High-resolution mass spectrometry and chromatographyEdexcel International A Level Chemistry: Flashcards

What these 14 flashcards ask

What does a high-resolution mass spectrometer measure that a low-resolution one does not?
Why do compounds with the same nominal Mr have different accurate Mr?
State the accurate relative atomic masses of H, N and O used in calculations.
How do you use accurate Mr to suggest a formula?
Define the mobile phase in chromatography.
What is the stationary phase in paper chromatography and in TLC?
Give the formula for Rf.
Why is the start line drawn in pencil?
Why does a more polar compound have a lower Rf on silica with a non-polar solvent?
What is the mobile phase in gas chromatography?
What is the mobile phase in HPLC?
What is retention time?
Why is GC-MS more reliable than GC alone?
Give two uses of GC-MS or HPLC-MS.

Exam questions on High-resolution mass spectrometry and chromatography

Carbon monoxide, nitrogen and ethene all have the same nominal relative molecular mass of 28. A chemist uses a high-resolution mass spectrometer to analyse gases. Accurate relative atomic masses: H = 1.0078, C = 12.0000, N = 14.0031, O = 15.9949.
Calculate the accurate relative molecular mass of propanone, C₃H₆O, to four decimal places.2 marks
A student uses one-way paper chromatography to separate a mixture of two coloured food dyes, X and Y, using water as the solvent. The solvent front moves 8.0 cm from the pencil start line. The centre of the spot for dye X is 3.2 cm from the start line and the centre of the spot for dye Y is 5.6 cm from the start line.
Explain why dye Y travels further up the paper than dye X.2 marks
A sports laboratory tests an athlete's urine sample for a banned stimulant using gas chromatography combined with mass spectrometry (GC-MS). A peak with retention time 4.2 minutes matches the retention time of a standard sample of the stimulant, which has the formula C₁₀H₁₅N. The mass spectrometer gives a molecular ion peak at m/z 149.1201 for this peak. Accurate relative atomic masses: H = 1.0078, C = 12.0000, N = 14.0031, O = 15.9949.
Explain why combining gas chromatography with mass spectrometry gives a more reliable identification of the stimulant than gas chromatography alone.3 marks

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).