GC Timing vs Chromatogram – Core Concept

In process gas chromatography, valve timing directly controls what reaches the column and detector. Incorrect inject timing, cut window, or backflush sequence will immediately appear as missing, shifted, or distorted peaks on the chromatogram.

Valve Events and Chromatogram Relationship

This diagram overlays key GC events (inject, cut, backflush) with the resulting chromatogram peaks. Understanding this relationship is critical for troubleshooting repeatability and accuracy issues.

Key Points for Technicians

• Inject timing defines peak size and baseline stability.
• A narrow cut window causes missing or reduced peaks.
• A wide cut window causes overlapping and contamination.
• Early backflush removes heavy peaks prematurely.
• Late or missing backflush increases cycle time and fouls columns.

Typical Field Symptoms

• Peak shift → valve timing drift or clock mismatch
• Missing peak → inject or cut timing error
• Baseline rise → delayed or failed backflush
• Poor repeatability → unstable valve actuation