Question 1

____________________ is a plot of detector response versus retention time.

Accepted Answer

A) Spectrum 
B) Electrophoretogram 
C) Chromatogram 
D) Chromospectrum 
E) Elution response C

Question 2

Which comparison of open tubular columns to packed columns is INCORRECT?

Accepted Answer

A) Open tubular columns have higher resolutions than packed columns. 
B) Open tubular columns have increased linear velocity or a longer column or both. 
C) Packed columns have decreased sensitivity. 
D) Packed columns have longer analysis times. 
E) Packed columns have a lower sample capacity. E

Question 3

Calculate the weak acid,HA,concentration that remains in the aqueous phase when 50.0 mL of 0.184 M HA at pH = 4.75 is extracted with 50 mL of toluene three times.The partition coefficient for the extraction is 5.17,favoring toluene.The K_a for HA is 8.0 x 10⁻⁴.

Accepted Answer

72.5% remains or 0.133 M HA remains in the aqueous phase.

Question 4

____________________ is the physical transfer of solute from one phase to another.

Accepted Answer

A) Partitioning 
B) Extraction 
C) Activated transport 
D) Sieving 
E) Miscibility

Question 5

For two separated solutes the F1F1F1S1F1F1F10 = 1.10 and the k₂ = 4.38.How many theoretical plates are required to achieve a resolution of 1.5?

Accepted Answer

The answer of For two separated solutes the F1F1F1S1F1F1F10 =...

Question 6

The van Deemter equation describes plate height in terms of constants A,B,C,and the linear velocity,ux.Which statement is NOT true for the van Deemter equation?

Accepted Answer

A) A takes into account multiple pathways through the column.The value of A is column specific and independent of linear flow. 
B) B takes into account longitudinal diffusion of the analyte in the mobile phase.The value of B is column specific and the impact of B on the plate height is inversely proportional to the linear velocity. 
C) C takes into account equilibrium time between the stationary and mobile phase.The value of C is column specific and the impact of C on plate height is proportional to the linear velocity. 
D) To minimize plate height,the optimal flow rate is the minima for the plot of

Versus flow rate. 
E) Linear velocity is the flow rate of the mobile phase.

Question 7

Which form of chromatography is INCORRECTLY defined?

Accepted Answer

A) adsorption chromatography - solute is adsorbed into solid particles 
B) partition chromatography - solute equilibrates between the stationary liquid and the mobile phase 
C) ion-exchange chromatography - solute ions of the opposite charge are attracted to the stationary phase 
D) molecular exclusion chromatography - solute is separated based on size 
E) affinity chromatography - solute binds to a molecule specific for the solute

Question 8

Which statements are NOT true regarding chromatography?
I The stationary phase is typically a liquid bonded to the inside surface of a capillary or the surface of solid packed in the column.
II The mobile phase entering the column is the eluate.
III Mobile phase is the solvent (gas or liquid)that moves through the column.
IV Eluent is the process of passing mobile phase though a column.
V Columns are either open tubular or packed.

Accepted Answer

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

Question 9

The resolution between two peaks is defined as resolution =  .Which variable is INCORRECTLY defined?

Accepted Answer

A) tr is the retention time. 
B) Vr is the retention volume. 
C) wav is the average peak width measured at the base of each peak. 
D) w1/2av is the average peak width measured at the base of each peak,divided by 2. 
E) resolution is the separation between two adjacent peaks.

Question 10

The observed variance,  ,for a peak is the sum of the variances from all contributing factors.Which of the following is not a contributing factor to  ?

Accepted Answer

A)   
B)   
C)   
D)   
E)

Question 11

The partition coefficient is modified when the pH of the aqueous phase is adjusted or when a chelating agent is added.The partition coefficient is renamed the distribution coefficient.What is the impact on the extraction of a weak acid into an organic solvent as the pH of the aqueous phase increases?

