Question 1

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?

Accepted Answer

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. B

Question 2

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?

Accepted Answer

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 A

Question 3

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

Accepted Answer

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

Question 4

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

Accepted Answer

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

Question 5

The flame in atomic absorption spectrophotometry is used to:

Accepted Answer

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 6

______ 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.

Accepted Answer

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

Question 7

Absorbance is _________ related to percent transmittance.

Accepted Answer

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

Question 8

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?

Accepted Answer

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 9

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?

Accepted Answer

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

Question 10

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

Accepted Answer

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 11

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

Accepted Answer

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

Question 12

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

Accepted Answer

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

Question 13

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

Accepted Answer

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

Question 14

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?

Accepted Answer

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

Question 15

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.

Accepted Answer

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

Question 16

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 ______.

Accepted Answer

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

Question 17

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

Accepted Answer

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

Question 18

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

Accepted Answer

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 19

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?

Accepted Answer

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

Question 20

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

Accepted Answer

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

Exam 2: Spectral Techniques