Lesson 19C.2

19C.2 HPLC and GC Quiz: Pearson Edexcel Chemistry, Unit 19

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 19C.2, HPLC and GC: 20 multiple choice questions for the Pearson Edexcel Chemistry (9CH0), Unit 19: Modern Analytical Techniques II, written with Revision Ninja.

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The 20 questions

  1. What determines the retention time of a component in HPLC?

    • Its interaction with the stationary phase relative to the mobile phase
    • The molar mass of the solvent used, which decides how fast each component is carried along
    • The colour of the component in the eluent, which determines how strongly it is detected
    • The laboratory temperature only, which is the sole factor controlling the retention time

  2. Which type of sample is best suited to gas chromatography?

    • Aqueous ions only, separated by charge
    • Solid polymers that cannot dissolve in any solvent
    • Non-volatile salts that melt above 1000 C
    • Volatile compounds that can be vaporised without decomposing

  3. Why is a mass spectrometer often used as the detector in forensic GC work?

    • It gives a mass spectrum for each peak, allowing identification of the compound
    • It only detects the presence of light-absorbing species, which is not a way of identifying compounds
    • It weighs each separated fraction on a balance, which gives the mass of each component
    • It measures the pH of each peak as it leaves the column, which identifies its acidity

  4. What is an advantage of HPLC over paper chromatography?

    • Its Rf values are always identical to a standard, which means every run gives the same spot position
    • It needs no solvent and works without any equipment, so it is cheap to run in any school laboratory
    • It separates gases only and cannot handle liquids, so it is limited to very volatile samples
    • It is faster and more sensitive, and it separates non-volatile or thermally unstable mixtures quantitatively

  5. In sports drug testing, why is GC combined with MS?

    • MS separates the components, and GC then identifies them by colour, which is read off the detector screen
    • GC makes the compounds more volatile so that MS can weigh them, which allows the mass of each to be found
    • MS removes the carrier gas so that GC can run faster, which reduces the time needed for the analysis
    • GC separates the mixture into components, and MS identifies each by its fragmentation pattern

  6. A GC peak has the same retention time as a standard run under identical conditions. What can be concluded?

    • The unknown must have a different molar mass from the standard, since its retention time is clearly different
    • The unknown may be the same compound, but further evidence such as mass spectrometry is needed
    • The unknown is an isomer that cannot be distinguished from the standard by any analytical method at all
    • The unknown is definitely the same compound, since retention time is unique to each substance under all conditions

  7. In gas chromatography, why is an inert carrier gas such as helium used?

    • It dissolves the sample so that it moves through the column as a liquid rather than a gas
    • It reacts with the stationary phase to create retention, so each component is held for a set time
    • It does not react with the sample or the column, so the components are not changed
    • It ionises the components so that they can be detected by the detector at the column outlet

  8. In HPLC, what is the mobile phase?

    • A sheet of paper that the solvent climbs by capillary action in a tank
    • A solid silica layer that remains stationary on a glass plate in the lab
    • A gas carried through a column of packing material by a pressure system
    • A liquid solvent pumped under high pressure through the column

  9. Which application is typical of HPLC?

    • Detecting the colour of metal salts in a flame
    • Measuring the melting temperature of pure solids
    • Analysis of drugs, amino acids and other non-volatile mixtures
    • Measuring the boiling temperature of volatile liquids

  10. Why is the column in HPLC packed with very fine particles?

    • It reduces the pressure needed to pump the solvent through the column
    • A large surface area gives more repeated partitioning, improving separation
    • It makes the solvent flow faster through the column, which shortens the time of each run
    • It removes colour from the sample before the components reach the detector

  11. A GC-MS peak has a molecular ion at m/z 46. Which compound is most likely?

    • Benzene, with Mr 78
    • Propanone, with Mr 58
    • Ethanol
    • Ethanoic acid, with Mr 60

  12. Which substance would be best analysed by GC rather than HPLC?

    • Hexane, a volatile hydrocarbon
    • A large protein that denatures on heating
    • A metal salt that decomposes above 200 C
    • A sugar polymer that is non-volatile

  13. Why are reference standards run alongside an unknown sample in a drugs test?

    • To remove water from the sample before injection, so that only dry compounds reach the column
    • To compare retention times, so unknown peaks can be matched to known compounds
    • To heat the column to a fixed temperature, which keeps the separation constant throughout the run
    • To confirm the carrier gas flow rate only, which is the sole purpose of running the standard

  14. An unknown compound has M+ at m/z 74 and a strong peak at m/z 31. Which compound fits?

    • Ethanoic acid, CH3COOH
    • Propanone, CH3COCH3
    • Benzene, C6H6
    • Butan-1-ol, C4H9OH

  15. Two GC peaks have retention times of 3.2 and 9.6 min. Which component is more volatile?

    • Both have equal volatility, since they come from the same sample
    • Neither, since retention times do not depend on volatility
    • The component with a 3.2 min retention time, since it is eluted sooner
    • The component with a 9.6 min retention time, since it is retained longer

  16. Why might HPLC be preferred for thermally unstable pharmaceuticals?

    • It removes the stationary phase, so no interaction occurs
    • It requires the sample to be a gas before injection
    • It separates at moderate temperatures, avoiding decomposition of the compounds
    • It heats the sample to very high temperatures to speed up separation

  17. Which evaluation of mass spectrometry alone for a mixture is best?

    • MS is unsuitable because it cannot measure molar mass at all, so it cannot identify any compound in a mixture
    • MS alone always identifies every component of any mixture unambiguously, without any separation step needed
    • MS alone may not distinguish isomers or resolve a mixture, so it is combined with a separation technique such as GC or HPLC
    • MS identifies components only by their colour in the ion beam, which makes separation unnecessary in practice

  18. In a GC trace, one peak has twice the area of another. What does this suggest?

    • Roughly twice the amount of that component, assuming a similar detector response
    • Twice the boiling temperature of that component, since larger peaks come from higher boiling compounds
    • Twice the retention time of that component, which means it stayed in the column for longer
    • Twice the molar mass of that component, since peak area depends directly on the molecular mass

  19. Which detector is commonly used in HPLC for compounds that absorb UV light?

    • A pH electrode placed at the column outlet
    • A flame ionisation detector for gases
    • A balance weighing each drop of eluent
    • A UV-visible absorbance detector

  20. In what unit is retention time usually reported in gas chromatography?

    • Degrees Celsius
    • Minutes
    • Millilitres of carrier gas
    • Percent of the sample

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