Accepted Answer

A) As the pH increases the value of D decreases and the percentage weak acid left in the aqueous phase decreases. 
B) As the pH increases the value of D increases and the percentage weak acid left in the aqueous phase increases. 
C) As the pH increases,the value of D decreases and the percentage weak acid left in the aqueous phase decreases. 
D) As the pH increases the value of D increases and the percentage weak acid left in the aqueous phase decreases. 
E) As the pH increases the value of D decreases and the percentage weak acid left in the aqueous phase increases.

Question 12

Calculate the resolution for two chromatographic peaks that elute at t_r1 = 1770 s and t_r2 = 1800 s with base peak widths of w₁ = 51 s and w₂ = 57 s.

Accepted Answer

The answer of Calculate the resolution for two chromatographic peaks...

Question 13

Which is NOT true for solute retention?

Accepted Answer

A) Retention time,tr,is the elapsed time between injecting the sample to the arrival of a sample component at the detector minus the dwell time between the end of the column and the detector. 
B) Adjusted retention time is tr' = tr - tm,where tr is the retention time and tm is the time for mobile phase or unretained solutes to pass through the column. 
C) The relative retention,F1F1F1S1F1F1F10 =

,is the ratio for the adjusted retention time for two components of the sample,where tr2' > tr1' so that F1F1F1S1F1F1F10 > 1. 
D) The retention factor,k =

,is the time,tr,required to elute a component minus the time,tm,for mobile phase to pass through the column divided by tm. 
E) The relative retention,F1F1F1S1F1F1F10,also equals

,where K2 and K1 are the partition coefficients for components 2 and 1.

Question 14

Which is true for plate height?
I The smaller the plate height,the narrower the peaks.
II The larger the plate height,the better separation between peaks.
III Plate height can be calculated from the column length,L,and the number of theoretical plates,N.
IV For fixed number of theoretical plates,N,the longer a solute is on column,the wider the peak will become.

Accepted Answer

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

Question 15

A solute is to be extracted using 150 mL of solvent.Of the options below,which will extract the maximum amount of solute?

Accepted Answer

A) extract with 30 mL five times 
B) extract with 37.5 mL four times 
C) extract with 75 mL twice 
D) extract once with the entire volume 
E) extract with 50 mL three times

Question 16

Calculate the number of theoretical plates and plate height for a peak with a retention time of 1295 seconds,a width at the baseline of 27 seconds and elutes from a 15 m column.

Accepted Answer

The answer of Calculate the number of theoretical plates and...

Question 17

The relative retention between two solutes,1 and 2,is F1F1F1S1F1F1F10 = 1.35.If the adjusted retention time for solute 2 is 293 s,what is adjusted retention time for solute 1?

Accepted Answer

A) 396 s 
B) 217 s 
C) 189 s 
D) 241 s 
E) 344 s

Question 18

Suppose that the partition coefficient for an amine,B,is K = 3.0 and the acid dissociation constant for BH⁺ is K_a = 1.0 x 10⁻⁹.If 50.0 mL of 0.010 M aqueous amine is extracted with 100.0 mL of solvent two times,what percentage amine remains in aqueous solution if the pH of the aqueous phase is 9.00?

Accepted Answer

The answer of Suppose that the partition coefficient for an...

Question 19

Which is NOT true when scaling up preparative chromatography?

Accepted Answer

A) Keep column length constant. 
B) Cross-sectional area of a column is inversely proportional to the mass of analyte. 
C) Maintain constant linear velocity. 
D) Sample volume applied to column is proportional to mass of analyte. 
E) If you change column length,mass of sample can be increased in proportion to total length.

Question 20

The longer an analyte remains on the column,the broader the peak becomes.Peaks widen with time on column due to :

Accepted Answer

A) effusion. 
B) diffusion. 
C) adsorption. 
D) absorption. 
E) viscosity.

Exam 24: Introduction to Analytical Separations

____________________ is a plot of detector response versus retention time.

Which comparison of open tubular columns to packed columns is INCORRECT?

Calculate the weak acid,HA,concentration that remains in the aqueous phase when 50.0 mL of 0.184 M HA at pH = 4.75 is extracted with 50 mL of toluene three times.The partition coefficient for the extraction is 5.17,favoring toluene.The K_a for HA is 8.0 x 10⁻⁴.

