Chapter 23, Problem 23.CE

(a)

Interpretation Introduction

Interpretation:

The retention factor for octane and nonane has to be calculated.

Concept introduction:

Retention factor:

The retention factor $\left(\text{k}\right)$ is given by

$\begin{array}{l}\text{k}\text{=}\frac{{\text{t}}_{\text{r}}\text{-}{\text{t}}_{\text{m}}}{{\text{t}}_{\text{m}}}\\ \text{Where,}\\ \text{k}\text{-}\text{retention}\text{factor}\\ {\text{t}}_{\text{r}}\text{-}\text{time}\text{required}\text{to}\text{elute}\text{the}\text{peak}\\ {\text{t}}_{\text{m}}\text{-}\text{time}\text{required}\text{for}\text{mobile}\text{phase}\text{to}\text{pass}\text{through}\text{the}\text{column}\text{.}\end{array}$

(b)

Interpretation Introduction

Interpretation:

The ratio between time octane spends in stationary phase and total time octane spends on column has to be calculated.

(c)

Interpretation Introduction

Interpretation:

The relative retention for octane and nonane has to be calculated.

Concept introduction:

Relative retention:

The ratio of the adjusted retention time of two components is given by relative retention $\text{α}$

$\begin{array}{l}\text{α}\text{=}\frac{{\text{t}}_{\text{r}}^{\text{'}}{}_{\text{2}}}{{\text{t}}_{\text{r}}^{\text{'}}{}_{\text{1}}}\\ \text{Where,}\\ \text{α}\text{-}\text{relative}\text{retention}\left(\text{also}\text{called}\text{separation}\text{factor}\right)\\ {\text{t}}_{\text{r}}^{\text{'}}{}_{\text{2}}\text{-}\text{adjusted}\text{retention}\text{time}\text{of}\text{component}\text{2}\\ {\text{t}}_{\text{r}}^{\text{'}}{}_{\text{1}}\text{-}\text{adjusted}\text{retention}\text{time}\text{of}\text{component}\text{1}\\ \text{The}\text{separation}\text{between}\text{the}\text{two}\text{component}\text{will}\text{be}\text{higher}\text{when}{\text{t}}_{\text{r}}^{\text{'}}{}_{\text{2}}\text{>}{\text{t}}_{\text{r}}^{\text{'}}{}_{\text{1}}\text{,}\text{so}\text{α}\text{>}\text{1}\end{array}$

(d)

Interpretation Introduction

Interpretation:

The value of partition coefficient for octane calculated.

Concept introduction:

Partition coefficient:

Partition of a solute is depends on “like dissolves like” concept.  This means the solubility of solute is more in a solvent whose polarity is similar to that of the solute.

The partition coefficient of solute $\left(\text{S}\right)$ is given by

$\text{Solute}\left(\text{in}\text{phase}\text{1}\right)\stackrel{}{\rightleftharpoons }\text{Solute}\left(\text{in}\text{phase}\text{2}\right)$

$\begin{array}{l}\text{K=}\frac{{\text{A}}_{{\text{S}}_{\text{2}}}}{{\text{A}}_{{\text{S}}_{\text{1}}}}\approx \frac{{\left[\text{S}\right]}_{\text{2}}}{{\left[\text{S}\right]}_{\text{1}}}\\ \text{where,}\\ \text{K}\text{-}\text{partition}\text{coefficient}\\ {\text{A}}_{{\text{S}}_{\text{1}}}\text{-}\text{Activity}\text{of}\text{solute}\text{in}\text{phase}\text{1}\\ {\text{A}}_{{\text{S}}_{\text{2}}}\text{-}\text{Activity}\text{of}\text{solute}\text{in}\text{phase}\text{2}\\ {\left[\text{S}\right]}_{\text{1}}\text{-}\text{Concentration}\text{of}\text{solute}\text{in}\text{phase}\text{1}\\ {\left[\text{S}\right]}_{\text{2}}\text{-}\text{Concentration}\text{of}\text{solute}\text{in}\text{phase}\text{2}\end{array}$