The single channel chloride ion water quality sensor is based on electrochemical or optical principles, and measures the concentration by measuring the changes in electrical or optical signals generated by the interaction with chloride ions. The measurement methods can be classified into the following two categories, and need to be combined with calibration, operating procedures, and data analysis to ensure accurate results:
1、 Electrochemical measurement method
electrode method
Principle: The sensor has built-in sensing electrodes (such as silver/silver chloride electrodes) and reference electrodes. Chloride ions undergo redox reactions with the surface material of the electrodes (such as silver ions), resulting in a potential difference or current change. The potential difference or current magnitude is linearly related to the concentration of chloride ions, and the concentration can be calculated by measuring changes in electrical signals.
Operation steps:
Calibration: Use standard chloride ion solutions (such as 10mg/L, 100mg/L) to perform two-point calibration on the sensor to ensure accurate correspondence between electrical signals and concentrations.
Measurement: Immerse the sensor into the water sample to be tested and record the reading after the electrical signal stabilizes.
Cleaning: After the measurement is completed, rinse the electrode with deionized water to avoid residue interference with subsequent measurements.
Features: Fast response time (usually<1 minute), good stability, suitable for large-scale water sample monitoring (such as water plants, sewage treatment plants).
membrane method
Principle: The sensor surface is covered with a selectively permeable membrane, and chloride ions interact with the internal electrolyte through the membrane, changing the charge distribution or conductivity of the membrane, and then measuring the concentration through changes in electrical signals.
Operation steps: Similar to the electrode method, but it is necessary to regularly check the integrity of the membrane to avoid measurement errors caused by damage.
Characteristics: Strong anti-interference ability, suitable for complex water quality (such as water samples containing organic matter or heavy metals).
2、 Optical measurement method
Spectrophotometry
Principle: Using chloride ions to react with specific reagents to generate colored compounds, the concentration is calculated by measuring the absorbance of the compound at a specific wavelength (such as 480nm) and combining it with a standard curve.
Operation steps:
Sampling: Collect the water sample to be tested and filter it to remove suspended solids.
Color development: Add a color developing agent (such as diphenylcarbazone) to react and generate colored compounds.
Measurement: Place the colored solution into a spectrophotometer, measure the absorbance, and check the concentration on the standard curve.
Features: High precision (error<5%), but complex operation and time-consuming (about 30 minutes), suitable for laboratory or high-precision monitoring scenarios.
fluorescence method
Principle: After chloride ions bind with fluorescent probes (such as lanthanide complexes), the fluorescence intensity or lifetime changes, and the concentration is determined by measuring the change in fluorescence signal.
Operation steps: Similar to spectrophotometry, but requires the use of a fluorescence spectrometer for measurement.
Features: High sensitivity (able to detect chloride ions as low as μ g/L), but high equipment cost, suitable for monitoring ultra-low concentration chloride ions (such as drinking water sources).
3、 Key precautions
Calibration and maintenance
Regularly calibrate sensors with standard solutions to ensure measurement accuracy.
Electrochemical sensors need to avoid electrode passivation (such as the formation of silver sulfide on the surface of silver electrodes), while optical sensors need to prevent reagent deterioration or optical path contamination.
Control of interference factors
Electrochemical method: To avoid the presence of interfering substances such as bromide ions and iodide ions in water samples, interference can be eliminated through pretreatment (such as adding masking agents).
Optical method: Control the pH value of the water sample (such as spectrophotometry, which requires reaction at pH 1-2) to avoid color or turbidity interference with absorbance measurement.
Data recording and analysis
Record measurement time, location, water sample temperature and other parameters for easy traceability of abnormal data.
Combining historical data to analyze the trend of chloride ion concentration changes, providing a basis for water quality management (such as determining whether sewage discharge exceeds the standard).