Infrared spectrometer in daily maintenance precautions

Infrared spectrometer is an instrument that utilizes the absorption characteristics of infrared radiation of matter at different wavelengths to analyze molecular structure and chemical composition. Infrared spectrometers usually consist of light sources, monochromators, detectors, and computer processing information systems. According to different spectroscopic devices, it is divided into dispersion type and interference type. For the dispersive two-optical path optical zero balance infrared spectrophotometer, when the sample absorbs infrared radiation of a certain frequency, the vibrational energy level of the molecule transitions, and the light of the corresponding frequency in the transmitted light beam is weakened, resulting in a reference. The intensity of the corresponding radiation of the light path and the sample light path is poor, so that the infrared spectrum of the measured sample is obtained.

This article describes the maintenance considerations of the infrared spectrometer 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. 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.

3. If the test product is hydrochloride, due to ion exchange phenomena that may occur during the tableting process, the standard provides for the use of potassium chloride (also used after 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.

4. 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 every half a day for half a day while the dehumidifier is dehumidified. Especially in the mildew season, it is best to start the dehumidifier every day.

5, infrared spectroscopy determination of the most commonly used sample preparation method is potassium bromide (KBr) tablet method (Pharmacopoeia collection of more than 90% of this method used), so to reduce the impact of the determination, the use of KBr should preferably be optical For reagent grades, at least pure grades should also be analyzed. Before use, it shall be properly grounded (below 200 meshes), and dried at 120°C or above for more than 4 hours, then placed in a desiccator for use. 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%.

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 degree of infrared light absorption 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 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.

8. The amount of KBr taken when tableting is generally about 200mg (also based on experience), the amount of KBr should be controlled according to the thickness of the film after the tablet is produced. Generally, the thickness of the film should be less than 0.5mm, and when the thickness is more than 0.5mm, it can often be Interference fringes were observed on the spectrum and interfered with the spectrum of the test sample.

9. When pressing, you should first take the test product and then add KBr to re-grind it evenly. This is easier to mix. The grinding used should be an agate mortar, 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 sample 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 smaller 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 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.

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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