ACS CP Analytical Chemistry & Instrumentation 2

Question 1

In atomic absorption spectroscopy (AAS), what is the primary purpose of the hollow cathode lamp?

Accepted Answer

To emit a narrow line spectrum characteristic of the analyte element

Answer

The hollow cathode lamp emits a narrow-line spectrum specific to the cathode element, providing radiation at exactly the wavelength absorbed by the analyte atoms.

Question 2

Which ionization technique in mass spectrometry is considered a 'soft' ionization method that preserves the molecular ion?

Accepted Answer

Electrospray ionization (ESI)

Answer

Electrospray ionization (ESI) is a soft ionization technique that produces multiply charged ions with minimal fragmentation, preserving the intact molecular ion.

Question 3

In gas chromatography, the van Deemter equation describes the relationship between plate height (H) and mobile phase velocity (u). Which term accounts for longitudinal diffusion?

Accepted Answer

B/u term

Answer

The B/u term in the van Deemter equation represents longitudinal (axial) diffusion of solute along the column, which decreases as mobile phase velocity increases.

Question 4

A potentiometric sensor uses a glass electrode to measure pH. The Nernst equation predicts a slope of approximately how many mV per pH unit at 25°C?

Accepted Answer

59.2 mV/pH unit

Answer

At 25°C, the Nernst slope for a monovalent ion (H⁺, n=1) is RT/F × ln(10) ≈ 59.16 mV per decade of activity change.

Question 5

In HPLC, what does a high tailing factor (T > 1.5) for a chromatographic peak typically indicate?

Accepted Answer

Strong secondary interactions between analyte and stationary phase

Answer

Peak tailing (T > 1.5) is usually caused by secondary interactions such as ionic or adsorptive interactions between the analyte and active sites on the stationary phase.

(ACS CP) American Chemical Society (ACS) Certified Professional Practice Test

(ACS CP) American Chemical Society (ACS) Certified Professional Practice Test

ACS CP Analytical Chemistry & Instrumentation 2