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.
In what phase is basic UV–visible spectroscopy designed to analyze samples?
- APlasma phase
- BSolid (or suspension) phase
- CGas phase
- DSolution (or liquid) phase
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.
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.
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.
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.
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.
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
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