How to choose Gas Chromatography Column?

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How to choose Gas Chromatography Column?
Before you start separating the complex compounds
of your mixture through chromatography, the most
important decision is to choose the right
column. Without the right column, you are not
going to get the correct results. There are some
criteria on which the selection of the right Gas
Chromatography Column depends. I will be trying
to discuss briefly each of the four criteria. So
lets start with what are the four criteria on
which the selection of a proper chromatography
column depends.
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1. Stationary Phase 2. Column Length 3. Column
I.D. 4. Film Thickness Stationary Phase This is
the most important in deciding the type of column
you need for your gas chromatography process. It
decides the ability and selectivity of the column
to separate the components of the mixture into
individual components. So what is a stationary
phase? A stationary phase is a layer or film
which is coated or chemically bonded on the inner
wall of any capillary column. Selecting a
stationary phase is important because it decides
the interactions between the organic compound
injected and the stationary phase.
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This means that the stronger the interaction
between the analyte and the phase, the longer
time the analyte is retained inside the
capillary. While the other compounds which do not
form strong bonds with the stationary phase go
outside sooner. The time of retention of the
mobile phase inside the column is the measure of
the phase-analyte interaction. There are wide
variations in the capillary column phases. This
is because, for each type of chemical property of
the stationary phase, the relationship of the
analyte-phase reaction differs. It may not be
possible to have the same reading for a
particular combination of analyte and stationary
phases. Column Length Usually longer the Flame
Photometric Detector for GC length, the more is
the efficiency or resolution is improvised many
times. But the disadvantage is that it increases
the backpressure. It is not that doubling the
column length will double the resolution.
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You can resolve for short columns if you do not
require a great resolution for separating the
components of a sample. However, decreasing the
column id along with a decrease in length can
improvise the resolution of screening along with
the short length of the column. Film
Thickness If you go for decreasing the thickness
of the film then you will get sharper peaks and
reduced column bleeds. But the disadvantage will
be that you have to increase the operating
temperature, decreased analyte capacity, and more
interaction between the analyte and the
stationary phase. On the other hand, the
increasing film thickness will help in increasing
the analyte capacity and lesser analyte
interactions with the stationary phase. But you
will also observe increased peak widths which
mean reduced resolution and more often column
bleeds and decreases in optimum temperature.
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Column I.D. gThe ideal I.D. depends on the
analyte you choose to separate. Column internal
diameters maintain a balance between sample
capacity or the amount of sample required for
sharp edge and efficiency or the number of
theoretical plates used.
SOURCE
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