The common faults of continuous flow chemical analyzer (CFA) are concentrated in three categories: flow system blockage/leakage, abnormal detection signal, and abnormal temperature control/reaction. The core solution logic is to first locate the faulty module (flow path/detector/temperature control), and then gradually troubleshoot according to 'cleaning → inspection → replacement'. The following are specific faults and corresponding solutions:
1、 Flow system failures (most common, accounting for over 60%)
1. Flow path blockage (manifested as 0 flow rate, abnormal pressure increase, and large baseline fluctuations)
Common causes: particulate matter (such as precipitation and fibers) in the sample, reagent crystallization (such as phosphates and heavy metal salts), scaling on the inner wall of the pipeline, and valve/pump pipe blockage.
terms of settlement:
Preprocessing optimization: The sample needs to be filtered through a 0.45 μ m membrane to remove particulate matter; Easy crystallization reagents (such as ammonia nitrogen color reagents) can be prepared and used immediately, or anti crystallization agents (such as a small amount of ethanol) can be added.
Pipeline cleaning: Rinse the flow path with deionized water for 10-15 minutes. For stubborn blockages, soak in 5% -10% nitric acid (to remove metal scaling) or 1mol/L sodium hydroxide (to remove organic matter) for 30 minutes, and then thoroughly rinse with deionized water (to avoid residual acid and alkali corrosion of the pipeline).
Component inspection: Disassemble the injection valve, reaction coil, and detector flow cell, and clean residual impurities with a fine soft bristled brush (such as a nylon brush); If the inner wall of the pump tube is worn or adhered, replace it directly with a pump tube of the same specification.
2. Flow path leakage (manifested as residual liquid on the surface of the instrument, sudden drop in pressure, and trailing peaks)
Common causes: loose pipeline interfaces, aging and rupture of pump tubes, worn sealing rings (at the injection valve/flow cell), and inadequate sealing of the reaction cell.
terms of settlement:
Locate leakage point: After starting the instrument, observe the pipeline connections (such as joints, valves, and flow tanks), and focus on checking whether the sleeve between the pump pipe and the joint is loose.
Quick processing: Tighten loose joints (to avoid excessive force causing pipeline deformation); Replace the aging pump tubing (choose a material that matches the instrument, such as PTFE or silicone tubing); If the sealing ring is worn, replace it with a sealing ring of the same model (O-ring is commonly used for injection valves, and sealing gasket is used for flow tanks).
Preventive measures: Regularly check the aging condition of the pipeline (it is recommended to replace the pump tube every 3-6 months), and apply a small amount of vacuum grease to the joint (to enhance sealing and avoid adhesion).
2、 Detecting signal anomalies (directly affecting data accuracy)
1. Baseline drift/high noise (manifested as continuous baseline rise/fall, fluctuation amplitude exceeding the allowable range)
Common reasons: detector light source attenuation, circulation pool contamination, insufficient reagent purity (including impurities), low carrier gas purity (such as nitrogen containing moisture/oil), power interference.
terms of settlement:
Detector maintenance: Replace attenuated light source lamps (such as deuterium lamps, tungsten lamps, matched according to instrument models); Rinse the circulation tank with anhydrous ethanol or specialized cleaning solution to remove stains on the inner wall (if contamination is severe, ultrasonic cleaning can be performed for 5-10 minutes).
Reagent and carrier gas: Replace with high-quality pure reagents, filter and remove impurities before using the reagents; The carrier gas needs to be treated by a purification device (dehydration, de oiling) with a purity of ≥ 99.99%.
Environmental investigation: Ensure that the instrument is well grounded and kept away from high-power electronic devices (such as centrifuges and induction cookers) to avoid electromagnetic interference; The laboratory temperature remains stable (18-25 ℃) to reduce the impact of temperature fluctuations on the detector.
2. Abnormal peak shape (tailing, branching, poor reproducibility of peak height/peak area)
Common reasons: unstable injection volume, insufficient reaction conditions (insufficient temperature/reaction time), excessive dead volume in the pipeline, and high sample concentration (beyond the linear range).
terms of settlement:
Injection system inspection: calibrate the injection valve to ensure accurate injection volume; Clean the residual sample of the injection needle (rinse alternately with deionized water and reagent).
Optimization of reaction conditions: Adjust the reaction temperature (set according to the experimental method requirements, with an error of ≤± 1 ℃), extend the length of the reaction coil (increase the reaction time); If the sample concentration is too high, dilute it before injection (ensuring it is within the linear range of the detector).
Flow path optimization: reduce the length or curvature of the pipeline (avoid dead volume), replace the reaction coil with a suitable inner diameter (usually choose 0.5-1.0mm inner diameter, balance flow rate and reaction efficiency).
3. No signal output (manifested as no response from the detector and a straight peak shape)
Common reasons: The light source is not lit up, the detector is not connected (circuit failure), the flow cell is blocked (no sample passes through), and the reagent is not supplied properly (the pump tube is not pumping liquid).
terms of settlement:
Step by step investigation: First, check if the detector power is connected and if the light source is on (if not, replace the light source or check the circuit fuse); Observe if there is liquid flow in the flow path again. If the pump tube is not pumping liquid, check if the pump is working properly (such as if the motor is running); Finally, check if the circulation pool is blocked and handle it according to the "flow path blockage" method.
Circuit inspection: If the above troubleshooting is normal but there is still no signal, contact after-sales maintenance for the detector circuit (avoid disassembling it by yourself).
3、 Temperature control and abnormal reaction (affecting reaction completeness)
1. The reaction temperature cannot reach the set value/the temperature fluctuates greatly
Common causes: heating module failure (such as heating wire breakage), temperature sensor malfunction, temperature controller parameter drift, and rapid heat dissipation in the reaction tank.
terms of settlement:
Calibration and Inspection: Use a standard thermometer to calibrate the temperature control system of the instrument and reset the temperature control parameters; If the sensor fails, replace it with a temperature sensor of the same model (such as PT100 sensor).
Hardware maintenance: repair the heating module and replace the broken heating wire; Wrap the outer layer of the reaction tank with insulation cotton to reduce heat loss; Ensure good ventilation of the instrument to avoid triggering the overheating protection of the heating module.
2. Incomplete reaction (manifested as small peak area and low recovery rate)
Common reasons: low reaction temperature, improper reagent ratio (such as insufficient color reagent), short reaction time, uneven mixing of sample and reagent.
terms of settlement:
Optimize reaction conditions: increase the reaction temperature (such as from 30 ℃ to 40 ℃) according to experimental methods, and extend the reaction time (achieved by adjusting the length of the reaction coil or reducing the flow rate); Check the reagent ratio to ensure that the color reagent/reaction reagent is sufficient (diluted or supplemented in proportion).
Mixed system inspection: Check if the mixing coil is blocked to ensure that the sample and reagent are fully mixed; If the mixing effect is poor, replace the spiral mixing coil (to enhance turbulent mixing).
core principle
If the fault involves circuit or detector core components (such as light source driver board, temperature control motherboard) or cannot locate leakage/blockage points, do not disassemble them by yourself. Instead, contact the manufacturer's after-sales service for professional repair to avoid secondary damage.