12 / 629
10
www.restek.comGC COLUMNS
Selecting a GC Column
Selecting a GC Column
Strategic column choices can improve lab productivity by assuring that speed and resolution are optimized.
While the number of choices available can be daunting, consideration of the resolution equation variables—
separation factor, retention (capacity) factor, and efficiency—simplifies the decision. Separation factor deter-
mines which stationary phase is most appropriate. Once the phase has been chosen, physical dimensions (in-
ner diameter, film thickness, length) can be selected based on retention factor and efficiency. Understanding
how separation factor, retention factor, and efficiency influence separations allows analysts to make effective,
informed choices and quickly select the best column for specific separations.
=
R N
1
4
k
k+1
α
-
1
X X
• Length
• Inner diameter
• Carrier gas type and
linear velocity
• Inner diameter
• Film thickness
• Temperature
N = L/H = Effective theoretical plate number
L = Column length
H = HETP = Height equivalent to a theoretical plate
k = Retention factor
α
= Separation factor
Baseline resolution (R = 1.5) is the goal.
• Stationary phase composition
• Temperature
A measure of
E ciency
.
This term is affected by:
A measure of
Retention
.
This term is affected by:
A measure of
Peak Separation
.
This term is affected by: