Question

A mixture of benzene, toluene, and methane was injected into a gas chromatograph. Methane gave a sharp spike at 42.0 s, whereas benzene required 251 s and toluene was eluted in 333 s. Find the adjusted retention time and retention factor for each solute, the relative retention, and the unadjusted relative retention. The question comes from "Quantitative Analysis" by Daniel Harris, and is from the ninth edition, in Ch. 23 (chromatography), but I can't find the answer or steps anywhere. Thanks.

Answer 1

Given: Methane gave a sharp spike in 42 s, benzene in 251 s and toluene was eluted in 333 s

The adjusted retention time = total time – Non retained component

The adjusted retention time for benzene = 251 s – 42 s = 209 s

The adjusted retention time for toluene = 333 s – 42 s = 291 s

The retention factor for each solute

Longer the component retain in column, the greater its retention factor

K = t_r –t₀/t₀

The retention factor for benzene = (251 s – 42 s)/42s = 5

The retention factor for toluene = (333 s – 42s)/ 42 s = 6.93

The relative retention factor is ratio of adjusted retention time for any two components

The relative retention α = tr2/tr1

α =291s/209s = 1.39