Analytical instrumentation application: Gas chromatography (GC) is primarily used to measure which quantity in a sample stream under appropriate calibration and detection?

Introduction / Context:
Gas chromatography separates volatile components based on differential partitioning between stationary and mobile phases. After separation, detectors quantify each component, enabling compositional analysis essential to process control, quality assurance, and emissions monitoring.

Given Data / Assumptions:

• GC system with appropriate column and detector (e.g., FID, TCD).
• Calibration curves relate detector response to amount.
• Sample properly conditioned for volatility and stability.

Concept / Approach:
GC produces chromatographic peaks whose areas (or heights, with caution) are proportional to moles or mass of each component injected. With calibration, peak areas convert to concentration or mole fraction in the original stream. Temperature and pressure are controlled system variables, not the measurand. Flow rate is a carrier-gas or process parameter that influences retention but is not what the GC reports as the analytical result.

Step-by-Step Solution:

Verification / Alternative check:
Typical GC outputs list peak areas and calculated wt%/mol%/ppm for each analyte following calibration standards.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing detector signal with absolute mass without calibration; quantitation requires standards and response factors.

Final Answer:
Concentration