Organic Chemistry MCAT Practice Exam

Which of the following best describes the mobile phase in chromatography?

1. It supports the mixture and retains compounds

2. It carries the mixture while traveling

3. It defines the separation strategy used

4. It determines the optical rotation

The correct answer is: It carries the mixture while traveling

In chromatography, the mobile phase plays a pivotal role in the separation process. Its primary function is to carry the mixture of compounds being analyzed as they move through the stationary phase. This movement facilitates the interactions between the compounds and the stationary phase, leading to their separation based on differences in their affinities for the stationary phase versus the mobile phase. The mobile phase can be a liquid or a gas, depending on the type of chromatography being employed (e.g., liquid chromatography or gas chromatography). As it flows through the stationary phase, the compounds in the mixture are transported at different rates, which results in their separation. The efficiency and effectiveness of the chromatography process heavily depend on how the mobile phase interacts with the compounds. In contrast, the other choices highlight concepts that do not accurately describe the role of the mobile phase. While supporting the mixture (as mentioned in one option) might occur due to the stationary phase, it is not the direct function of the mobile phase. Likewise, while the separation strategy can be influenced by the nature of the mobile phase (in terms of choice of solvents, for example), it is not exclusively defined by it. Optical rotation pertains to the optical activity of compounds and is generally not a function of the mobile phase in chromatography. Thus