In this worksheet, we will practice choosing a UV–vis spectroscopic method and comparing the features and limitations of different spectrometers.
Basic UV-Visible spectroscopy is designed to analyze samples in what phase?
- AGas phase
- BSolid (or suspension) phase
- CPlasma phase
- DSolution (or liquid) phase
Which of the following statements about UV-Visible spectrophotometers is not true?
- AA diode array detector eliminates the need for a monochromator.
- BDeuterium or tungsten lamps are commonly used as light sources.
- CSingle-beam and double-beam instruments contain a filter for selecting one wavelength at a time.
- DA simultaneous UV-Vis instrument contains mirrors and a monochromator in order to allow simultaneous detection at various wavelengths.
Which one of the following cannot be detected by fluorescence or phosphorescence spectroscopy?
- AEnvironmental pollutants
- DUncomplexed metal ions
Turbidimetry and nephelometry are analytical methods based on which of the following?
- APhoton absorption
- BPhoton emission
- CNuclear repulsion
- DLight scattering
How does turbidimetry differ from nephelometry?
- ANephelometry measures the total metal ion, or inorganic, content; turbidimetry measures total organic content.
- BNephelometry measures the decrease in transmittance of incident radiation; turbidimetry measures the intensity of scattered radiation.
- CTurbidimetry measures the total metal ion, or inorganic, content; nephelometry measures total organic content.
- DTurbidimetry measures the decrease in transmittance of incident radiation; nephelometry measures the intensity of scattered radiation.
- EThe terms are synonymous; there is no difference.
Flame atomic absorption measures absorption of radiation of analytes in which phase?
- ALiquid (neat) phase
- BSolid phase
- CAqueous phase
- DGas phase
- EPlasma phase
Why are flourescence and phosphorescence spectra measured at a 90 degree angle to the source?
- ABecause the monochromator directs the light at a 90 degree angle.
- BBecause the sample cell is darkened on two adjacent sides.
- CBecause the process of fluorescence and phosphorescence are too intense to observe directly.
- DTo ensure that incident (source) photons are not observed.
- ETo make the overall instrument smaller.
Why is fluorescence spectroscopy often carried out in a liquid nitrogen environment?
- AThe monochromator slows down the radiation before it hits the sample.
- BPhosphorescent molecules tend to also have explosive properties.
- CThe detector requires lower temperatures for operation.
- DPhosphorescence is more likely to occur at low temperatures in a viscous medium.
- EThe source radiation can overheat and destory the analyte.
In size exclusion chromatography, what happens to the larger particles?
- AThey become oxidized as they move through the column.
- BThey are broken down into smaller particles.
- CThey remain on the column longer than smaller particles.
- DThey elute first, before smaller particles.
- EThey bind permanently to the stationary phase.