Organic Chemistry MCAT Practice Exam

What does gas chromatography primarily separate based on?

1. Concentration of the compounds

2. Boiling point of the compounds

3. Charge of the compounds

4. Molecular weight of the compounds

The correct answer is: Boiling point of the compounds

Gas chromatography primarily separates compounds based on their boiling points. In this method, a sample is injected into a column that is packed with a stationary phase. As the sample vaporizes and passes through the column, different compounds will interact with the stationary phase to varying degrees, which is influenced significantly by their boiling points. Compounds with lower boiling points tend to vaporize and elute faster through the column because they spend less time in the liquid stationary phase. Conversely, compounds with higher boiling points will condense more easily into the liquid phase, leading to longer retention times. This differential volatilization makes boiling point a key factor in the separation process. While concentration, charge, and molecular weight may influence how compounds behave in various chromatographic methods, they do not primarily dictate the separation in gas chromatography. The fundamental principle of this technique relies on the volatility of compounds, which directly relates to their boiling points.