Worksheet: UV–Vis Spectroscopy Methods

In this worksheet, we will practice choosing a UV–vis spectroscopic method and comparing the features and limitations of different spectrometers.

Q1:

In what phase is basic UV–visible spectroscopy designed to analyze samples?

  • APlasma phase
  • BSolid (or suspension) phase
  • CGas phase
  • DSolution (or liquid) phase

Q2:

Which of the following statements about UV–visible spectrophotometers is not true?

  • ADeuterium or tungsten lamps are commonly used as light sources.
  • BSingle-beam and double-beam instruments contain a filter for selecting one wavelength at a time.
  • CA simultaneous UV–vis instrument contains mirrors and a monochromator in order to allow simultaneous detection at various wavelengths.
  • DA diode array detector eliminates the need for a monochromator.

Q3:

Which of the following can not be detected by fluorescence or phosphorescence spectroscopy?

  • APharmaceuticals
  • BVitamins
  • CEnvironmental pollutants
  • DUncomplexed metal ions

Q4:

Which of the following are the analytical methods turbidimetry and nephelometry based on?

  • ALight scattering
  • BPhoton emission
  • CParamagnetism
  • DNuclear repulsion
  • EPhoton absorption

Q5:

How does turbidimetry differ from nephelometry?

  • ANephelometry measures the total metal ion, or inorganic, content; turbidimetry measures total organic content.
  • BTurbidimetry measures the decrease in transmittance of incident radiation; nephelometry measures the intensity of scattered radiation.
  • CNephelometry measures the decrease in transmittance of incident radiation; turbidimetry measures the intensity of scattered radiation.
  • DTurbidimetry measures the total metal ion, or inorganic, content; nephelometry measures total organic content.
  • EThe terms are synonymous; there is no difference.

Q6:

In which phase does flame atomic absorption measure absorption of radiation of analytes?

  • AAqueous phase
  • BGas phase
  • CLiquid (neat) phase
  • DPlasma phase
  • ESolid phase

Q7:

Why are fluorescence and phosphorescence spectra measured at a 90 degree angle to the source?

  • ABecause the processes of fluorescence and phosphorescence are too intense to observe directly.
  • BBecause the monochromator directs the light at a 90 degree angle.
  • CTo ensure that incident (source) photons are not observed.
  • DBecause the sample cell is darkened on two adjacent sides.
  • ETo make the overall instrument smaller.

Q8:

Why is fluorescence spectroscopy often carried out in a liquid nitrogen environment?

  • APhosphorescent molecules tend to also have explosive properties.
  • BThe detector requires lower temperatures for operation.
  • CThe monochromator slows down the radiation before it hits the sample.
  • DThe source radiation can overheat and destroy the analyte.
  • EPhosphorescence is more likely to occur at low temperatures in a viscous medium.

Q9:

In size exclusion chromatography, what happens to the larger particles?

  • AThey elute first, before smaller particles.
  • BThey remain on the column longer than smaller particles.
  • CThey bind permanently to the stationary phase.
  • DThey are broken down into smaller particles.
  • EThey become oxidized as they move through the column.

Q10:

Which of the following is the correct order in which light passes through a UV–vis spectrometer?

  • ASource, monochromator, sample, detector
  • BDetector, sample, source, monochromator
  • CMonochromator, source, sample, detector
  • DSource, sample, monochromator, detector
  • ESample, source, monochromator, detector

Q11:

What is the purpose of a monochromator?

  • ATo remove stray light from the room
  • BTo allow only light of a certain wavelength to pass from the source to the sample
  • CTo focus light from the sample onto the detector
  • DTo serve as a polychromatic light source
  • ETo interpret the photon signal into a digital readout

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