Deck 26: High-Performance Liquid Chromatography

Question 1

As particle size decreases for HPLC,the required solvent pressure____________________ ,the plate number____________________ ,and the resolution____________________ ?

A)increases;increases;decreases
B)decreases;decreases;increases
C)increases;increases;increases
D)increases;decreases;decreases
E)decreases;increases;increases

Answer 1

increases;increases;increases

Question 2

Gradient elution is used in HPLC.How is the gradient created for a reverse-phase HPLC experiment?

A)Increase the pH of the mobile phase over time by adding strong base.
B)Decrease the pH of the mobile phase over time by adding strong acid.
C)Increase the vapor pressure of the analytes over time by increasing the temperature.
D)Increase the polarity of the mobile phase over time by mixing with a more polar solvent.
E)Decrease the polarity of the mobile phase over time by mixing with a less polar solvent.

Answer 2

Decrease the polarity of the mobile phase over time by mixing with a less polar solvent.

Question 3

The________________________________________responds to analytes that are significantly less volatile than the mobile phase.

A)electrochemical detector
B)ultraviolet detector
C)refractive index detector
D)evaporative light-scattering detector
E)thermal conductivity detector

Answer 3

evaporative light-scattering detector

Question 4

What is the plate height for a 10.0-cm HPLC column packed with 3.5 m solid phase?

Question 5

During method optimization,the relative retention is adjusted by altering all of the following,except:

A)column temperature.
B)type of organic solvent.
C)solvent composition.
D)adjusting sample injection volume.
E)column type.

Question 6

A________________________________________is a gradient developed to retain the resolution of a single gradient,but reduces the analysis time.

A)broken gradient
B)segmented gradient
C)choppy gradient
D)step gradient
E)parcel gradient

Question 7

The pressure required to push solvent through the column is dependent on several variables such as column length,particle diameter,etc.For column pressure,which relationship is INCORRECT?

A)Pressure is inversely proportional to column length.
B)Pressure is directly proportional to solvent viscosity.
C)Pressure is inversely proportional to particle diameter squared.
D)Pressure is inversely proportional to column radius squared.
E)Pressure is directly proportional to volume flow rate.

Question 8

Which statement(s)is(are)NOT true for partition and adsorption chromatography?
I For adsorption chromatography - the lower the eluent strength of the solvent,the more easily it displaces the solute.
II For partition chromatography - the more time the solute spends in the mobile phase,the easier it is to elute.
III For partition chromatography - solute equilibrates between the mobile phase and the liquid phase bonded to the solid support.
IV For adsorption chromatography - solvent molecules compete with solute molecules for binding sites on the stationary phase.

A)IV
B)I
C)III and IV
D)II
E)I and II

Question 9

The________________________________________is a sensitive,almost universal detector that responds to all nonvolatile compounds,regardless of their structure.

A)electrochemical detector
B)charged aerosol detector
C)refractive index detector
D)evaporative light-scattering detector
E)thermal conductivity detector

Question 10

____________________ is the volume between the point at which the solvents are mixed and the beginning of the column.Which is NOT true for dwell volume and dwell time?

A)If the dwell time is 5 minutes,a solvent change initiated at 9 minutes does not reach the column until 14 minutes.
B)A difference in dwell volumes is the main reason why gradient separations do not always transfer well between instruments.
C)Dwell volume is the volume between where solvents are mixed and the beginning of the column.
D)The product of the dwell volume and the flow rate is the dwell time.
E)It is helpful to indicate the dwell volume when reporting a gradient separation.

Question 11

Which of the following is NOT a detector used with HPLC?

A)electrochemical detector
B)ultraviolet detector
C)refractive index detector
D)evaporative light-scattering detector
E)thermal conductivity detector

Question 12

The________________________________________creates gradients from up to four solvents by proportioning liquids through a four-way valve before the piston and then pumped into the column.

A)high-pressure mixing pump
B)multiple source mixing pump
C)low-pressure mixing pump
D)gradient mixing pump
E)variable composition mixing pump

Question 13

Elution with a constant composition mobile phase is:

A)constant polarity elution.
B)isopolar elution.
C)isocratic elution.
D)homogeneous elution.
E)true elution.

Question 14

Which of the following are characteristics of reverse-phase chromatography?
I The stationary phase is polar.
II The mobile phase is more polar than the stationary phase.
III Less polar mobile phase has a lower eluent strength.
IV More polar mobile phase has a higher eluent strength.
V The stationary phase is nonpolar.

A)I and IV
B)II only
C)I and III
D)II and IV
E)II and V

Question 15

Which of the following is NOT true for HPLC sample injection.

A)Reproducibly load injector loop with < 0.5 or > 3 loop volumes depending on injection technique.
B)The injection loops must be removed and cleaned after each injection.
C)Sample solvent strength should be less than or equal to eluent solvent strength.
D)Pass samples through a 0.5-m filter to remove particulate matter prior to injection.
E)Use a blunt HPLC syringe needle,not pointed,to prevent damage to the injection port.

Question 16

HPLC operation requires special solvents,HPLC-grade.Additionally,HPLC-grade solvents require pretreatment before use.Which of the following is NOT a characteristic of HPLC-grade solvents or pretreatment required before operation?

A)HPLC-grade solvent prevents degradation of costly columns with impurities.
B)HPLC-grade solvent must be sparged prior to use if the instrument is not equipped with a degrasser.
C)HPLC-grade solvent minimizes background contamination signals in the detector.
D)HPLC-grade solvent must be filtered to remove particulate matter.
E)HPLC-grade solvent must be stored in special cabinetry to prevent solvent degradation.

Question 17

Normal-phase chromatography uses a____________________ stationary phase and a____________________ mobile phase.The more____________________ the mobile phase becomes,the stronger the eluent strength.

A)polar;polar;polar
B)nonpolar;nonpolar;polar
C)polar;nonpolar;nonpolar
D)polar;nonpolar;polar
E)nonpolar;polar;nonpolar

Question 18

The criteria for an adequate separation for isocratic reverse-phase HPLC include which of the following?
I The retention factor for all peaks are in the range of 0.5 - 20.
II All peaks should be symmetric with an asymmetry factor B/A in the range of 0.9 - 15.
III For quantification,the minimum resolution between the two closest peaks should be 1.5,though 2.0 is best to compensate for small changes in separation conditions.
IV The pressure must be less than or equal to 15 MPa to prolong instrument life.

A)I,II,III,and IV
B)I,II,and IV
C)I,II,and III
D)II,III,and IV
E)III and IV

Question 19

What particle diameter is needed to give 15 000 plates over a 10-cm HPLC column?

Question 20

When deciding between an isocratic elution or a gradient elution,a scouting gradient should be done.Which of the criteria below is INCORRECT?

A)If t/t_G < 0.25,use isocratic elution.
B)If t/t_G > 0.40,use gradient elution.
C)For 0.25 < t/t_G < 0.40 use either an isocratic or gradient elution,the decision depending on factors such as available equipment or complexity of the sample.
D)For t/t_G < 0.25,a good starting isocratic elution solvent composition is the composition halfway through the t of the scouting gradient.
E)For 0.25 < t/t_G < 0.40,a good starting isocratic elution solvent composition is the composition halfway through the t_G of the scouting gradient.