MChem Master of Chemistry Master of Chemistry: Analytical Chemistry 2 — Questions and Answers
Question 1: Which chromatographic technique is most suitable for separating thermally labile biomolecules such as proteins?
- Gas chromatography (GC)
- High-performance liquid chromatography (HPLC) (Correct answer)
- Supercritical fluid chromatography (SFC)
- Pyrolysis GC
Correct answer: High-performance liquid chromatography (HPLC)
HPLC operates at ambient temperatures in liquid mobile phases, making it ideal for thermally labile biomolecules like proteins.
Question 2: In inductively coupled plasma mass spectrometry (ICP-MS), what is the primary purpose of the collision/reaction cell?
- To ionize the sample
- To remove polyatomic interferences (Correct answer)
- To separate isotopes by mass
- To nebulize the sample solution
Correct answer: To remove polyatomic interferences
The collision/reaction cell uses gases like helium or hydrogen to eliminate polyatomic spectral interferences that overlap with analyte masses.
Question 3: What does the term 'selectivity coefficient' (k_ij) represent in ion-selective electrode (ISE) potentiometry?
- The response slope of the electrode to the primary ion
- The ratio of the electrode's response to an interfering ion versus the primary ion (Correct answer)
- The detection limit of the primary ion
- The diffusion potential across the reference junction
Correct answer: The ratio of the electrode's response to an interfering ion versus the primary ion
The selectivity coefficient k_ij quantifies how strongly an interfering ion j disturbs the electrode's response relative to the primary ion i.
Question 4: In Fourier-transform infrared spectroscopy (FTIR), what is the role of the beamsplitter?
- To focus infrared radiation onto the detector
- To divide the IR beam into two paths for the interferometer (Correct answer)
- To filter out near-IR wavelengths
- To modulate the source intensity
Correct answer: To divide the IR beam into two paths for the interferometer
The beamsplitter in a Michelson interferometer divides the IR beam between the fixed and moving mirrors, creating constructive and destructive interference.
Question 5: Which statistical test is used to compare the precision (variance) of two analytical methods?
- Student's t-test
- F-test (Correct answer)
- Chi-squared test
- ANOVA
Correct answer: F-test
The F-test compares the ratio of two sample variances to determine if the precisions of two methods differ significantly.
Question 6: In electrospray ionization (ESI) mass spectrometry, multiply charged ions are commonly observed. For a protein of molecular weight 10,000 Da carrying 10 protons, what is the observed m/z?
- 10,000
- 1,001 (Correct answer)
- 1,000
- 999
Correct answer: 1,001
With 10 protons added (each +1 Da), m/z = (10,000 + 10×1)/10 = 10,010/10 = 1,001.
Question 7: Which phenomenon describes the shift of NMR resonance frequency of a nucleus due to the surrounding electron density?
- Nuclear Overhauser effect
- Chemical shift (Correct answer)
- Spin-spin coupling
- Relaxation
Correct answer: Chemical shift
Chemical shift reflects how the local electron density shields a nucleus from the external magnetic field, altering its resonance frequency.
MChem Master of Chemistry Master of Chemistry: Analytical Chemistry 2
Which chromatographic technique is most suitable for separating thermally labile biomolecules such as proteins?