A sports scientist collects a urine sample from an athlete and sends it to a laboratory for analysis. The laboratory uses gas chromatography (GC) linked to mass spectrometry (MS) to test whether the sample contains any banned performance-enhancing substances. Explain how GC-MS allows the laboratory to identify any banned substances present in the urine sample.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Gas chromatography separates the mixture into its individual components.
The different components travel through the GC column at different speeds, so they reach the detector at different times.
Each separated component then enters the mass spectrometer.
The mass spectrometer produces a fragmentation pattern (mass spectrum) for each component.
The mass spectrum is compared to a database or library of known substances to identify the component.
The different components travel through the GC column at different speeds, so they reach the detector at different times.
Each separated component then enters the mass spectrometer.
The mass spectrometer produces a fragmentation pattern (mass spectrum) for each component.
The mass spectrum is compared to a database or library of known substances to identify the component.
Examiner tips
- Use the word "separates" for GC, "different speeds" for retention time, "fragmentation pattern" for MS, and "compare to a database" for identification.
- Include all five points in the correct order to match the mark scheme.
- Use UK spelling (e.g., "identification").
Common mistakes
- Confusing the order of GC and MS steps, or saying the GC gives a mass spectrum.
- Failing to mention the comparison to a database or library for identification.
Mark scheme (5 marks)
- Gas chromatography separates the mixture into its individual components
- Different components travel through the GC column at different speeds / take different amounts of time to pass through
- Each separated component then enters the mass spectrometer
- The mass spectrometer produces a fragmentation pattern / mass spectrum for each component
- The mass spectrum is compared to a database / library of known substances to identify the component
Key terms in this question
gas chromatography · mass spectrometry
Related
- All Edexcel A-Level Chemistry (9CH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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