1、 Comparison of operating procedures
Titration colorimetric method
Reagent preparation: It is necessary to prepare hydrochloric acid standard solution, phenolphthalein/methyl orange indicator, and regularly calibrate the reagent concentration (such as 0.1mol/L hydrochloric acid, which needs to be calibrated every 3 months).
Water sample treatment: It is necessary to filter and remove suspended solids (particle size>0.45 μ m) to avoid turbidity and interference with colorimetry; High salinity water samples need to be pre diluted (such as diluting 10 times for seawater alkalinity detection).
Titration operation:
Phenolphthalein alkalinity: Take 100mL of water sample, add 4 drops of phenolphthalein, titrate with hydrochloric acid until colorless, and record the volume V1.
Total alkalinity: Add 3 drops of methyl orange and continue titration until it turns orange red. Record the volume V2.
Result calculation: Total alkalinity (mg/L)=(V1+V2) × C × 50.04/V water sample (C is the concentration of hydrochloric acid).
Operation time: Approximately 15 minutes per test (including reagent addition, titration, and recording).
Electrochemical method (taking electrode method as an example)
Electrode calibration: Use standard buffer solutions (pH 4.01, 7.00, 10.01) for three-point calibration, with each calibration taking 5 minutes.
Water sample collection: No pre-treatment is required (but it is necessary to avoid bubbles adhering to the electrode), and the sample is directly taken to the detection tank.
Real time monitoring: The electrode continuously contacts the water sample and automatically calculates the alkalinity through potential changes (such as pH electrode combined with ion selective electrode).
Data output: The measurement value is updated every 5 seconds and supports 4-20mA signal output to the PLC.
Operation time: 20 minutes for the first calibration, and real-time output for subsequent monitoring.
2、 Selection suggestions
Prioritize the scenario of titration colorimetric method
High precision requirements: For monitoring the total alkalinity of drinking water plants (national standard requirement ≤ 1mmol/L), it must comply with the GB 5749-2022 standard.
Low frequency testing: ≤ 4 tests per day, and the operator has chemical analysis qualifications (such as laboratory environment).
Limited budget: The equipment procurement cost is low (about RMB 20000), but it requires a higher consumption of reagents.
Case: The circulating cooling water system of a certain steel plant adopts MZD-JDS-2012 titrator, which achieves one detection per hour through an automated sampling device, with an error controlled within ± 1.5%.
Prioritize the scenario of electrochemical method
Real time monitoring requirements: such as alkalinity control of aeration tanks in sewage treatment plants (requiring adjustment of dosage every 5 minutes).
Adverse environment: high salinity (such as seawater desalination pretreatment), high turbidity (such as papermaking wastewater) scenarios, electrode method has stronger anti-interference ability.
Long term operation: 24-hour continuous monitoring is required, and maintenance personnel have basic electrical skills (such as electrode replacement).
Case: A wastewater treatment plant in a chemical industrial park uses an EZ alkalinity hardness analyzer to achieve remote alarm through an IoT platform, reducing manual inspection frequency by 70%.
3、 Trends and upgrade directions
Titration colorimetric method: Upgrade to "microinjection+automation", such as using a micro injection pump instead of manual titration, reducing single reagent consumption from 2mL to 0.1mL.
Electrochemical method: Combining AI algorithms to compensate for electrode drift, such as predicting electrode life through machine learning models and triggering maintenance reminders in advance.
Fusion solution: Deploy electrochemical real-time monitoring at key nodes (such as water outlets), and configure titration colorimetric method for regular verification in the laboratory to balance cost and accuracy.