Find the retention factors for octane and nonane in figure 23-7. What you measure distances , estimate them to the nearest 0.1mm.

(b) Find the ratio$\frac{\mathbf{t}\mathbf{i}\mathbf{m}\mathbf{e}\mathbf{}\mathbf{o}\mathbf{c}\mathbf{t}\mathbf{a}\mathbf{n}\mathbf{e}\mathbf{}\mathbf{s}\mathbf{p}\mathbf{e}\mathbf{n}\mathbf{d}\mathbf{s}\mathbf{}\mathbf{i}\mathbf{n}\mathbf{}\mathbf{s}\mathbf{t}\mathbf{a}\mathbf{t}\mathbf{i}\mathbf{o}\mathbf{n}\mathbf{a}\mathbf{r}\mathbf{y}\mathbf{}\mathbf{p}\mathbf{h}\mathbf{a}\mathbf{s}\mathbf{e}}{\mathbf{t}\mathbf{o}\mathbf{a}\mathbf{t}\mathbf{l}\mathbf{}\mathbf{t}\mathbf{i}\mathbf{m}\mathbf{e}\mathbf{}\mathbf{o}\mathbf{c}\mathbf{t}\mathbf{a}\mathbf{n}\mathbf{e}\mathbf{}\mathbf{s}\mathbf{p}\mathbf{e}\mathbf{n}\mathbf{d}\mathbf{s}\mathbf{}\mathbf{o}\mathbf{n}\mathbf{}\mathbf{c}\mathbf{o}\mathbf{l}\mathbf{u}\mathbf{m}\mathbf{n}}$

(c) Find the Relative retention for octane and nonane.

(d) Find the partition coefficient for Octane by assuming that the volume of the stationary phase equals half the volume of the mobile phase.

Finding the value of retention factor :

(a) Relative distance measure from figure 23-7 :

$t_m=10.4$mm,$t_r=39.8$mm for octane ,$t_r=76.0$ mm for nonane.

(You will have different measures depending on the size in your book)

Retention factor for octane,=$k_1=\frac{t_r}{t_m}=\frac{39.8}{10.4}=3.83$

Retention factor for nonane,=$k_2=\frac{t_r}{t_m}=\frac{76}{10.4}=7.31$

(b) $k=\frac{t_s}{t_m}$where $t_{s}and{t}_m$are the time spends in stationary and mobile phase.

Total time Octane spends on column ,$t=t_s+t_m=t_s+\frac{t_s}{k}=t_s\left(\frac{k}{k+1}\right)$

∴$\frac{t_s}{t}=\frac{k}{k+1}=\frac{3.83}{3.83+1}=0.793$

(c) Relative retention factor,_{$a=\frac{t_r\left(oc\tan e\right)}{t_r\left(nonane\right)}=\frac{76}{39.8}=1.91$}

(d) $k=K\times \frac{V_S}{V_m}$Or, $K=k\times \frac{V_S}{V_m}$Where k= Retention factor, K= Partition coefficient,

=Volume of the stationary phase, =Volume of mobile phase.

Given , $V_S=\frac{1}{2}{V}_m,\frac{V_m}{V_S}=\frac{V_m}{{\displaystyle \frac{1}{2}}{V}_m}=2$ ∴ $k=3.83\times 2=7.66$

Hence (a) Retention factor for octane and nonane are 3.83 and 7.31 respectively.

(b) Ratio = 0.793

(c) Relative retention for octane and nonane is 1.91

(d) Partition coefficient for octane , K = 7.66