Deck 4: Chromatographic Techniques

Question 1

What is the purpose of adding an amine modifier (such as triethylamine) to the mobile phase when using a silica-based reversed-phase stationary phase for the chromatography of basic compounds?

A)to help dissolve the basic compounds in the mobile phase
B)to adjust the pH of the mobile phase to the desired basic pH
C)to block free silanol sites on the stationary phase from reacting with the basic solutes
D)to establish a flat baseline for spectrophotometric measurements

Answer 1

to block free silanol sites on the stationary phase from reacting with the basic solutes

Question 2

Suppose there is a desire to analyze a series of compounds by gas chromatography because of their similarity in polarity and lack of hydrogen-bonding potential.The compounds of interest are known to have low volatility.How should the technologist proceed?

A)Consider analysis of these compounds by liquid chromatography.
B)Consider analysis of these compounds by gas chromatography at significantly elevated temperatures.
C)Consider chemical derivatization of these compounds prior to gas chromatography.
D)Report that these compounds cannot be analyzed by gas chromatography because of the lack of volatility.

Answer 2

Consider chemical derivatization of these compounds prior to gas chromatography.

Question 3

Which of the following are required characteristics of the carrier gas used in gas chromatography?

A)It must be chemically and chromatographically inert.
B)It must be pure and dry.
C)It must be matched with the appropriate gas-chromatographic detector.
D)All of the above

Answer 3

All of the above

Question 4

__________ is the most important parameter influencing separation in gas chromatography.

A)carrier gas flow rate
B)column temperature
C)injection volume
D)analyte polarity

Question 5

The three most common HPLC detectors used in the clinical laboratory are absorbance, fluorescence, and electrochemical detectors.What is the most important limitation of these detectors?

A)These detectors will provide semi-quantitative data only.
B)These detectors will provide preliminary solute identification only.
C)These detectors will not provide a linear relationship between detector output (e.g., absorbance) and concentration.
D)These detectors lack the needed sensitivity to be useful in clinical laboratory analysis.

Question 6

Which of the following components of the gas chromatograph does not require close temperature control?

A)the carrier gas
B)the injector port
C)the column
D)the detector

Question 7

What is meant by the phrase isocratic analysis in liquid chromatography?

A)chromatographic analysis in which the mobile phase composition constantly changes during the chromatographic analysis
B)chromatographic analysis in which the mobile phase composition remains constant during the chromatographic analysis
C)chromatographic analysis in which the temperature of the stationary phase constantly changes during the chromatographic analysis
D)chromatographic analysis in which the temperature of the stationary phase remains constant during the chromatographic analysis

Question 8

Suppose there is the need to separate the components of a mixture in which the components are known to have a molecular weight of less than 1000 D, not be ionizable, and be relatively nonpolar with limited hydrogen-bonding potential.Which chromatographic method should be selected?

A)adsorption chromatography
B)partition chromatography
C)ion-exchange chromatography
D)gel-permeation chromatography

Question 9

Which of the following gas chromatographic detectors requires that the analyte be flammable for detection to occur?

A)thermal-conductivity detector
B)flame-ionization detector
C)electron-capture detector
D)mass-spectrometer detector

Question 10

Match the following statements with normal-phase chromatography or reversed-phase chromatography.
1)The more polar the mobile phase, the weaker the mobile phase.
2)The more polar the mobile phase, the stronger the mobile phase.
3)The more nonpolar the mobile phase, the weaker the mobile phase.
4)The more nonpolar the mobile phase, the stronger the mobile phase.

A)1 and 4 are correct for normal-phase chromatography
B)2 and 3 are correct for normal-phase chromatography
C)1 and 3 are correct for reversed-phase chromatography
D)2 and 4 are correct for reversed-phase chromatography

Question 11

In mass spectrometry, the molecular ion is:

A)the ion of highest relative abundance in the spectrum
B)the ion from which all other fragment ions are derived
C)always observed in the mass spectrum
D)all of the above

Question 12

Which of the following types of chromatography should be selected to separate relatively large molecules (100,000 D or greater)?

A)adsorption chromatography
B)partition chromatography
C)ion-exchange chromatography
D)gel-permeation chromatography

Question 13

Which of the following gas-chromatographic detectors is known to be the least sensitive but the most versatile?

A)thermal-conductivity detector
B)flame-ionization detector
C)nitrogen-phosphorus detector
D)electron-capture detector

Question 14

The chromatographic method based on biologically related interactions by immobilizing one of a pair of interacting biomolecules onto a solid support and placing it in a column is known as:

A)affinity chromatography
B)ion-suppression chromatography
C)ion-pair chromatography
D)gel-permeation chromatography

Question 15

Which of the following techniques is the most advantageous technique for separating enantiomers by chromatography?

A)use of a chiral stationary phase specifically designed for the enantiomeric pair
B)use of a mobile phase containing a chiral complexing agent which forms diastereomeric complexes during the chromatographic analysis
C)chemical derivatization of the enantiomeric pair, forming diastereomers prior to chromatographic analysis
D)chemical derivatization of the enantiomeric pair, forming diastereomers following chromatographic analysis

Question 16

Given that the base peak (m/z = 112) in a mass spectrum has an initial relative abundance of 75% and the peak at m/z 125 has an initial relative abundance of 30%, what will be the relative abundance of the two peaks following normalization? (answer format: relative abundance for m/z 112, relative abundance for m/z 125)

A)22.5%, 100%
B)250%, 100%
C)100%, 22.5%
D)100%, 40%

Question 17

Which of the following is the correct order of sensitivity for HPLC detectors? (most sensitive to least sensitive)

A)absorbance, fluorescence, electrochemical
B)fluorescence, absorbance, electrochemical
C)electrochemical, fluorescence, absorbance
D)absorbance, electrochemical, fluorescence

Question 18

_____ mass spectrometry is more likely to reveal the molecular weight of the molecule being analyzed, and ______ mass spectrometry is more likely to reveal structural details of the molecule being analyzed._____ mass spectrometry is considered to be the more sensitive of the two techniques by several orders of magnitude.(CI = chemical-ionization; EI = electron-ionization)

A)CI, EI, CI
B)CI, EI, EI
C)EI, CI, CI
D)EI, CI, EI

Question 19

Combining selected ion monitoring (SIM) with isotope dilution in electron-ionization mass spectrometry allows:

A)for the removal of extraneous ions that produce complicating peaks in the mass spectrum
B)for quantification utilizing an internal standard
C)for confirmation of results obtained by electron-ionization mass spectrometry alone
D)for quality control checks on the mass spectrometry procedure

Question 20

Which of the following identifies a purpose for the use of internal standardization in chromatography?

A)It compensates for loss during sample preparation, injection imprecision, and detector variation.
B)It allows for analyte quantification.
C)It serves as a quality-control check.
D)All of the above