____________________ is the physical transfer of solute from one phase to another.

For two separated solutes the  = 1.10 and the k₂ = 4.38.How many theoretical plates are required to achieve a resolution of 1.5?

The van Deemter equation describes plate height in terms of constants A,B,C,and the linear velocity,u_x.Which statement is NOT true for the van Deemter equation?

Which form of chromatography is INCORRECTLY defined?

The resolution between two peaks is defined as resolution = .Which variable is INCORRECTLY defined?

The observed variance, ,for a peak is the sum of the variances from all contributing factors.Which of the following is not a contributing factor to ?

Calculate the resolution for two chromatographic peaks that elute at t_r1 = 1770 s and t_r2 = 1800 s with base peak widths of w₁ = 51 s and w₂ = 57 s.

Which is NOT true for solute retention?

A solute is to be extracted using 150 mL of solvent.Of the options below,which will extract the maximum amount of solute?

Calculate the number of theoretical plates and plate height for a peak with a retention time of 1295 seconds,a width at the baseline of 27 seconds and elutes from a 15 m column.

The relative retention between two solutes,1 and 2,is  = 1.35.If the adjusted retention time for solute 2 is 293 s,what is adjusted retention time for solute 1?

Which is NOT true when scaling up preparative chromatography?

The longer an analyte remains on the column,the broader the peak becomes.Peaks widen with time on column due to :

Exam 24: Introduction to Analytical Separations

____________________ is a plot of detector response versus retention time.

Which comparison of open tubular columns to packed columns is INCORRECT?

Calculate the weak acid,HA,concentration that remains in the aqueous phase when 50.0 mL of 0.184 M HA at pH = 4.75 is extracted with 50 mL of toluene three times.The partition coefficient for the extraction is 5.17,favoring toluene.The Ka for HA is 8.0 x 10−4.

____________________ is the physical transfer of solute from one phase to another.

For two separated solutes the  = 1.10 and the k2 = 4.38.How many theoretical plates are required to achieve a resolution of 1.5?

The van Deemter equation describes plate height in terms of constants A,B,C,and the linear velocity,ux.Which statement is NOT true for the van Deemter equation?

Which form of chromatography is INCORRECTLY defined?

The resolution between two peaks is defined as resolution = .Which variable is INCORRECTLY defined?

The observed variance, ,for a peak is the sum of the variances from all contributing factors.Which of the following is not a contributing factor to ?

Calculate the resolution for two chromatographic peaks that elute at tr1 = 1770 s and tr2 = 1800 s with base peak widths of w1 = 51 s and w2 = 57 s.

Which is NOT true for solute retention?

A solute is to be extracted using 150 mL of solvent.Of the options below,which will extract the maximum amount of solute?

Calculate the number of theoretical plates and plate height for a peak with a retention time of 1295 seconds,a width at the baseline of 27 seconds and elutes from a 15 m column.

The relative retention between two solutes,1 and 2,is  = 1.35.If the adjusted retention time for solute 2 is 293 s,what is adjusted retention time for solute 1?

Which is NOT true when scaling up preparative chromatography?

The longer an analyte remains on the column,the broader the peak becomes.Peaks widen with time on column due to :

Calculate the weak acid,HA,concentration that remains in the aqueous phase when 50.0 mL of 0.184 M HA at pH = 4.75 is extracted with 50 mL of toluene three times.The partition coefficient for the extraction is 5.17,favoring toluene.The K_a for HA is 8.0 x 10⁻⁴.

For two separated solutes the  = 1.10 and the k₂ = 4.38.How many theoretical plates are required to achieve a resolution of 1.5?

The van Deemter equation describes plate height in terms of constants A,B,C,and the linear velocity,u_x.Which statement is NOT true for the van Deemter equation?

Calculate the resolution for two chromatographic peaks that elute at t_r1 = 1770 s and t_r2 = 1800 s with base peak widths of w₁ = 51 s and w₂ = 57 s.