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The core of operating an infrared spectrometer is \"eliminating interference + capturing sample characteristics,\" with sample preparation and background correction being key steps. Through the aforementioned process, clear infrared spectra can be obtained, which are used for functional group identification, compound identification, and quantitative analysis (such as drug purity testing and material composition analysis). I. Working principle of infrared spectrometers: Infrared spectrometers analyze the chemical structure of substances by detecting their characteristic absorption of infrared light. The core principle behind this is the transition between molecular vibrational energy levels. The current mainstream instrument is the Fourier transform infrared spectrometer (FTIR), whose working process is as follows: 1. Light source emission: An infrared light source (such as a silicon carbide rod) generates infrared light with a wide wavelength range. 2. Interference spectroscopy: Infrared light enters a Michelson interferometer; the movement of the moving mirror creates a path difference, resulting in an interference light signal. 3. Sample function: The interference light passes through the sample, and light of specific wavelengths is absorbed by the vibrations of chemical bonds. 4. Signal detection: Detectors (such as thermocouples) convert the absorbed interference signal into an electrical signal. 5. Data processing: The computer performs a Fourier transform on the interference pattern to generate an infrared spectrum (with the abscissa representing wavenumber in cm⁻¹ and the ordinate representing absorbance). ✅Key point: The core advantages of FTIR are high resolution, a wide wavelength range (extending to the far-infrared region), and fast scanning speed. II. Operating procedure of the infrared spectrometer: Sample preparation → Instrument initialization → Background acquisition → Sample testing → Spectrum analysis. The core process involves background correction to eliminate environmental interferences and obtain the characteristic infrared absorption spectrum of the sample. Below are the detailed steps and precautions: 1. Preparation before operation (critical: sample preparation). The accuracy of infrared spectroscopy depends to 80% on sample preparation; it is necessary to choose an appropriate method based on the state of the sample: a. Solid samples (the compression method is most commonly used). Materials required: 1–2 mg of solid sample + 200 mg of dried KBr (optical grade, dried at 120°C for more than 4 hours to prevent moisture absorption). Steps: ① Place the sample together with KBr in an agate mortar (to avoid contamination) and grind it to a particle size of less than 200 mesh (to achieve a very fine powder and reduce light scattering) ； ② Fill the mixed powder into the tablet pressing mold and evacuate for 2 minutes (to remove trace moisture from the sample) ； ③ Apply pressure to 0.8–1 GPa (8–10 T/cm²) and maintain it for 2–5 minutes to produce transparent/semi-transparent thin films (with a thickness ≤ 0.5 mm, to prevent interference fringes in the spectrum). b. Liquid sample (liquid film method) material: polished NaCl/KBr crystal wafers (infrared transparent, non-reactive with liquids). Steps: Drop 1-2 drops of the liquid on one crystal sheet, then place another sheet on top to ensure that the sample forms a uniform thin film (samples with high viscosity can be applied directly onto a single crystal sheet). c. Surface/film samples (ATR method, Attenuated Total Reflection). Applicable scenarios: solid surfaces, viscous samples (such as rubber and coatings), or samples that are difficult to prepare. Steps: Install the ATR attachment (such as a ZnSe crystal with a refractive index of 2.4) in the instrument’s optical path, ensuring that the surface to be tested is in close contact with the crystal (to avoid any air gap); no grinding or dilution is required. 2. Instrument operation procedure (taking the Fourier transform infrared spectrometer as an example): Initialize the instrument by turning on the main unit and computer, and start the operation software (such as Thermo Fisher OMNIC, Bruker OPUS) ； Wait for the instrument’s self-check to complete (verify that the light source, interferometer, and detector are functioning properly). Purpose of collecting the background spectrum: to eliminate interference from CO₂ and moisture in the environment (these substances have strong absorption in the infrared region) ； Operation: Place a blank sample (such as an empty KBr sheet, a clean crystal sheet, or the “air background” of the ATR attachment) in the sample chamber, click the software’s “Background Acquisition” option, enter a name, and then start scanning. Background update: The background must be collected anew before each test (as CO₂ and humidity levels in the environment change), otherwise the spectrum will contain spurious peaks. After completing the background collection for sample testing, remove the blank sample and place the sample to be tested (solid slice, liquid film, or ATR sample) inside; then close the sample chamber lid ； Click \"Sample Collection\" in the software, enter the sample name, select the scanning range (usually 4000–400 cm⁻¹ to cover the mid-infrared region), and start the scan. After the spectrum processing and analysis scan is completed, the software automatically generates a \"Transmittance (T%) vs Wavenumber (cm⁻¹)\\" spectrum ； Spectrum processing: ① Baseline correction: Eliminating drift in the spectrum (such as spurious peaks in the background) ； ② Peak labeling: Identification of characteristic absorption peaks (such as -OH at 3200-3600 cm⁻¹, C=O at 1700-1750 cm⁻¹) ； ③ Spectrum library search: Identify the structure of compounds by comparing them with standard spectrum libraries (such as Sadtler). After completing the instrument shutdown test, remove the sample and clean the sample chamber (to prevent residual samples from corroding the optical components) ； Close the software, then turn off the host and the computer’s power supply in sequence ； When not in use for an extended period, turn the device on 1–2 times per week (for half a day each time), and also run the dehumidifier (to keep the laboratory humidity at ≤65% and prevent the equipment from getting damp). III. Key Points to Note 1. Sample preparation specifications for solid samples (compression method): The sample must not contain free water, as water will corrode the window slides and cause strong absorption at 1600–3600 cm⁻¹, resulting in distorted spectra ； Solid samples need to be dried under an infrared lamp for 5-10 minutes. Liquid sample (liquid film method): Control the thickness of the liquid film (too thick causes saturation of the strong absorption peak, while too thin results in a weak signal). Volatile/corrosive samples require a sealed liquid cell to prevent damage to optical components. Special samples: Samples containing metal powder or bubbles require preprocessing to avoid scattering interference ； For opaque solids, it is recommended to use the ATR attachment (Attenuated Total Reflection technique). 2. Instrument operation and environmental control: Temperature range of 15–30°C, humidity level of ≤65%; a stable power supply and a dehumidifier are required. Fourier-type instruments are sensitive to CO₂, so the laboratory needs to restrict personnel movement and ensure proper ventilation. Power-on procedure: Preheat for ≥30 minutes, and wait until the light source and detector are stable before conducting tests (to avoid baseline drift). Parameter settings: Resolution selection – 4 cm⁻¹ is recommended for routine organic compound analysis, while a value of over 8 cm⁻¹ is required for high precision. Number of scans: For low-concentration samples, this can be increased to 64 to improve the signal-to-noise ratio. 3. Maintenance and calibration: Routine maintenance – turn the device on at least 2 times per week, for half a day each time, to prevent the optical components from getting damp. After use, the AR crystal should be cleaned with ethanol/** to avoid scratches ； The liquid cell window is stored in a dry box. Key consumables: Detectors equipped with liquid nitrogen cooling require regular replenishment of liquid nitrogen (to maintain the safe liquid level). The tablet pressing die leaves KBr residues; apply rust preventive oil. Interference avoidance: Stay away from high-power devices; use a separate power supply for grounding. Safety note: Always wear protective gear when testing corrosive samples, and ensure that the sample chamber is sealed.