressurized to 0.8 to 1 GPa (8 to 10 T/cm2). ) After 2 ~ 5min. No vacuum will affect the transparency of the film.
10. After pressing the tablet with the mold, the parts should be wiped clean, cleaned with water and dried when necessary, and stored in a desiccator to rust the rabbit.
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