In a Gas Chromatograph, separation of different constituents of a sample occurs in the column. This makes the column a very important component in gas chromatography. GC columns are basically two types; the capillary column and the packed column.
Capillary columns are essentially made up of a thin fused-silica capillary and the stationary phase which is coated on the inner surface of the capillary, while packed columns are typically of glass or stainless steel coil that is filled with the stationary phase; the packing can as well be coated with the stationary phase.
Prolonged life and application success of columns can be achieved by proper column care and use. Columns care includes proper installation, choice of gas and, maintenance including storage and regeneration of performance, in some cases.
The care of a column should start from the point the column is being installed freshly. A new column is expected to be supplied with both ends covered with a septum or in some cases a metal cap. This is to prevent air or moisture from entering the column. If air enters the column, oxidation of the stationary phase may occur, thus damaging the column and reducing its life span.
1. Ensure that the septum have been removed from both ends
2. Trim a minimum of 2cm from both ends of the column and check that a clean square cut has been made.
3. Install the column nut into the column after which a ferule will be installed. . Install the inlet end of the column into the GC inlet, getting familiar with your GC’s injection type will be essential for the insertion dept of your column into the GC inlet. It is recommended that you refer to your instrument’s manual for correct insertion depth. Ensure that you do not over tighten the column nut, thereby breaking the ferrule and damaging the column.
4. Turn on the carrier gas to check if there is gas flow through the column. This can be done by dipping the detector end of the column inside a solvent, e.g. Methanol. There should be bubbles if there is gas flow through the column.
5. Install the detector end of the column into the detector as described in 1. Above. Refer to instrument’s manual for the correct insertion depth at the detector end.
6. Check for leaks using an electronic leak detector.
7. Allow the column to purge for some time to expel any oxygen that might have entered the column.
This is done in a case of column contamination or if the column is newly installed. This is usually done to achieve clean baseline.
To condition a column, the following steps may be followed:
1. Ensure that the system is leak free before going on with the conditioning
2. Heat the GC oven to a little below the column maximum temperature or a little above the method maximum, especially if the method maximum is far lower than the column maximum.
3. Stop the conditioning when the baseline is stable or clean.
1. Column Trimming: GC columns require regular maintenance to preserve optimum performance. Samples analyzed by GC often contain non-volatile material that becomes permanently retained by the column. Also some compounds can degrade the stationary phase. Both of these problems will be seen as deteriorating peak shapes, usually in the form of tailing peaks and unstable baselines. Fortunately the non volatile material and stationary phase damage mostly occurs at the inlet end of the column. To restore the performance of the column it is necessary to remove the damaged portion of the column; up to 1m of a 30m capillary column can be removed without a significant effect on the resolution of the column.
2. Leak Checks: A common source of column degradation comes from air leaks. This usually comes from leakages through the septum or from the gas regulator. If the system is not air tight, oxygen can be introduced into the column leading to the rapid degradation of the stationary phase
3. Good gas quality: Oxygen in the carrier gas also degrades the column. This is further accelerated at high temperatures and the damage is irreversible. To prevent this, gases of the best quality must be used; gas impurity filters should also be installed on the gas line.
Always remember to treat your column right so that it can give you good results…
For further reading, visit: http://www.labsphere.biz/pdf/consummables/gs-tek/GS-tek-column-care.pdf,
http://www.chemicool.com/definition/gas_chromatography_columns.html, https://tools.thermofisher.com/content/sfs/brochures/TN-GC-Column-Installation-Maintenance-TN20684_E.pdf and http://www.agilent.com/cs/library/eseminars/public/Installation%20Care%20and%20Maint%20GC%20Columns.pdf
Authored by: Ayodeji Ogunlowo; a Service Engineer at Applied Analytical Systems Litd., 8, Atunwa Street, Ikeja, Lagos, Nigeria. Phone (234) 802 2320 862, email: [email protected] website www.aasnig.com