GC Sampling System – Fundamentals

In process gas chromatography, more than 70% of analyzer problems originate from the sampling system. A well-designed sampling system ensures that a representative, clean, and stable sample reaches the GC injection valve.

Typical GC Sampling System Flow

The sampling system extracts process gas, removes contaminants, controls pressure and flow, and delivers a conditioned sample to the GC.

Sampling Valve – Purge vs Inject Operation

The GC sampling valve operates in two modes. During PURGE, the sample continuously refreshes the loop and vents. During INJECT, the valve switches and the carrier gas pushes the loop contents into the column.

Common Sampling System Failure Points

Sampling issues often cause slow response, drifting readings, missing peaks, or unstable chromatograms.

Key Points for Technicians

• Sampling system design is more critical than GC hardware.
• Most GC faults are caused by contamination or pressure instability.
• Always troubleshoot sampling before suspecting the analyzer.
• Stable pressure and flow ensure repeatable chromatography.