GC Chromatogram Analysis

1. Read the chromatogram

A chromatogram plots detector response against time after injection. Retention time (tR) describes where a peak appears under a particular method; area is integrated detector response relative to a chosen baseline.

2. Use standards for identification

Compare retention times of candidate compounds with authentic standards under the SAME column, flow, temperature, and method. Coelution and method-dependent shifts make retention alone insufficient for unique identity.

3. Calculate uncorrected peak-area percentages

Suppose peak A has integrated area 420 and peak B has 580. Area% A = 420/(420+580) × 100 = 42.0%. This means 42% of the included integrated detector area, not automatically 42% of molecules, mass, purity, or yield.

4. Understand detector response

Detectors such as a thermal conductivity detector (TCD) can respond differently to different analytes. Calibrated concentrations require appropriate standards, response factors, integration and baseline checks, and consideration of unidentified or excluded peaks.

5. Validate chromatographic data

Confirm baseline placement, peak integration, potential overlapping peaks, injection reproducibility, detector operation, and replicate consistency before reporting quantitative differences.

Common interpretation mistakes

• Equating uncorrected area % to mol % or mass %.
• Assigning unknown identities by retention time alone.
• Mistaking retention-time separation for chromatographic resolution without considering widths.