MChem Master of Chemistry Master of Chemistry: Analytical Chemistry 5

Question 1

Which chromatographic detector responds to virtually all organic compounds but is non-selective and destructive, making it unsuitable for preparative work?

Accepted Answer

Flame ionization detector (FID)

Answer

FID burns analytes in a hydrogen-air flame, producing ions detected as current; it has near-universal response to organic compounds but destroys the sample.

Question 2

In size-exclusion chromatography (SEC), larger molecules elute:

Accepted Answer

First, because they are excluded from the pores of the stationary phase

Answer

Large molecules cannot enter the pores of the SEC packing, so they traverse only the interstitial volume and elute earliest.

Question 3

The Debye-Hückel limiting law describes how ionic strength affects:

Accepted Answer

The mean ionic activity coefficient in dilute electrolyte solutions

Answer

The Debye-Hückel limiting law predicts that log γ± = -A|z+z-|√I for very dilute solutions, showing how ionic atmosphere reduces activity coefficients.

Question 4

In tandem mass spectrometry (MS/MS), what occurs during the 'collision-induced dissociation' (CID) step?

Accepted Answer

The selected precursor ion fragments after collision with neutral gas molecules

Answer

CID activates a mass-selected precursor ion by collisions with an inert gas (e.g., argon), converting kinetic energy into internal energy that drives fragmentation.

Question 5

Which electroanalytical technique applies a linearly varying potential and measures the resulting current to determine analyte concentration from peak current?

Accepted Answer

Linear sweep voltammetry (LSV)

Answer

LSV scans potential linearly with time and records faradaic current peaks whose height is proportional to analyte concentration via the Randles-Ševčík equation.

MChem Master of Chemistry Practice Test

MChem Master of Chemistry Practice Test

MChem Master of Chemistry Master of Chemistry: Analytical Chemistry 5