Summary of abnormal reasons for gas chromatography results
I. Abnormal peak shape
- Leading
Reasons: ① Column overload (too large injection volume); ② Improper carrier gas flow rate; ③ Column temperature is too low to cause sample condensation.
Solution: ① Reduce the injection volume or dilute the sample; ② Optimize the carrier gas flow rate; ③ Appropriately increase the column temperature.
2.Tailing
Reasons: ① Active sites (such as contaminated liner, chromatographic column); ② Injection port contamination; ③ Mismatched stationary phase polarity.
Solution: ① Replace the liner or cut the front end of the chromatographic column; ② Use a deactivated liner; ③ Select a chromatographic column with appropriate polarity.
3.Split Peaks
Reasons: ① Poor injection technique (such as uneven speed); ② Foreign matter in the liner; ③ Sample decomposition.
Solution: ① Check the cleanliness of the liner; ② Ensure uniform injection speed; ③ Reduce the injection port temperature to prevent decomposition.
4. Flat Top
Reasons: Detector saturation or excessive injection volume.
Solution: ① dilute the sample; ② reduce the injection volume; ③ check the detector range setting.
II. Abnormal retention time
1.Retention time advanced
Reason: ① column temperature is too high, ② carrier gas flow rate increases, ③ chromatographic column aging.
Solution: ① calibrate column temperature and carrier gas flow rate; ② check the aging of the chromatographic column and replace it if necessary.
2.Delayed retention time
Reason: ① column temperature is too low; ② carrier gas flow rate decreases; ③ chromatographic column contamination.
Solution: ① optimize the heating program; ② check whether the carrier gas pressure is stable; ③ age or clean the chromatographic column.
III. Abnormal peak area/height
1.Peak area is unstable
Reason: ① poor injection repeatability (manual/automatic injector failure); ② uneven sample.
Solution: ① check the sealing of the injector; ② ensure that the sample is fully mixed; ③ optimize the volatilization conditions.
2.Peak height is too low
Reason: ① low detector sensitivity (such as improper FID gas ratio); ② too large split ratio
Solution: ① Adjust detector parameters (such as hydrogen/air flow rate); ② Reduce the split ratio or increase the injection volume.
IV. Ghost peak or impurity peak
Reason: ① Sample residue; ② Aging of septum/liner; ③ Impure carrier gas; ④ Sample decomposition.
Solution: ① Extend cleaning time; ② Replace aged consumables; ③ Use high-purity carrier gas; ④ Reduce the injection port temperature.
V. Peak loss
Reason: ① Target decomposition (too high temperature); ② The split ratio is too large; ③ The detector is not started.
Solution: ① Reduce the injection port/column temperature; ② Adjust the split ratio; ③ Confirm the detector power supply and parameter settings.
VI. Comprehensive processing steps
1.Confirm the abnormal type: observe the peak shape, retention time, peak area changes and additional peaks.
2.Check the instrument parameters: whether the temperature, flow rate, and detector settings are consistent with the method.
3.Maintenance consumables: Replace liner, septum, O-ring; cut or age the chromatographic column.
4.Optimize conditions: adjust injection volume, split ratio, and temperature program.
5.Eliminate contamination: run a blank experiment and check the purity of the carrier gas and sample.
VII. Preventive measures
1.Regular maintenance: clean the detector (such as FID nozzle) and replace consumables (liner, septum).
2.Method verification: use standard products to calibrate the system to ensure that the column is compatible with the sample.
3.Standard operation: train injection technology; avoid sample decomposition (such as derivatization treatment).
VIII. Special precautions
Carrier gas leakage: regularly check the tightness of the gas line to prevent pressure fluctuations.
Solvent effect: match the polarity of the solvent and the column, and optimize the injection port temperature.
Column installation: ensure that the column head is cut flat to avoid leakage or dead volume.
Most gas chromatography abnormalities can be effectively solved through systematic troubleshooting and targeted adjustments. Recording experimental details (such as consumable replacement and parameter adjustment) helps to quickly locate the root cause of the fault.
