In chromatography, which compounds are detected first?

In chromatography, the compounds that are detected first are those with the lowest affinity for the stationary phase of the chromatography system. This principle is central to the separation process in chromatography, as different compounds interact with the stationary phase with varying degrees of strength.

When a mixture of compounds is introduced into the chromatography system, those with lower affinity for the stationary phase will move more freely and quickly through the system, meaning they will elute (or exit) the column first. In contrast, compounds with a higher affinity for the stationary phase will interact more strongly and therefore take longer to move through the system, resulting in later detection.

Additionally, the characteristics of polarity can play a role, especially in certain types of chromatography, such as reverse-phase chromatography where less polar compounds tend to elute first. However, the key factor remains the affinity of the compounds for the stationary phase, which governs the order in which they are detected.

In summary, the lowest affinity compounds are detected first in chromatography due to their reduced interaction with the stationary phase, leading to a faster elution from the system.