Question 1

Which of the following best explains why high-performance liquid chromatography (HPLC) provides better separation of compounds compared to traditional column chromatography?

Accepted Answer

HPLC uses smaller particle sizes and high pressure, resulting in more frequent adsorption and desorption events.

Question 2

In gas chromatography (GC), which property of the sample is most critical for successful analysis?

Accepted Answer

The sample must be able to be vaporized without decomposition.

Question 3

A scientist is analyzing the presence of pesticides in food using HPLC. Which part of the chromatogram is used to determine the concentration of a pesticide?

Accepted Answer

The area under the pesticide peak.

Question 4

Why is nitrogen commonly used as the carrier gas in gas chromatography?

Accepted Answer

Nitrogen is unreactive and does not interfere with the sample analysis.

Question 5

A mixture is analyzed by HPLC and produces three peaks at retention times of 2.1 min, 4.5 min, and 7.2 min. If a reference sample of caffeine has a retention time of 4.5 min, which peak corresponds to caffeine?

Accepted Answer

The peak at 4.5 min.

Question 6

Which of the following is a major application of HPLC in the pharmaceutical industry?

Accepted Answer

Quantifying drugs in blood samples.

Question 7

In GC, what is the role of the stationary phase?

Accepted Answer

It provides a surface for sample components to adsorb and separate based on their interactions.

Question 8

A chromatogram shows a peak with an absorbance of 106 units for a caffeine sample. If the standard curve for caffeine is given by $A = 0.4C$ (where $A$ is absorbance and $C$ is concentration in ppm), what is the concentration of caffeine in the sample?

Accepted Answer

$C = \frac{106}{0.4} = 265$ ppm

Question 9

Which statement best describes the process of qualitative analysis in chromatography?

Accepted Answer

It involves comparing the retention time of a sample to known standards to identify compounds.

Question 10

In HPLC, why is the solvent pumped through the column under high pressure?

Accepted Answer

To overcome the resistance caused by the small particle size of the stationary phase.

Question 11

Which of the following would NOT be a suitable sample for analysis by gas chromatography?

Accepted Answer

A protein with a molecular mass of 50,000.

Question 12

A chromatogram is produced by passing a UV light through the eluent. What does the detector measure?

Accepted Answer

The amount of light absorbed by the eluent.

Question 13

Which factor would most likely increase the resolution between two closely eluting peaks in HPLC?

Accepted Answer

Decreasing the flow rate of the mobile phase.

Question 14

In a GC experiment, which compound will elute first from the column?

Accepted Answer

The compound that interacts least with the stationary phase.

Question 15

A technician needs to determine the concentration of a contaminant in drinking water using HPLC. Which procedure should they follow?

Accepted Answer

Measure the area under the contaminant peak and compare it to a standard curve.

Question 16

Which of the following is a limitation of gas chromatography?

Accepted Answer

It is limited to components that can be vaporized without decomposition.

Question 17

A sample is injected into a GC and passes through a column packed with alumina. What is the primary function of the alumina?

Accepted Answer

To serve as the stationary phase and adsorb sample components.

Question 18

Which of the following best describes the use of a standard curve in HPLC quantitative analysis?

Accepted Answer

It is used to determine the concentration of a compound by comparing peak areas to known standards.

Question 19

If a sample contains two compounds with similar retention times in HPLC, which adjustment would most likely improve their separation?

Accepted Answer

Decrease the particle size of the stationary phase.

Chromatography: Principles, Techniques, and Applications

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