Restek GC Column Selection Guide

Section III: Internal Diameter (ID)

When selecting an internal diameter, sample concentration and instrumentation must be considered. If the concentration of the sample exceeds the column's capacity, loss of resolution, poor reproducibility, and peak distortion will result. Table III (below) shows typical column characteristics. Note the limited capacity of narrow bore columns (0.18mm ID <50ng) versus the high capacity of 0.53mm ID columns (2000ng). Also, 0.53mm ID columns are recommended in high flow situations, such as with a purge and trap unit. Conversely, narrow bore columns can be installed directly into a MSD because of the limited flow at optimum linear velocity.

Table III: Typical column characteristics by ID

Select Column ID Make a Selection 0.10mm 0.18mm 0.25mm 0.28mm 0.32mm 0.45mm 0.53mm Column Parameters Values Typical Splitless Purge Time   He split vent flow rate (50:1 split ratio)   H2 split vent flow rate (50:1 split ratio)   Column OD (Ferrule ID)   Column Flow Rate (He @ 20cm/sec.)   Column Flow Rate (H2 @ 40cm/sec.)   Approximate Sample Capacity   Typical Effective Plates/m (80% CE)   Approximate column head pressure (He or H2 carrier gas) Column (m):                         Head Pressure (psig):                         Always optimize the column flow rate by using linear velocity.

other flow rates:

Septum Purge: 3-5cc/min.
Splitless Vent Flow: 50cc/min.
Direct Injection Flow Rate: 5-10cc/min.
Purge & Trap Flow Rate: 8-10cc/min.

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