ALLPCB
Gas chromatographs have complex structures, many adjustable conditions, and long recovery times. Various faults can occur during use, and failure to address root causes can lead to serious consequences. This article summarizes common faults encountered in applications and practical troubleshooting steps.
1. No chromatographic peaks after injection
If the detector output remains a straight line and the detected signal does not change after injection, inspect components in order from the syringe and inlet toward the detector.
- Check whether the syringe is blocked. If the syringe is OK,
- check that the inlet and detector graphite seals or ferrules are tight and not leaking,
- inspect the column for fractures or leaks,
- finally, verify that the detector outlet is unobstructed.
The detector outlet being clear is especially important. A common scenario is: the instrument worked fine one day but produced no peaks the next. After confirming the inlet, syringe, seals, and column were normal, it was found that the inlet head pressure could not reach the setpoint and remained high. This pointed to a blocked ECD outlet. Because ECD effluent includes some radioactive material, the ECD outlet is vented outdoors. In this case, rainwater had entered the ECD exhaust and frozen, blocking the outlet. The blocked outlet prevented gas flow through the system, so no sample reached the detector and no peaks appeared.
2. Baseline problems
Baseline noise, drift, or wandering increase measurement error and can render the instrument unusable. When a baseline problem occurs, first check whether instrument conditions have changed or whether gas cylinders or accessories were recently replaced.
If conditions or supplies were changed, determine whether those changes caused the baseline issue. For example, insufficient carrier gas purity can cause a gradual baseline rise after switching cylinders, because gas purifiers may not show an immediate effect. In one case, switching to a new carrier gas led to a higher baseline and severe baseline noise the next day, burying all peaks. Replacing the carrier gas resolved the problem immediately.
After ruling out supply or condition changes, inspect the following:
- worn inlet septa or seals; establish a schedule to replace inlet septa regularly,
- quartz wool that may need replacement,
- cleanliness of liner inserts. When cleaning a liner, soak it in the final solvent used to prepare the sample, sonicate for a few minutes, then heat in a furnace to a temperature slightly above operating temperature before reinstalling.
Detector contamination can also cause baseline problems; cleaning or thermal cleaning of the detector may resolve such issues.
3. Missing peaks
Peaks can be lost for two main reasons: contamination in the gas path or insufficient chromatographic separation.
3.1 Contamination in the gas path
This type of peak loss can often be resolved by multiple blank runs and by cleaning the gas path, including the inlet and detector. To reduce contamination:
- include a high-temperature bake or cleaning step at the end of temperature programs,
- ensure injected samples are clean,
- minimize use of high-boiling oils,
- use the highest practical inlet, column, and detector temperatures.
3.2 Insufficient separation or column degradation
If peaks are not separated, in addition to contamination, reduced column efficiency from system contamination or column aging may be the cause. Column aging typically leads to gradual loss of peaks over time.
Ghost peaks usually result from system contamination or leaks; their resolution also involves leak checking and removal of contaminants. In routine operation, record the baseline under normal conditions to provide a reference during maintenance.
The methods described here cover three common troubleshooting scenarios. Gas chromatographs have many potential failure points and restoration can take time. Effective maintenance depends on correct root-cause analysis. Compare results step by step as you inspect each component, avoid amplifying the problem, and with systematic checks and repetitions you can resolve most issues.
