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GC COLUMNS
Selecting a GC Column
When selecting column ID, consider the type of injection, the detector being used,
and the concentration of sample (amount on-column). The injection technique is im-
portant because the column ID may need to be selected based on whether a split,
splitless, direct, cool on-column injection, or other sample transfer method is being
used. For example, 0.53 mm ID columns are ideal for cool on-column injections since
the syringe needle (26 gauge) will fit into the large column ID. In addition to column
ID, the detector and its flow requirements must be considered. For example, some MS
detectors can only operate under column flow rates of up to 1.5 mL/min; therefore, a
0.53 mm ID column, which requires higher flows for proper chromatography, is not
an option for MS work. Table II shows typical column characteristics for columns of
various inner diameters.
Film thickness has a direct effect on the retention and elution temperature for each
sample component. Extremely volatile compounds should be analyzed on thick film
columns to increase the time the compounds spend in the stationary phase, which
allows them to better separate. High molecular weight compounds must be analyzed
on thinner film columns. This reduces the length of time that the analytes stay in the
column and minimizes phase bleed at higher elution temperatures. Film thickness also
affects the amount of material that can be injected onto the column without overload-
ing it. A thicker film column can be used for higher concentration samples.
Table II: General Column Characteristics Based on ID
Column Inner Diameter (mm)
Characteristic 0.10 0.15 0.18 0.25 0.32 0.53
Nitrogen flow (mL/min) 0.2 0.3 0.3 0.4 0.6 0.9
Helium flow (mL/min) 0.6 0.8 1.0 1.4 1.8 3.0
Hydrogen flow (mL/min) 0.7 1.1 1.3 1.8 2.3 3.7
Sample loading capacity (ng) 2.5 10 20 50 125 500
Theoretical plates/meter 11,000 7,000 6,000 4,000 3,000 2,000
Note: Flows listed are for maximum efficiency. Sample loading capacities are estimates only. Actual sample
loading capacity varies with film thickness and analyte.
Fused Silica Capillary & PLOT Column
Ferrule Guide
GC Column ID Ferrule ID
0.15 mm 0.4
0.18 mm 0.4
0.25 mm 0.4
0.32 mm 0.5
0.53 mm 0.8
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