1、 Reagent replacement: the core link to ensure measurement accuracy
Reagent shelf life management
The reagents used in the total nitrogen analyzer, such as potassium persulfate and sodium hydroxide, have a shelf life of one month at low temperatures (4-10 ℃) and only seven days at room temperature. Expired reagents can lead to a decrease in oxidation efficiency, low measurement values, and even blockage of digestion pipelines. For example, a certain sewage treatment plant caused a total nitrogen measurement error of 30% due to failure to replace reagents in a timely manner, which was investigated as a result of reagent failure.
Replace the operating specifications
Protective measures: Wear corrosion-resistant gloves (such as nitrile material) and goggles to avoid contact of reagents with the skin.
Operation steps:
Turn off the instrument power and discharge residual reagents;
Dismantle the old reagent bottle, rinse the bottle mouth and connecting pipeline with pure water three times;
Inject new reagent (shake well) to ensure that the liquid level is above the scale line;
Start the instrument, run the 'reagent initialization' program, and eliminate any bubbles in the pipeline.
Taboo: It is strictly prohibited to pour new reagents directly into old bottles to prevent cross contamination; The standard solution needs to be stored in a refrigerated and sealed container, and restored to room temperature before use.
Verification and recording
After replacement, a standard solution (such as potassium hydrogen phthalate with a concentration of 50mg/L) should be used for verification, and measurements should be taken continuously for 3 times with an error of ≤± 5%. Record the replacement date, reagent batch number, and verification results, and establish a reagent management ledger.
2、 Pipeline cleaning: key to preventing blockage and cross contamination
Cleaning cycle and scenario
Daily cleaning: After daily analysis, rinse the injection tube with pure water for 10 minutes to remove residual samples.
Deep cleaning: Clean the pipeline with a 10% hydrochloric acid solution for 30 minutes per week to dissolve inorganic salt deposits; Clean organic pollution with isopropanol every month.
Special scenario: After replacing reagents or measuring high concentration samples (such as total nitrogen>100mg/L), immediate cleaning is required.
Key points of cleaning operation
Injection system: Disassemble the injection needle and clean it with an ultrasonic cleaner (frequency 40kHz) for 15 minutes to remove any blockages at the needle tip.
Digestion module: Rinse the digestion tank with pure water until there are no bubbles to prevent residual reagents from corroding the glass.
Discharge system: Check if the peristaltic pump tube is aging and replace it every 3 months to prevent leakage and corrosion of the circuit board.
effect verification
After cleaning, run the 'blank test'. If the total nitrogen measurement value is ≤ 0.5mg/L, the cleaning is qualified; Otherwise, repeated cleaning or inspection of pipeline sealing is required.
3、 Optical path calibration: the core maintenance to ensure the accuracy of optical detection
Calibration cycle and conditions
Regular calibration: Perform optical path calibration once every quarter, or trigger calibration when the measured value fluctuates by more than 10%.
Environmental requirements: Before calibration, it is necessary to stabilize the ambient temperature (20 ± 5 ℃) and humidity (<70%), and avoid direct sunlight on the instrument.
Calibration operation process
Zero point calibration: Inject pure water into the optical colorimetric dish, run the "zero point calibration" program, and adjust the baseline to 0 ± 0.1mV.
Span calibration: Inject standard solution (such as potassium nitrate, concentration 10mg/L), adjust the gain to make the output signal 1000 ± 50mV.
Wavelength verification: Use a mercury lamp (wavelength 253.7nm) to check the wavelength accuracy of the monochromator, with an error of ≤± 1nm.
Common problem handling
Signal drift: Check the lifespan of the light source (such as deuterium lamp), and replace it if the usage time exceeds 2000 hours.
Lens contamination: Dip a dust-free cloth in pure alcohol and gently wipe the lens to avoid scratches; If the pollution is severe, contact the manufacturer for replacement.
Data exception: Run the "Optical Path Self Check" program to check if the voltage of the photoelectric converter (PMT) is stable (usually -800V ± 50V).
4、 Maintenance records and fault prevention
Establish and maintain archives
Record the date, content, consumables replaced, and calibration parameters of each maintenance to create a traceable maintenance log. For example, a certain enterprise found a positive correlation between the frequency of reagent replacement and measurement error through analysis and maintenance records. After optimization, the error was reduced from ± 8% to ± 3%.
Preventive maintenance recommendations
Consumables management: Reserve vulnerable parts such as filter cartridges and sealing rings according to usage frequency to avoid downtime caused by missing parts.
Personnel training: Regularly provide maintenance skills training to operators to ensure they master key operations such as reagent replacement and pipeline cleaning.
Remote monitoring: Configure IoT modules to monitor instrument status in real-time and provide early warning of potential faults.
Conclusion
The reagent replacement, pipeline cleaning, and optical path calibration of the total nitrogen online analyzer are the three core maintenance steps to ensure measurement accuracy. By strictly following operating procedures, establishing maintenance records, and implementing preventive maintenance, the instrument failure rate can be significantly reduced (such as reducing pipeline blockage rate from 15% to 3%), and the service life can be extended (averaging 2-3 years), providing reliable data support for water quality monitoring.