MChem Master of Chemistry Master of Chemistry: Analytical Chemistry 4

Question 1

In gas chromatography, the Kovats retention index is used to:

Accepted Answer

Express analyte retention relative to n-alkane standards

Answer

The Kovats retention index expresses analyte retention as a linear interpolation between bracketing n-alkanes, making retention data transferable across columns and labs.

Question 2

Which technique directly measures the mass of an adsorbed film with nanogram sensitivity by monitoring changes in resonant frequency?

Accepted Answer

Quartz crystal microbalance (QCM)

Answer

QCM uses the Sauerbrey equation, which relates frequency decrease linearly to added mass on a piezoelectric quartz crystal oscillator.

Question 3

In 2D NMR, a COSY experiment correlates nuclei that are:

Accepted Answer

Scalar (J) coupled to each other through bonds

Answer

COSY (COrrelation SpectroscopY) identifies proton pairs connected through scalar (J) coupling, typically 2-4 bonds apart.

Question 4

What is the purpose of using an internal standard in quantitative analytical measurements?

Accepted Answer

To correct for variations in sample preparation and instrument response

Answer

An internal standard compensates for losses during sample preparation and instrument fluctuations by normalizing the analyte signal to the internal standard signal.

Question 5

In potentiometric pH measurement, a glass electrode develops a potential primarily because of:

Accepted Answer

Ion exchange of H+ ions at the hydrated gel layer of the glass membrane

Answer

The glass membrane potential arises from selective H+ exchange between solution and the hydrated silicate gel layer, generating a Nernstian response.

MChem Master of Chemistry Practice Test

MChem Master of Chemistry Practice Test

MChem Master of Chemistry Master of Chemistry: Analytical Chemistry 4