Instrumental Analysis Exam 2 questions with
verified answers
Atomic Absorption Spectroscopy Ans✓✓✓ An analytical technique that
uses light absorption to measure the concentration of a metal in a
sample.
Requires flame to atomize samples into ground state atoms.
Atoms absorb characteristic wavelengths from hollow cathode lamps.
Atomic Emission Spectroscopy Ans✓✓✓ A technique in which the
emission of light by thermally excited atoms or ions in a flame, furnace,
or plasma is used to measure concentration.
Requires no lamp.
Intensity proportional to element concentration.
Most common form of atomic spectroscopy.
Atomization Ans✓✓✓ the process of breaking chemical bonds to
decompose a sample into a gas of isolated atoms
Background signal Ans✓✓✓ arises from absorption, emission, or
scatter by everything in the sample besides analyte (the matrix), as well
as from absorption, emission, or scatter by flame, plasma, or furnace.
Characteristic Wavelengths Ans✓✓✓ atoms of each element absorb
and emit light at unique wavelengths
,chemical interference Ans✓✓✓ interference from any component of
the sample that reduces atomization of the analyte. Corrected for by
standard addition method, releasing agents, or protecting agents.
Compare EELS to conventional IR and Raman Spectroscopy. Ans✓✓✓
EELS (electron energy loss spec) consists of a low energy beam of
electrons exciting and scattering off of a sample surface. The energy
loss of some of the scattered electrons is detected and attributed to
vibrational excitation of surface molecules. A vibrational spectrum can
be obtained by plotting the count of energy-loss electrons relative to
elastically scattered electrons against energy which can be used to
identify functional groups and chemical bonds. Advantages include
adequate sample molecule characterization. Limitations include low
resolving power. In contrast, IR spectroscopy excites species with IR
radiation, and the transmitted IR radiation is measured after passing
through the sample to give a vibrational spectrum. Raman spectroscopy
measures the scattered visible radiation after radiation passes through
the sample.
Compare the two most common types of SPM's. Ans✓✓✓ Scanning
tunneling microscope and the atomic force microscope. The STM is a
surface imaging tool based on quantum tunneling of electrons between
surface and STM tip. When conducting tip is brought close to the
surface, bias voltage is applied which causes electrons to tunnel
through the vacuum from the surface to the tip resulting in a tunneling
current that changes with surface height density.
, The AFM consists of a sharp tipped cantilever with a very small tip.
When the tip is close to the surface, forces between tip and surface
lead to deflection of the cantilever according to Hookes law (typically
van der waals forces). Cantilever deflection is measured to get a picture
of the surface.
Advantage of AFM is that it doesn't require conducting samples, and it
has higher resolution. STM can isolate single molecules.
Limitations of STM is that it can only be applied to conducting samples.
For AFM, surface forces may be large enough to damage sample
surface and distort the image.
Describe how it is possible to distinguish between XPS peaks and Auger
electron peaks. Ans✓✓✓ Auger lines are independent of the input
energy because the auger electron energy is independent of the
original photon/electron energy. When comparing spectra produced by
2 x-ray sources, auger lines remain unchanged on the kinetic energy
scale while XPS peaks move.
Describe the changes in state of the metals as they proceed from the
sample container, through the nebulizer and then through the flame.
Ans✓✓✓ In general, the metal molecules are in liquid solutions when
they are introduced into the nebulizer from the sample container via
aspiration. In the nebulizer, nebulization occurs which doesn't affect
the state of matter of the solution but instead turns the solution into an
aerosol of fine droplets. This occurs when an inert Argon gas is flowed
at a high rate through a stream of the solution. This mist is then carried
into the flame with more Argon gas. In the flame, the spray first
evaporates from the heat to leave behind an aerosol containing only
verified answers
Atomic Absorption Spectroscopy Ans✓✓✓ An analytical technique that
uses light absorption to measure the concentration of a metal in a
sample.
Requires flame to atomize samples into ground state atoms.
Atoms absorb characteristic wavelengths from hollow cathode lamps.
Atomic Emission Spectroscopy Ans✓✓✓ A technique in which the
emission of light by thermally excited atoms or ions in a flame, furnace,
or plasma is used to measure concentration.
Requires no lamp.
Intensity proportional to element concentration.
Most common form of atomic spectroscopy.
Atomization Ans✓✓✓ the process of breaking chemical bonds to
decompose a sample into a gas of isolated atoms
Background signal Ans✓✓✓ arises from absorption, emission, or
scatter by everything in the sample besides analyte (the matrix), as well
as from absorption, emission, or scatter by flame, plasma, or furnace.
Characteristic Wavelengths Ans✓✓✓ atoms of each element absorb
and emit light at unique wavelengths
,chemical interference Ans✓✓✓ interference from any component of
the sample that reduces atomization of the analyte. Corrected for by
standard addition method, releasing agents, or protecting agents.
Compare EELS to conventional IR and Raman Spectroscopy. Ans✓✓✓
EELS (electron energy loss spec) consists of a low energy beam of
electrons exciting and scattering off of a sample surface. The energy
loss of some of the scattered electrons is detected and attributed to
vibrational excitation of surface molecules. A vibrational spectrum can
be obtained by plotting the count of energy-loss electrons relative to
elastically scattered electrons against energy which can be used to
identify functional groups and chemical bonds. Advantages include
adequate sample molecule characterization. Limitations include low
resolving power. In contrast, IR spectroscopy excites species with IR
radiation, and the transmitted IR radiation is measured after passing
through the sample to give a vibrational spectrum. Raman spectroscopy
measures the scattered visible radiation after radiation passes through
the sample.
Compare the two most common types of SPM's. Ans✓✓✓ Scanning
tunneling microscope and the atomic force microscope. The STM is a
surface imaging tool based on quantum tunneling of electrons between
surface and STM tip. When conducting tip is brought close to the
surface, bias voltage is applied which causes electrons to tunnel
through the vacuum from the surface to the tip resulting in a tunneling
current that changes with surface height density.
, The AFM consists of a sharp tipped cantilever with a very small tip.
When the tip is close to the surface, forces between tip and surface
lead to deflection of the cantilever according to Hookes law (typically
van der waals forces). Cantilever deflection is measured to get a picture
of the surface.
Advantage of AFM is that it doesn't require conducting samples, and it
has higher resolution. STM can isolate single molecules.
Limitations of STM is that it can only be applied to conducting samples.
For AFM, surface forces may be large enough to damage sample
surface and distort the image.
Describe how it is possible to distinguish between XPS peaks and Auger
electron peaks. Ans✓✓✓ Auger lines are independent of the input
energy because the auger electron energy is independent of the
original photon/electron energy. When comparing spectra produced by
2 x-ray sources, auger lines remain unchanged on the kinetic energy
scale while XPS peaks move.
Describe the changes in state of the metals as they proceed from the
sample container, through the nebulizer and then through the flame.
Ans✓✓✓ In general, the metal molecules are in liquid solutions when
they are introduced into the nebulizer from the sample container via
aspiration. In the nebulizer, nebulization occurs which doesn't affect
the state of matter of the solution but instead turns the solution into an
aerosol of fine droplets. This occurs when an inert Argon gas is flowed
at a high rate through a stream of the solution. This mist is then carried
into the flame with more Argon gas. In the flame, the spray first
evaporates from the heat to leave behind an aerosol containing only
