Question

A polystyrene resin molecular exclusion HPLC column has a diameter of 7.8 mm and a length of 30 cm. The solid portions of the gel particles occupy 20% of the volume, the pores occupy 40%, and the volume between particles occupies 40%. (a) At what volume would totally excluded molecules be expected to emerge? (b) At what volume would the smallest molecules be expected? (c) A mixture of polyethylene glycols of various molecular masses is eluted between 23 and 27 ml. What does this imply about the retention mechanism for these solutes on the column?

Short answer

(a) The volume at which totally excluded molecules be expected to emerge is${\mathrm{V}}_{\mathrm{x}}=0.4\times 14.3\mathrm{mL}=5.7\mathrm{mL}$

(b) The volume at which the smallest molecules be expected is

${\mathrm{V}}_{\mathrm{y}}=0.8\times 14.3\mathrm{mL}=11.5\mathrm{mL}$.

(c) The solutes given in the task are adsorbed on the resin, if they weren’t they would be eluted at lower volumes.

Step-by-step solution

Define molecular exclusion:

Separation of chemical substances and particles by separate movements using a two-stage analytical system.

The volume at which totally excluded molecules be expected to emerge:

(a)

Here we will calculate the volume at which would the totally excluded molecules be expected to emerge.

Total volume of the column:

$$\begin{gathered} \mathrm{V}={\mathrm{\pi r}}^2\mathrm{l} \\ \mathrm{V}=\mathrm{\pi }{\left(0.39\mathrm{cm}\right)}^2\times 30\mathrm{cm} \\ \mathrm{V}=14.3{\mathrm{cm}}^3=14.3\mathrm{mL} \end{gathered}$$

Final volume:

Note that r=diameter /2 which is 7.8 mm/2= 39 mm.

The smallest molecules be expected:

(b)

Calculate the volume at which the smallest molecules would be expected:

${\mathrm{V}}_{\mathrm{y}}=0.8\times 14.3\mathrm{mL}=11.5\mathrm{mL}$

The retention mechanism for these solutes on the column:

(c)

Answer the question about the retention mechanism for solutes given in the task on the column:

Solutes given in the task are adsorbed on the resin, if they weren’t they would be eluted at lower volumes.