Gas chromatography Post _3 ( Flow control)
This is my 3rd post in GC. In fact, this topic which I am going to demonstrate in brief seems minor or not so important. However, I believe that is an important angle which a lot my ignore.
Flow control& The relation between pressure and flow rate are essential if you are looking for a perfect components separation, retention times, and identification. Now let us move to the topic:
1- The gas flow in the capillary column is small depending on the type of gas and diameter of
The column .it varies from 0.1 ml up to 10 ml per minute.
2- A well regulated and constant flow is important for the reliability, the accuracy and the
Reproducibility of retention values.
for a column diameter of 0.25mm : N2 flow is 0.40 ml/min, He is 0.7ml/min, and H2 1.1ml/min.
while for a packed column of 0.53mm diameter: N2 flow is 5.0 ml/min, He is 9.0ml/min, and H2 12.0 ml/min.
It is obvious that the flow is significantly varies based on column diameter and type as well. This means different separation quality, retention values, and …..
3- The relation between pressure and flow rate:
1-The flow rate is the amount of gas flowing through a column per unit time.
The amount depends on the gas velocity and the column diameter.
2- The pressure causes the gas to flow. Pressure and flow are related to each other
By the following equation: P= F*R
P= pressure R= resistance F= flow
Resistance is related to Column length, diameter, a viscosity of Carrier gas, temperature,
and external tubing
A pressure regulator is installed now to supply a constant gas pressure.