LNG (liquefied natural gas) chromatographic analyzer is widely used in the fields of energy and chemical engineering, and its stability directly affects the accuracy of analysis results. The following are common fault diagnosis and repair guidelines:
1、 Baseline drift or high noise
Fault phenomenon: The baseline is unstable and the noise level has significantly increased.
Diagnostic steps:
Check the gas system: Confirm that the purity of the carrier gas (such as high-purity nitrogen) meets the standard, and replace the filtering device or gas cylinder; Check if there is any air leakage at the connection of the gas path, and use a leak detector or electronic leak detector to investigate.
Column state: If non-volatile impurities are deposited at the inlet end of the chromatography column, the column needs to be aged at high temperature, but it must be 30 ℃ lower than the maximum operating temperature; If aging is ineffective, the front end can be cut 0.5-1 meters or the chromatographic column can be replaced.
Detector contamination: Clean the detector nozzle and collection electrode, treat with acetone ultrasonic treatment, and dry; Check if the detector circuit connection is loose.
Environmental interference: Ensure that the instrument is well grounded, away from mechanical vibration sources, and avoid power supply voltage fluctuations.
2、 Abnormal peak shape (tailing, splitting, changes in retention time)
Fault phenomenon: chromatographic peak asymmetry, splitting, or retention time shift.
Diagnostic steps:
Sample injection system issue: Check if the injection port liner is contaminated and replace the aging spacer; When using an automatic sampler, ensure that the plunger is not worn and installed correctly.
Column overload: Dilute the sample or reduce the injection volume to avoid overloading of the stationary phase.
Solvent effect: Choose an injection solvent that matches the polarity of the sample, or use a Retention Gap to improve sample focusing.
Improper split ratio: Adjust the split ratio to a reasonable range (recommended>20:1) to ensure that the sample is evenly introduced into the chromatographic column.
3、 Sensitivity reduction or signal loss
Fault phenomenon: Decreased peak area or no signal output.
Diagnostic steps:
Detector settings: Confirm that the detector parameters (such as the hydrogen/air ratio of FID and the bridge current of TCD) are set correctly to avoid exceeding the range.
Air path blockage: Check if the diversion trap is blocked and perform a diversion outlet test; Clean or replace the inlet filter.
Column loss: If the stationary phase is severely lost, the column needs to be replaced; Avoid high temperature overload when aging new columns.
Signal transmission failure: Check if the ion signal line is damp or has poor contact, and replace the line if necessary.
4、 Ignition failure (FID detector)
Fault phenomenon: The detector cannot ignite or the flame goes out.
Diagnostic steps:
Gas supply: Confirm that the hydrogen and air flow rates are set correctly, and check if the gas path valves are open.
Ignition system: Check if the ignition coil is open and observe if the ignition wire turns red; Clean the nozzle to prevent carbon buildup from affecting ignition.
Detector contamination: If the nozzle is blocked, clean it with acetone ultrasonic cleaning and dry it; Check if there is any air leakage inside the detector.
5、 Daily maintenance suggestions
Regular cleaning: Clean the injection port liner, splitter plate, and detector nozzle monthly, using acetone or ethanol ultrasonic treatment.
Gas leak detection: Use leak detection solution to check the sealing of each connection point every week to ensure no leakage.
Column protection: Connect a pre column or uncoated silica column before the chromatographic column to capture non-volatile impurities; Avoid prolonged high-temperature operation.
Consumables replacement: Regularly replace the injection pad, isolation pad, and gas filter, and use high-purity carrier gas (≥ 99.999%).