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Exam 27: Chromatographic Methods and Capillary Electrophoresis

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Question 1

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What impact does the pH of the mobile phase have on the ability of a strongly acidic exchanger to interact with ions?

A) decreases the ability to interact with ions as pH decreases
B) increases the ability to interact with ions as pH increases
C) has no impact on the ability to interact with ions
D) decreases the ability to interact with ions as pH increases
E) increases the ability to interact with ions as pH decreases

F) A) and E)
G) C) and D)

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Question 2

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Which statement is NOT true for hydrophobic interaction chromatography?

A) Hydrophobic interaction chromatography has a hydrophobic stationary phase,which repels water and is not wetted by water.The technique is used primarily for protein purification.
B) Proteins are salted out of solution with ammonium,sodium,and potassium salts of phosphate and sulfate.Thiocyanate,iodide,and perchlorate salts increase the solubility of proteins in water.
C) The proteins are eluted from the column with a gradient of increasing salt concentration,increasing the solubility of proteins in water.
D) The most common stationary phase is an agarose gel with hydrophobic phenyl or alkyl groups attached and a pore size large enough to accommodate proteins.
E) A protein sample with a large concentration of ammonium sulfate is applied to the column.The ammonium sulfate causes the protein to stick to the hydrophobic surface of the stationary phase.

F) B) and E)
G) B) and C)

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Question 3

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Which is NOT a detector used with capillary electrophoresis?

Which statements are true for electroosmotic velocity? I Electroosmotic velocity,u_eo,is calculated experimentally using the retention time of a neutral molecule and the length of the column from the injector to the detector. II Electroosmotic velocity,u_eo,is the product of the electroosmotic mobility,_eo,and the electric field,E. III Electroosmotic velocity,u_eo,is inversely proportional to electric field strength,E. IV Electroosmotic velocity is equal to the electroosmotic flow.

Capillary columns require conditioning prior to their first use.Typical conditioning is washing with 1 M NaOH for 1 hour,followed by 1 hour of water,then 1 hour of 6 M HCl,and finally 1 hour of run buffer.Which statements are INCORRECT? I The NaOH wash is thought to generate the Si-OH groups on the silica surface. II The NaOH wash removes any acidic contaminants from the silica surface. III The HCl wash is thought to generate the Si-OH groups on the silica surface. IV The HCl wash removes metal ions from the capillary surface.

____________________ is used to isolate a single compound or class of compounds from a complex mixture by passing the sample through a column where only one solute is bound.The remaining solutes pass through the column.The bound solute is eluted from the column by changing a condition such as________________________________________ to weaken its binding.

Under what conditions will anions be detected at the cathode during capillary electrophoresis?

____________________ are instruments constructed on plastic or glass chips which use electroosmotic flow or pressure to move liquids through micrometer channels from one reaction site to another.

Sodium cation was separated from a mixture of cations via capillary electrophoresis,with negative detection.The instrument is equipped with a capillary 50 cm in length,with 45 cm to the detector.The separation took place under 30 kV with the neutral marker reaching the detector after 200 seconds.The retention time for Na⁺ is 85 seconds.Calculate the number of theoretical plates for the Na⁺ peak.The diffusion coefficient for Na⁺ in water is 1.0 × 10⁻⁹ m²/s.

________________________________________occurs when an electric field is applied to a capillary that has an electric double layer at the negatively charged surface inside the capillary.

X⁻,Y⁻,and Z⁻ are separated with an anion exchange column with a mobile phase containing A⁻.The strength,which the anions bind to the column,is Y⁻ > X⁻ > Z⁻ > A⁻.To elute the anions,the concentration of A⁻ is____________________ ,with____________________ eluting first,____________________ eluting second,and____________________ eluting last.

Capillary electrophoresis separates two analytes with retention times of 112 s and 113 s with a 60 cm capillary,with the detector 50 cm from the inlet.The voltage applied across the capillary is 20 kV.Assuming that the peaks eluted close enough that N is essentially constant,what is the resolution for the two peaks if N = 500 000 plates?

The commonly used detector with ion chromatography is the:

A sample of NaNO₃ and K₂SO₄ is separated on a suppressed-ion anion chromatography column.________________________________________is retained and separated on the separator column.________________________________________is used to elute the analyte from the separator column.____________________ is removed in the suppressor to reduce____________________ and allow for detection of analyte.

Which statement regarding capillary electrophoresis sample injection is INCORRECT?

The retention time for an analyte separated via capillary electrophoresis is 115 s.The separation occurred with a 50-cm column,with the detector at 45 cm,and a potential of 30 kV.A neutral molecule took 200 s to reach the detector.What is the electrophoretic mobility for the analyte?