91Ó°ÊÓ

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

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

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

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