Gas Chromatography

Question 1

What is the principle of gas chromatography (GC)?

Answer 1

GC separates volatile organic compounds using a gaseous mobile phase and a liquid stationary phase.

Question 2

What types of compounds can GC analyze?

Answer 2

GC is used for volatile and semi-volatile compounds with boiling points below 400°C.

Question 3

Why is GC primarily used in pharmaceutical analysis?

Answer 3

t is reliable and sensitive for identifying and quantifying volatile compounds, impurities, and residual solvents.

Question 4

What is the role of the carrier gas in GC?

Answer 4

It transports the sample through the column. Common carrier gases include helium, nitrogen, and hydrogen.

Question 5

What happens in the injection port of a GC system?

Answer 5

The sample is vaporized and introduced as a narrow plug of vapor into the column.

Question 6

What are the two types of columns used in GC?

Answer 6

Packed columns: Filled with solid particles coated with stationary phase.
Capillary (open tubular) columns: Thin stationary phase coating inside the column.

Question 7

How is column temperature controlled in GC?

Answer 7

A thermostatically controlled oven maintains the temperature, often increasing during separation for optimal resolution.

Question 8

What is the function of the flame ionization detector (FID)?

Answer 8

It detects organic compounds by ionizing them in a flame and measuring the resulting ion current.

Question 9

Why is the thermal conductivity detector (TCD) called a universal detector?

Answer 9

It detects all compounds that differ in thermal conductivity from the carrier gas.

Question 10

What is the advantage of using a mass spectrometry (MS) detector in GC?

Answer 10

MS provides molecular weight information and can identify components of incomplete separations.

Question 11

What factors influence retention time in GC?

Answer 11

Volatility (boiling point): Less volatile compounds are retained longer.
Polarity: Polar compounds interact more with polar stationary phases.

Question 12

Why is derivatization sometimes necessary in GC?

Answer 12

to increase volatility, improve chromatographic peak shape, or make thermally labile compounds stable.

Question 13

List three pharmaceutical applications of GC.

Answer 13

Residual solvent analysis.
Drug purity determination.
Detection of drugs of abuse.

Question 14

What are two major advantages of GC?

Answer 14

Fast analysis with high resolution.
Requires only small sample sizes (μL or μg).

Question 15

What are the main limitations of GC?

Answer 15

Limited to volatile compounds with boiling points below 400°C.
Not suitable for thermally labile or non-volatile compounds.

Question 16

Why must samples be soluble in GC?

Answer 16

Samples must not react with the GC column, and solubility ensures they vaporize properly.

Question 17

What is the main principle of gas chromatography (GC)?
A. Separation based on solubility in a liquid solvent.
B. Separation of volatile compounds using a gaseous mobile phase and liquid stationary phase.
C. Separation of non-volatile compounds using ion-exchange techniques.
D. Identification of compounds using UV absorption.

Answer 17

b

Question 18

Which of the following is the most commonly used carrier gas in GC due to its safety and wide velocity range?
A. Hydrogen
B. Helium
C. Argon
D. Oxygen

Answer 18

B

Question 19

In gas chromatography, what is the primary function of the injection port?
A. To detect analytes as they elute from the column.
B. To vaporize the sample and introduce it as a plug of vapor.
C. To separate the components of the sample based on boiling point.
D. To measure the thermal conductivity of the carrier gas.

Answer 19

B

Question 20

Which type of GC column offers higher resolution but lower sample capacity?
A. Packed column
B. Capillary (open tubular) column
C. Ion-exchange column
D. Gel filtration column

Answer 20

B

Question 21

What type of detector in GC is known for detecting organic compounds by ionizing them in a flame?
A. Thermal Conductivity Detector (TCD)
B. Refractive Index Detector (RID)
C. Mass Spectrometry Detector (MS)
D. Flame Ionization Detector (FID)

Answer 21

D

Question 22

Which of the following statements about derivatization in GC is TRUE?
A. It is used to make volatile compounds more polar.
B. It increases the volatility and stability of thermolabile compounds.
C. It decreases the chromatographic peak shape.
D. It reduces the sample’s interaction with the mobile phase.

Answer 22

B

Question 23

What determines the order of elution in gas chromatography?
A. Sample concentration only
B. The polarity and volatility of the analytes
C. The pressure of the carrier gas
D. The pH of the mobile phase

Answer 23

B

Question 24

Which of the following is NOT a limitation of gas chromatography?
A. Limited to volatile compounds with boiling points below 400°C.
B. Requires samples to be thermally stable.
C. Can analyze complex mixtures without a mass spectrometer.
D. Not suitable for large, non-volatile biomolecules.

Answer 24

C

Question 25

Which detector is often referred to as the “universal detector” in gas chromatography?
A. Flame Ionization Detector (FID)
B. Thermal Conductivity Detector (TCD)
C. Mass Spectrometry Detector (MS)
D. Nitrogen-Phosphorus Detector (NPD)

Answer 25

B

Question 26

What is the primary advantage of using a mass spectrometry detector (MS) in GC?
A. It is the cheapest detector available.
B. It identifies compounds by their molecular weight.
C. It has low sensitivity compared to other detectors.
D. It is only used for qualitative analysis.

Answer 26

B