Deck 2: Spectral Techniques

Question 1

In comparing nephelometry and turbidity, nephelometric measurements should demonstrate ______ sensitivity, and turbidimetric measurements should demonstrate ______ sensitivity.In practice, turbidimetric measurements have been found to demonstrate ______ sensitivity.

A)high, limited, high
B)high, limited, limited
C)limited, high, high
D)limited, high, limited

Answer 1

high, limited, high

Question 2

If a glucose standard has an absorbance of 0.480, and an unknown has an absorbance of 0.120, which of the following best describes the unknown's glucose concentration?

A)one fourth the standard concentration
B)equal to the standard concentration
C)four times the standard concentration
D)not enough data to calculate

Answer 2

one fourth the standard concentration

Question 3

A solution of chloramphenicol (MW 323.1) in water gave an absorbance of 0.610 at 278 nm in a 1-cm cuvette; the concentration was 0.02 mg/mL.What is the molar absorptivity of chloramphenicol?

A)30.5 L/mol•cm
B)3050 L/mol•cm
C)9855 L/mol•cm
D)11241 L/mol•cm

Answer 3

9855 L/mol•cm

Question 4

Any radiant energy that is measured by the detector but outside the spectral region isolated by the monochromator of the instrument is referred to as ______.As this increases, Beer's law linearity will ______.

A)Rayleigh scatter, increase
B)stray light, decrease
C)transmitted light, increase
D)polychromatic light, decrease

Question 5

Once a molecule absorbs electromagnetic radiation, it becomes unstable and spontaneously returns to its unexcited, or ground, state by which of the following processes?

A)release of kinetic energy
B)release of vibrational energy
C)release of light energy
D)all of the above

Question 6

The wavelength of electromagnetic radiation is:
1)directly proportional to the energy of a photon
2)inversely proportional to the energy of a photon
3)directly proportional to the frequency of a photon
4)inversely proportional to the frequency of a photon

A)1, 3
B)2, 4
C)1, 4
D)2, 3

Question 7

A system in which the light intensity of the wavelength produced by each atom is directly proportional to the number of atoms emitting energy, which in turn is directly related to the concentration of the compound being measured, describes:
1)atomic absorption spectrophotometry
2)atomic emission flame photometry
3)UV/Visible spectrophotometry
4)fluorometry

A)1, 2, 3, 4
B)1, 2, 3
C)1, 3
D)2, 4

Question 8

Absorbance is _________ related to percent transmittance.

A)directly
B)inversely
C)directly and logarithmically
D)inversely and logarithmically

Question 9

In the clinical laboratory, the primary problem with the use of fluorescent techniques is that:

A)this technique is not a very sensitive technique as compared to other spectrophotometric techniques.
B)the flame may not be hot enough to totally dissociate some of the complexes.
C)many compounds do not fluoresce in their natural state.
D)all of the stray light produced in the instrument cannot be filtered out.

Question 10

The percent transmittance of a solution is 50%.Calculate the absorbance.

A)3.7
B)1.7
C)0.7
D)0.3

Question 11

In UV/Visible spectrophotometry, absorption spectra consist of relatively broad bands of absorption, whereas in atomic absorption spectrophotometry, line spectra consist of lines of absorption that are on the order of 0.001 to 0.01 nm in width.Which of the following provides the correct explanation for this difference in width of absorption bands?

A)The methods of detection in atomic absorption spectrophotometry are much more sensitive than those utilized in UV/Visible spectrophotometry.
B)Atomic absorption methods measure absorption characteristics of vaporized atoms, whereas UV/Visible techniques measure absorption characteristics of molecules with many bonds and chromophoric groups.
C)The use of the flame in atomic absorption methods removes the matrix which causes broad absorption bands in UV/Visible techniques.
D)The use of the flame in atomic absorption methods removes chemical interferences that would otherwise broaden absorption bands.

Question 12

A linear relationship between concentration and fluorescence intensity is seen as long as solutions being quantified have an absorbance of:

A)less than 0.100
B)less than 0.500
C)greater than 0.500
D)greater than 1.000

Question 13

What would happen to the percent transmittance of a sample that was read in a cuvette with fingerprints on the optical surface?

A)%T would increase
B)%T would decrease
C)%T of quartz cuvettes would not be affected by fingerprints
D)%T of glass cuvettes would not be affected by fingerprints

Question 14

As part of the development of a new spectrophotometric assay, an absorption spectrum was recorded.Which of the following describes the purpose for this absorption spectrum?

A)to determine the appropriate wavelength of analysis for the assay
B)to determine the maximal concentration that can be accurately measured for the assay
C)to check for stray light
D)to check for linearity

Question 15

The light source most frequently used for spectrophotometric analysis in the UV region is a ______ lamp and in the visible region, a _____ lamp.

A)tungsten, mercury vapor
B)deuterium, tungsten
C)mercury vapor, deuterium
D)tungsten, deuterium

Question 16

Suppose the absorbance for a known solution was calculated to be 0.333.The solution was measured on a spectrophotometer, and the measured absorbance was 0.321.The solution was prepared again and gave the same absorbance reading of 0.321.Which of the following explanations would most accurately explain the difference between the calculated absorbance and the measured absorbance?

A)Calculated absorbance is only an estimate of the true absorbance measured by spectrophotometry.
B)The molar absorptivity of the compound changes over the bandpass of the spectrophotometer.
C)There may have been an error in the preparation of the solution measured by spectrophotometry.
D)Measured absorbance is only an estimate of the true absorbance determined by mathematical calculations.

Question 17

What are the units for a (absorptivity) in Beer's law when c (concentration) is expressed in g/dL, and b (path length) is expressed in cm?

A)cm/g•dL
B)g/dL•cm
C)dL/g•cm
D)absorptivity is a unitless term

Question 18

The flame in atomic absorption spectrophotometry is used to:

A)provide excitation energy for the atom being measured
B)dissociate the ionic form of the element from its chemical bonds
C)place the ionic form of the element in the atomic ground state
D)both b and c

Question 19

Holmium oxide and didymium filters are used to perform which of the following quality-control checks on spectrophotometers?

A)wavelength accuracy
B)linearity of detector response
C)stray light
D)photometric accuracy

Question 20

______ techniques measure light scattered by a particulate solution, and ______ techniques measure a decrease in light transmission through a particulate solution._____ measurements can be performed on a basic UV/Visible spectrophotometer.

A)turbidimetric, nephelometric, nephelometric
B)turbidimetric, nephelometric, turbidimetric
C)nephelometric, turbidimetric, nephelometric
D)nephelometric, turbidimetric, turbidimetric