Thermo Scientific ISQ, User Manual

Page: 28 / 152

2
Changing the Column
6 ISQ User Guide Thermo Scientific
• Internal Diameter —The smaller the diameter of the column, the better the separation.
However, smaller diameter columns do not have as much capacity for matrix or analytes.
As a result, smaller diameter columns are subject to overloading, which leads to retention
time shifts and peak shape changes. Larger diameter columns can accept larger
concentrations of material, but will require longer columns or slower GC oven
temperature ramps (which increases the analysis time) to match the separation power of
shorter columns. Typical column sizes for GC/MS have inside diameters (ID) of
0.25 mm. Smaller ID columns, such as the 0.15 and 0.10 mm, are becoming increasingly
popular. Additionally, 0.32 and 0.53 mm ID columns are commonly used.
• Film Thickness —With larger film thicknesses, there is more capacity for the analyte.
This capacity can aid in the separation of high concentration samples and in the
separation of very volatile samples because thicker stationary phases allow more
opportunities for the analytes to interact with the stationary phase. The optimal film
thickness depends on the internal diameter of the column and desired phase ratio.
Thick films with small internal diameters will give very strong interactions with the
analytes, which can result in longer analysis time and peak tailing. Large ID columns with
thin films will have very little interaction with the analytes, which will result in very fast
analysis times with little separation. Typical film thicknesses are 0.25 μm for a column
with an ID of 0.25 mm. Other common film thicknesses are 0.1, 0.5, and 1.0 μm.
• Length —The length of the column affects how much time the analyte has to interact
with the stationary phase. Longer columns typically have better resolutions and higher
capacities, but longer analysis times. Longer columns are also more expensive. Typical
column lengths are 15 or 30 meters for GC/MS, but 100 m columns may be needed for
very complex mixtures like gasoline. Very short columns (2.5, 5, and 10 m) are also
available.
Note Contact your local sales representative to order a Thermo Fisher Scientific column.
You can also refer to our catalog or visit our website at
www.thermoscientific.com/columns .