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Solving common problems in capillary analysis
First, the peak is lost
Possible causes and exclusions to be used:
1. The syringe is faulty and verified with a new syringe.
2. The detector is not connected, or the detector does not work, check the set value.
3. The injection temperature is too low, check the temperature and adjust as needed.
4. The oven temperature is too low, check the temperature and adjust as needed.
5. No carrier airflow, check the pressure regulator, check the leak, and verify the column feed rate.
6. Column breakage, if the column break is at the inlet end of the column or at the end of the detector, it can be remedied, cut off the broken part of the column and reinstall.
Second, the frontier peak
1. The column is overloaded to reduce the injection volume.
2. Co-elution of the two compounds increases sensitivity and reduces injection volume, reducing the temperature by 10 to 20 degrees to separate the peaks.
3. The sample is condensed, the inlet and column temperature are checked and the temperature is raised if necessary.
4. Sample decomposition, using a deactivated injector liner or lowering the injector temperature.
Third, trailing peak
1. The injector bushing or column adsorbs the active sample: replace the bushing. If the problem cannot be solved, remove the inlet end of the column for 1~2 turns and reinstall it.
2. The column or injector temperature is too low: warm up (do not exceed the maximum column temperature). The injector temperature should be 25 degrees above the highest boiling point of the sample.
3. Co-elution of two compounds: increase sensitivity, reduce injection volume, and reduce temperature by 10 to 20 degrees to separate peaks.
4. Column damage: Replace the column.
5. Column contamination: Remove 1~2 turns from the inlet end of the column and reinstall.
Fourth, only the solvent peak
1. There is something wrong with the syringe: verify with a new syringe.
2. Incorrect carrier gas flow rate (too low): Check the flow rate and adjust if necessary.
3. The sample is too dilute: inject a known sample to give good results. If the result is good, increase the sensitivity or increase the amount of injection.
4. The oven temperature is too high: check the temperature and adjust as needed.
5. The column cannot resolve the component from the solvent peak: replace the column with a thicker coating or a different polarity.
6. Carrier gas leak: Check the leak (with soapy water).
7. The sample is absorbed by the column or the injector bushing: the bushing is replaced. If the problem cannot be solved, remove 1~2 turns from the inlet end of the column and reinstall it.
Five, wide solvent peak
1. Due to improper column installation, a dead volume is created at the inlet: reinstall the column.
2. Poor injection technology (injection is too slow): Adopt fast and steady injection technology.
3. The injector temperature is too low: increase the injector temperature.
4. Sample solvent and detection interact (dichloromethane / ECD): Replace the sample solvent.
5. Residual sample solvent in the column: Replace the sample solvent.
6. Improper cleaning of the septum: adjustment or cleaning.
7. The split ratio is incorrect (the split flow rate is insufficient): Adjust the flow rate.
Six, false peak
1. The column adsorbs the sample, then desorbs: replace the liner. If the problem cannot be solved, remove 1~2 turns from the column inlet end and reinstall.
2. Syringe contamination: Try it with a new syringe and a clean solvent. If the false peak disappears, rinse the syringe several times.
3. The sample size is too large: reduce the injection volume.
4. Poor injection technology (injection is too slow: use fast and smooth injection technology.
7. Unidentified peaks appear in columns that have worked well in the past.
1. The column temperature is wrong: check and adjust the temperature.
2. Incorrect carrier gas flow rate: Check and adjust the flow rate.
3. The sample injection volume is too large: reduce the sample injection volume.
4. The injection technology level is too bad (injection is too slow): Adopt fast and steady injection technology.
5. Column and bushing contamination: Replace the bushing. If the problem cannot be solved, remove 1~2 turns from the inlet end of the column and reinstall it.
Eight, the baseline is irregular or unstable
1. Column loss or contamination: Replace the bushing. If the problem cannot be solved, remove 1~2 turns from the inlet end of the column and reinstall it.
2. Detector or injector contamination: Clean the detector and injector.
3. Carrier gas leakage: Replace the septum and check the column for leakage.
4. Uncoordinated carrier gas control: Check if the source pressure is sufficient. If the pressure is ≤ 500 psi, please replace the cylinder.
5. The carrier gas has impurities or gas path pollution: replace the gas cylinder and clean the metal tube with a carrier gas purification device.
6. The carrier gas flow rate is not within the maximum/minimum limits of the instrument (including hydrogen and air for FID): the flow rate is measured and verified according to the technical specifications of the manual.
7. The detector is out of order: check the instrument manual.
8. Injector septum drain: age or replace the septum.
Nine, the same column retention time varies
1. The column temperature is too low or too high to check and adjust the column temperature.
2. The carrier gas flow rate is too low or too high, and the flow rate is measured at the column outlet with an appropriate, calibrated gas source.
3. The sampler septum or column leaks, if necessary, check and repair.
4. The column is contaminated or damaged, re-aged or replaced.
5. Sample overload, reducing sample injection volume.
6. The recorder is out of order and the recorder is checked.
7. The carrier gas control is not coordinated. Check the carrier gas source to see if the pressure is sufficient. If the pressure is ≤ 500 psi, please replace the cylinder.