Question

Why is it important to maintain a constant flow rate for the carrier gas in a gas chromatography experiment?

Answer 1

Carrier gas is important in gas chromatography as it is used to move the vapourized solute through the column. We prefer an inert carrier gas such that it does not react with the stationary phase and instrumental components, especially at high temperatures.

Constant flow of carrier gas is needed to maintain good column efficiency and obtain reproducible elution times.    Linear velocity of the carrier gas can influence the overall time of analysis and efficiency of the seperations. The efficiency of the carrier gas is maximum at an optimum linear velocity.   Linear velocity is related to the retention time by the following equation:

t_r = L (k+1)/ µ

where, t = Retention time   L= Column length k = Retention factor µ = carrier gas linear velocity

Changes in viscosity of carrier gas is caused due to wide temperature programming range and the viscosity impacts the linear velocity. Constant flow rate maintains the optimum linear flow rate despite changes in gas viscosity for temperature controlled analyses. For this reason it is important to maintain a constant flow rate for the carrier gas in a gas chromatography experiment.