Question

Order the following compounds in order of elution in gas chromatography. Explain your reasoning.

conditions: Mobile Phase – Air (Flow Rate = 25 mL/min), Stationary Phase –poly(dimethylsiloxane),Oven Temperature – 110 ^oC.

1-pentanol, 2-hexanol, 2-pentanone, pentane

b) How would a gradient elution (55 ^oC – 120 ^oC) impact the chromatogram?

Answer 1

​If a component having a low boiling point than it will spend more time in the gas phase. Hence, its retention time will be less than a compound with a higher boiling point. ​

Therefore, compound with lower boiling point will elute first along with mobile phase i.e. Air

The boiling point for these compounds are (taken from google search):

1-pentanol (138 ^oC)

2-hexanol (140 ^oC)

2-Pentanone (101 ^oC)

Pentane (36.1 ^oC)

Hence, Order of elution of these compounds can be given as follow:

1) Pentane 2) 2-Pentanone 3) 1-Pentanol 4) 2-Hexanol

Pentane will elute first followed by 2-pentanone, 1-pentanol and at the last 2-Hexanol will elute.