Question

An environmental chemist wants to use gas chromatography to measure the herbicide atrazine in water samples. This analysis is originally conducted on a 10-m long and 0.53-mm inner diameter open-tubular column that contains a 1.20-μm thick coating of a stationary phase, which gives a capacity factor of 10.5 for atrazine. The chemist later switches to another column of the same size and type that has a 2.65-μm thick coating of stationary phase. If all other conditions are kept the same, how much will the capacity factor for atrazine change between the old and new column? ​

Answer 1

ANS Capacity factor of old column = 10.5 for atrazine

as Capacity Factor (K') = (t_R - t_M)/t_M where t_R = Retention time which is directly proportional to the coating of a stationary phase and t_M is the universal measured of the retention in the chromatography

therefore, t_M = (t_R- t_M)/K' = (1.20 µm - t_M )/10.5 = 0.1142 - 0.0952 t_M (t_R = 1.20µm)

t_M (1+0.0952) = 0.1142,

t_M = 0.1042 µm

Now, New Capacity factor of column (K') = (t_R - t_M)/t_M

K' = (2.65 µm - 0.1042 µm)/0.1042µm ( New t_R = 2.65 µm)

K' = 24.43 (New column capacity factor for atrazine)

Difference Between the capacity factor of old and new column for atrazine will be (24.43 - 10.5 = 13.93) 13.93