Question

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R
Assertion A : In Gas-Liquid Chromatography (GLC) the Fatty Acid Methyl Esters (FAMEs) with long fatty acyl chains come out first from the column.
Reason R : Increased chain length of fatty acids leads to lower volatility and their increased retention on the GLC column.
In light of the above statements, choose the correct answer from the options given below

• A. Both A and R are true and R is the correct explanation of A
• B. Both A and R are true but R is NOT the correct explanation of A
• C. A is true but R is false
• D. A is false but R is true

Hint:

In Gas Chromatography, "lighter and more volatile" molecules always elute first because they spend more time in the gaseous mobile phase. Therefore, short-chain FAMEs elute before long-chain FAMEs.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Gas-Liquid Chromatography (GLC) is a powerful analytical technique used to separate and analyze volatile organic compounds, such as Fatty Acid Methyl Esters (FAMEs).
Separation in GLC is based on the differential partitioning of compounds between a mobile gas phase and a liquid stationary phase, which is heavily influenced by the volatility and boiling points of the analytes.

Step 2: Detailed Explanation:
Let us analyze both statements:
Assertion A Analysis: In GLC, the separation of FAMEs depends on their volatility.
Shorter-chain fatty acids have lower molecular weights, weaker van der Waals interactions, and higher volatility (lower boiling points).
Consequently, they partition more into the mobile gas phase and elute (come out of the column) first.
Longer-chain FAMEs are heavier, less volatile, interact more strongly with the stationary phase, and elute later.
Therefore, stating that long fatty acyl chains come out first is incorrect. Thus, Assertion A is false.
Reason R Analysis: As the carbon chain length of a fatty acid increases, its molecular weight and intermolecular forces (van der Waals interactions) increase.
This results in lower volatility and a higher boiling point.
In GLC, lower volatility means the compound spends more time dissolved in the liquid stationary phase rather than moving with the carrier gas, leading to an increased retention time on the column.
Therefore, Reason R is true.

Step 3: Final Answer:
Assertion A is false but Reason R is true, corresponding to option (D).