Gas Chromatography–Mass Spectrometry (GC-MS)
Couples a gas chromatograph to a mass spectrometer so each volatile compound is separated and then identified from its fragmentation pattern. Used for unknown volatile impurities, nitrosamines, residual solvent confirmation and extractables.
- Pharmaceutical
- Environmental
- Forensic and toxicology
- Food & flavour
- Petrochemical
- Packaging
Test your GC-MS knowledge
Multiple-choice questions
Pick an answer to see whether you are right and why.
Q1. What electron energy is standard for EI mass spectra used in library searching?
basicQ2. Which compound is commonly used to autotune a GC-MS?
basicQ3. High m/z 28 and 32 in a GC-MS tune report indicate:
intermediateQ4. Why is SIM mode more sensitive than full scan?
intermediateQ5. Ions at m/z 207 and 281 rising at high oven temperature usually come from:
intermediateQ6. A library search gives a 92% match for an unknown peak. What should you conclude?
basic
Viva questions
Think of your answer first, then open it to compare.
1. What do you check in a GC-MS autotune report?
Mass assignment of m/z 69, 219 and 502, peak widths, relative abundances, isotope ratios (70/69, 220/219, 503/502), electron multiplier voltage, and air and water levels (m/z 18, 28, 32). Each must meet the manufacturer's or SOP criteria.
2. Why is a solvent delay set in GC-MS methods?
It keeps the filament off while the large solvent peak passes, protecting the filament and detector and preventing source contamination.
3. Why might GC-MS be chosen over LC-MS for an alkyl halide mutagenic impurity?
Alkyl halides are small, volatile and ionise poorly by electrospray. GC separates them well and EI ionises them reliably, and SIM or MRM gives the low limits that ICH M7 control requires.
Keep every GC-MS in control: usage logs, calibration and maintenance schedules, and automatic blocking of overdue instruments.