Passage VI

Polarity is a measure of the separation of charge in a molecule. Molecules are attracted to other molecules based on polarity. In liquid column chromatography, a mixture is carried by the flow of solvent through a glass column containing an adsorbent material. If the components of the mixture have different polarities, they will interact differently with the solvent and adsorbent, causing the mixture to separate into its components. When the components elute (exit) from the column, they pass through a detector (see Figure 1).

The following experiments were done to study how using solvents and adsorbents of differing polarities affects the separation of a mixture. A component's elution time is the time it takes (from the start of the flow) for 100% of the component to be eluted. Table 1 shows the relative polarities (0 being nonpolar and 10 being extremely polar) of the components of the mixture and of the solvents used.

Experiment 1

A glass column 50 cm tall and 7 cm in diameter was packed with 3kg of a normal-phase (highly polar) adsorbent. A mixture containing 0.2 g each of Components A-D was dissolved and then added to the top layer of the adsorbent. Solvent I was then allowed to flow through the column at a constant rate. The % eluted of each component was measured for 50 min. The procedure was repeated using Solvents II and III (see Figure 2).

Experiment 2

Experiment 1 was repeated, but a reverse-phase (non- polar) adsorbent was used in each trial (see Figure 3).