Chapter 4 Multiple Choice Questions

. Which of the following statements best describes resolving power?

(m/z)/(Δ(m/z))

Δ(m/z) at a specified value of m/z

The power of mass spectrometry to resolve an analytical problem

Mass analyser scan speed

. A mass spectrum exhibits a FWHM peak width of Δ(m/z) = 0.040 at m/z 850. What is the resolution seen in the spectrum (to 2 significant figures)?

4.2 x 10^-5

34

21,000

25,000

. Two ions of m/z = 545.33 and m/z = 545.51 are just resolved at 10 % valley. What is the resolution seen in the spectrum (to 2 significant figures)?

1,500

15,000

30,000

3,000

. An ion of formula [M+H]⁺ = C₁₁H₁₆NO₂ has a measured value of m/z = 194.1180. If the exact theoretical mass of the ion is 194.1176, what is the mass error in ppm?

0.5

2.1

5.0

1.2

. Achieving high mass accuracy (< 1 ppm) is particularly important when determining the elemental composition of ions with larger molecular mass because:

the number of possible formulae scales exponentially with increasing molecular mass

more importance is attached to the analysis of larger molecules

the number of possible formulae scales linearly with increasing molecular mass

larger molecules are always more difficult to analyse

. Define the term 'sensitivity' in the context of mass spectrometry

Sensitivity is the slope of the curve which relates ion abundance and concentration when a specific compound is analysed.

Sensitivity is the number of ions produced by the ion source.

Sensitivity is the number of ions which arrive at the detector.

Sensitivity is the lowest amount of sample that just enable the signal to be distinguished from background noise.

. Name an approach to increase sensitivity for an intact analyte ion using a 'beam type' mass analyser.

Single reaction monitoring (SRM)

Multiple reaction monitoring (MRM

Selected ion monitoring (SIM)

Reaction monitoring (RM)

. What does the term LLOQ stand for?

Lower limit of quantification

Lower limit of detection

Limit of quantification

Limit of detection

. Why does higher resolution sometimes lead to poorer sensitivity in a mass spectrometer?

To achieve higher resolution fewer ions are generated in the ion source.

Sensitivity is dependent on mass accuracy which is increased when the resolution is lower.

Higher resolution is achieved by switching the detector from sensitivity to resolution mode.

The ion beam is focussed more precisely and this process attenuates the number of ions that can reach the detector.

. Which of the following best defines the sensitivity of analysis by a mass spectrometer?

The relationship between how many ions are produced in the mass spectrometer and the number detected.

The slope of the curve relating total ion intensity and analyte concentration.

The limit of detection

The limit of quantification

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