As the core equipment for detecting petroleum pollutants in water quality, the calibration quality of infrared spectrophotometer directly affects the accuracy and precision of monitoring data. The standardized debugging process should cover key links such as equipment preheating, parameter calibration, and system verification. The following provides a detailed explanation of the standardized operating system from a professional perspective.

1、 Confirmation of preparatory conditions

Before debugging, a basic environmental check must be completed: the laboratory temperature should be controlled at 25 ± 5 ℃, and the relative humidity should be ≤ 80% to avoid severe temperature and humidity fluctuations that may affect the stability of optical components. Check if the purity of the carbon tetrachloride extraction agent meets the premium purity standard. After soaking the glassware in chromic acid solution, perform ultrasonic cleaning to prevent cross contamination. After turning on the main power of the device, let it stand for 30 minutes to achieve thermal equilibrium of the light source system.

2、 Hardware system initialization

Start the control software to enter the calibration interface and perform the following operations in sequence:

1. Energy balance adjustment: Place a blank colorimetric dish in the sample cell, scan the full band absorbance, adjust the position of the reference filter to achieve a transmittance of over 95% for the characteristic absorption peak (such as the CH3 group at 3.4 μ m).

2. Slot width optimization: Select matching slot parameters based on the detection range, use narrow slots to improve resolution for high concentration samples, and switch to wide slots to enhance sensitivity for trace detection.

3. Detector gain calibration: Inject a standard oil sample of known concentration, dynamically adjust the voltage of the photomultiplier tube, and ensure that the signal strength is within the linear response range.

3、 Wavelength accuracy verification

Using polystyrene film standard material for wavelength correction: Place the standard film in the sample chamber, run a single beam scanning mode, and compare the deviation between the actual and theoretical values of the characteristic absorption peaks. If the wave number error exceeds ± 2cm ⁻¹, the software's automatic calibration function needs to be called to recalibrate the position of the interferometer's moving mirror. This step is crucial for ensuring the accuracy of subsequent quantitative analysis.

4、 Baseline correction and blank deduction

Take blank carbon tetrachloride solution purified by extraction as a reference and perform multi-point baseline calibration: collect background spectra in the range of 2800-3200nm and establish a smooth baseline equation. Pay special attention to eliminating the interference of stray light caused by solvent impurities, and if necessary, replace with fresh extractant to repeat the operation.

5、 Construction of standard curve

Prepare a series of gradient standard solutions (recommended 0.5-50mg/L) and extract and separate them according to the standard method of HJ637-2018. Inject samples sequentially to measure absorbance, remove outliers, and use the least squares method to fit the calibration curve. Focus on the linear correlation in the low concentration range, with a correlation coefficient R ² of ≥ 0.995. The detection limit of the synchronous verification method ensures compliance with the Class III standard for surface water.

6、 Performance verification experiment

Perform triple validation after completing calibration:

1. Precision testing: parallel measurement of the same standard sample 6 times, calculate the relative standard deviation RSD ≤ 3%;

2. Standard recovery test: Add different concentrations of standard solutions to actual water samples, and control the recovery rate at 90% -110%;

3. Interference experiment: Investigate the influence of common coexisting ions (such as S ² ⁻, CN ⁻) on the measurement results, and confirm that the anti-interference ability meets the standard requirements.

7、 Key points of daily maintenance

After daily work, blow the sample tank with dry nitrogen to prevent residual solvents from corroding optical components. Check the discoloration of the desiccant every month and replace the molecular sieve in a timely manner. Perform energy attenuation testing every quarter, and replace the infrared light source bulb when the reference signal is lower than 85% of the initial value.

By standardizing the debugging process, the measurement accuracy of the infrared spectrophotometer can be ensured to be stable within ± 5%, effectively supporting the smooth implementation of water quality monitoring work. In practical operation, it is necessary to strictly follow the instrument manual, monitor the process in conjunction with quality control samples, and promptly detect and eliminate system deviations.