ACS CP Analytical Chemistry & Instrumentation 3

Question 1

In X-ray fluorescence (XRF) spectrometry, the energy of the emitted characteristic X-ray is determined by:

Accepted Answer

The difference in binding energies between the electron shells involved in the transition

Answer

Characteristic X-ray energy equals the difference in electron binding energies between the two shells involved (e.g., Kα = EK − EL), making it unique to each element.

Question 2

In capillary electrophoresis (CE), electroosmotic flow (EOF) results from:

Accepted Answer

The movement of the diffuse double layer of cations near the negatively charged capillary wall

Answer

EOF arises when the applied electric field drives the excess cations in the diffuse double layer near the negatively charged silica wall, dragging the bulk solution toward the cathode.

Question 3

Which of the following describes the correct definition of the detection limit (LOD) according to IUPAC guidelines?

Accepted Answer

The signal equal to three times the standard deviation of the blank (3σ blank)

Answer

IUPAC defines the LOD as the analyte concentration corresponding to a signal equal to the blank signal plus 3 times the standard deviation of the blank (k=3, 99.86% confidence).

Question 4

In NMR spectroscopy, the chemical shift is referenced against an internal standard. What compound is most commonly used as the reference standard in ¹H NMR?

Accepted Answer

Tetramethylsilane (TMS, δ = 0.00 ppm)

Answer

Tetramethylsilane (TMS) is the universal ¹H NMR reference standard set at 0.00 ppm because it gives a single sharp peak in a chemically clean region, is inert, and is easily removed.

Question 5

A flame photometer measures lithium content in a serum sample. Which interferent must be most carefully controlled due to its spectral overlap with the lithium emission line at 671 nm?

Accepted Answer

Sodium (589 nm)

Answer

Sodium, though emitting primarily at 589 nm, can cause background interference; more critically, high sodium concentrations cause matrix effects that alter lithium emission intensity.

(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 3