Instrumental Analysis Quiz 3 questions with verified
answers
An analyst attempts to determine strontium with an atomic absorption
instrument equipped with a nitrous oxide-acetylene burner, but the
sensitivity associated with the 460.7-nm atomic resonance line is not
satisfactory. Suggest at least three things that might be tried to
increase sensitivity. Ans✓✓✓ 1) Lower temperature flame to reduce
ionization
2) Use a solvent containing ethanol or another organic substance
3) Add a releasing agent, protective agent or ionization supressor.
Analyte Ans✓✓✓ The substance to be measured or analyzed. The rest
of the sample is the matrix.
Blaze Angle Ans✓✓✓ The angle of most efficient diffraction
Chemical interference Ans✓✓✓
Coherent Radiation Ans✓✓✓ wave trains that have identical
frequencies and phase relationships that are constant with time.
Critical Angle Ans✓✓✓ Angle of total internal reflection
, Describe a method for determining the number of plates in a column.
Ans✓✓✓ The number of plates in a column can be determined by
measuring the retention time Tr and width of a peak at its base W. The
number of plates N is then N = 16(Tr/W)^2
Describe how a deuterium lamp can be used to provide a background
correction for an atomic absorption spectrum. Ans✓✓✓ The radiation
from a D2 lamp is passed through the flame alternately with the hollow
cathode beam. Since the atomic lines are very narrow, the D2 lamp is
mostly absorbed by the background whereas the hollow cathode
radiation is absorbed by the atoms. By comparing the radiant power of
the two beams, the atomic absorption can be corrected for any
background absorption.
Describe the difference between gaseous field ionization sources and
field desorption sources. Ans✓✓✓ in field ionization, the sample is
volatilized before ionization, whereas field desorption takes place at an
anode that has been coated with the sample.
Describe three general methods for improving resolution in partition
chromatography Ans✓✓✓ 1) Adjustment of Ka and Kb
2) Variation in chemical composition to make alpha larger
3) Employing a different packing that makes alpha greater
Describe three ways of introducing a sample into an ICP torch.
Ans✓✓✓ Nebulization, Electrothermal Vaporization or Laser Ablation
answers
An analyst attempts to determine strontium with an atomic absorption
instrument equipped with a nitrous oxide-acetylene burner, but the
sensitivity associated with the 460.7-nm atomic resonance line is not
satisfactory. Suggest at least three things that might be tried to
increase sensitivity. Ans✓✓✓ 1) Lower temperature flame to reduce
ionization
2) Use a solvent containing ethanol or another organic substance
3) Add a releasing agent, protective agent or ionization supressor.
Analyte Ans✓✓✓ The substance to be measured or analyzed. The rest
of the sample is the matrix.
Blaze Angle Ans✓✓✓ The angle of most efficient diffraction
Chemical interference Ans✓✓✓
Coherent Radiation Ans✓✓✓ wave trains that have identical
frequencies and phase relationships that are constant with time.
Critical Angle Ans✓✓✓ Angle of total internal reflection
, Describe a method for determining the number of plates in a column.
Ans✓✓✓ The number of plates in a column can be determined by
measuring the retention time Tr and width of a peak at its base W. The
number of plates N is then N = 16(Tr/W)^2
Describe how a deuterium lamp can be used to provide a background
correction for an atomic absorption spectrum. Ans✓✓✓ The radiation
from a D2 lamp is passed through the flame alternately with the hollow
cathode beam. Since the atomic lines are very narrow, the D2 lamp is
mostly absorbed by the background whereas the hollow cathode
radiation is absorbed by the atoms. By comparing the radiant power of
the two beams, the atomic absorption can be corrected for any
background absorption.
Describe the difference between gaseous field ionization sources and
field desorption sources. Ans✓✓✓ in field ionization, the sample is
volatilized before ionization, whereas field desorption takes place at an
anode that has been coated with the sample.
Describe three general methods for improving resolution in partition
chromatography Ans✓✓✓ 1) Adjustment of Ka and Kb
2) Variation in chemical composition to make alpha larger
3) Employing a different packing that makes alpha greater
Describe three ways of introducing a sample into an ICP torch.
Ans✓✓✓ Nebulization, Electrothermal Vaporization or Laser Ablation
