As the core detection equipment for petroleum pollutants in water quality, the operation standardization of infrared spectrophotometer directly affects the accuracy of data and experimental efficiency. The following is a detailed breakdown of the standardized usage process:
1、 Pre preparation and sample preparation
1. Instrument status check
-Confirm that the power connection is normal, turn on the host and computer control system, and start the supporting software to perform a self-test program.
-Check whether the silicon wafer (or glass) colorimetric dish is clean and free of scratches. If necessary, wipe it with ethanol and dry it for later use.
2. Sample collection and preservation
-When collecting water samples, avoid surface floating oil and use brown glass bottles to contain them. Add hydrochloric acid to acidify to pH ≤ 2 to inhibit microbial degradation of oil.
-If the water sample contains suspended solids, it needs to be filtered through a glass fiber filter membrane; Complex matrices can be enriched by liquid-liquid extraction using carbon tetrachloride.
2、 Instrument initialization and calibration
1. Baseline correction (blank measurement)
-Inject blank extractant (such as n-hexane) into the colorimetric dish, place it in the sample cell, and close the compartment door.
-Activate the 'baseline calibration' function, and the instrument will automatically scan the entire frequency band and record the background absorption spectrum to eliminate solvent and environmental interference.
2. Drawing of standard curves
-Configure a standard oil solution with gradient concentration (such as 0.5-8 mg/L) and measure the absorbance sequentially.
-Select the characteristic absorption peak (usually the methyl/methylene vibration peak near 2930 cm ⁻¹), generate a standard curve through multi-point fitting, and the correlation coefficient R ² should be ≥ 0.995.
3、 Sample measurement and quality control
1. Sample testing
-Transfer the processed sample extract to a colorimetric dish to avoid the formation of bubbles, quickly seal it, and place it in the sample compartment.
-Click on 'Sample Measurement', the instrument automatically completes spectral scanning and compares it with the standard curve, outputting instantaneous concentration values.
2. Parallel sample and spiked recovery
-At least two parallel samples should be taken from each batch of samples, and the relative deviation should be controlled within ± 5%.
-Randomly select 10% of the samples for spiked recovery testing to verify the accuracy of the method (recovery rate should be between 90% and 110%).
4、 Data processing and result judgment
1. Data correction
-Convert the original concentration based on the dilution factor of the sample, deduct the blank value and salinity correction factor (if any).
-Abnormal high values require re sampling and re examination to eliminate interference from emulsifiers, surfactants, etc.
2. Report generation
-The system automatically generates a detection report, including sampling information, spectrum overlay comparison, and over limit warning.
-Laboratories that meet the requirements of HJ 637-2018 standard can directly issue legally binding data.
5、 Shutdown maintenance and precautions
1. Daily maintenance
-After the measurement is completed, rinse the colorimetric dish with anhydrous ethanol and blow dry with nitrogen to prevent cross contamination.
-Regularly clean the dust accumulated in the light source and check if the discolored silicone gel inside the drying tube has failed.
2. Safety Tips
-Discarded extraction solution should be disposed of as hazardous waste, and it is strictly prohibited to directly pour it into the sewer.
-Avoid running the instrument without load for a long time and extend the service life of the deuterium lamp.
This process strictly follows the logical chain of "pre-processing calibration measurement quality control reporting", and through standardized operations, it can effectively avoid errors caused by environmental temperature and humidity fluctuations, insufficient reagent purity, and other factors, ensuring that the test results meet the requirements of the GB/T series standards. In practical operation, it is necessary to adjust the parameter settings based on the specific instrument model. It is recommended to submit for measurement certification every year to ensure the traceability of measurement values.