In Gas Chromatography, it is very important to protecting the column and instrument components from exposure to dirty samples. Non-volatile or high molecular weight components in the sample can contaminate the column and can cause poor peak resolution, lower accuracy, and reduce column lifetime. In addition, GC components such as the glass liners and seals in the GC inlet will be contaminated and may require frequent replacement.
Usually, cutting off the damaged portion will often restore your column’s performance, but over time performance will degrade to a point where the column can no longer be used. Discussed below are some simple ways to help protect your column and increase lifetime:
Ensure Proper Sample Preparation
Proper sample preparation is the first step in minimizing or eliminating contaminants and matrix effects, resulting in longer column lifetimes and increased signal-to-noise ratios. Depending on your analysis, choose a sample preparation technique that addresses the needs of your sample – there are several options, including sample filtration, and use of QuEChERS, and solid phase extraction. Sample Filtration: filter your samples using syringe filters prior to injection.
QuEChERS: for broad clean-ups of samples with varied functional groups, you may try the “Quick Easy Cheap Effective Rugged and Safe” method. This is more selective than syringe filters and well-suited for food matrices, but have been applied to other matrices. QuEChERS kits are available commercially, prepared for immediate use.
Solid Phase Extraction (SPE): You can also use SPE for clean-ups and to eliminate contaminants. SPE is the most selective option. SPE cartridges and kits are also available commercially, prepared for immediate use.
Use of Guard Columns
The use of guard columns helps to protect analytical columns from contamination and damage. Guard columns are relatively inexpensive are therefore more easily replaceable.
Traditional guard columns are 5 or 10meter pieces of deactivated tubing that are connected to an analytical column using a glass press-fit connector. The tubing acts like a trap for non-volatile residues that would otherwise damage the stationary phase of your analytical column. Traditional guard columns may be difficult to seal and can sometimes leak after normal column maintenance. There are also integrated guard columns that are built directly into an analytical column on one continuous length of tubing; these provide the same protection as traditional guard columns but also eliminate the possibility of leaks
Use A Glass Wool Liner
The liner is the first line of defence for your column and the type you choose can make a big difference in how much contamination gets onto the column. The easiest way is to add a small amount of silanized glass wool to a liner, which traps the non-volatile compounds and prevents them from entering the column. However, note that glass wool can also add activity for acids, bases, and pesticides. Crushing the glass wool can lead to increased activity, so it is recommended to purchase pre-packed liners, rather than try to pack your own.
“Baking Out” the Column
The easiest way to reduce column contamination is to add a short, high temperature bake out at the end of the standard GC method. This bake out helps remove high boiling contaminants that would otherwise remain in the column and cause damage. To bake out, the final oven temperature needs to be set high enough to ensure elution of these compounds, but not so high as to cause thermal damage. This can be done either isothermally, or more commonly via an oven ramp until the last components elute from the column.