Gas Chromatography (GC) Column Killers!

Our technical department is often involved in helping clients with “gas chromatography (GC) column autopsies.” Over the years, we have come to know the most common ways that you can effectively dispatch a column.

However, like anything related to health, there are cures and preventative measures that can help to revive an ailing column or avoid a premature demise. By following some simple guidelines, we can ensure your GC columns live a long and healthy life, and even when worrying signs appear, there may well be something we can offer to extend column lifetime and healthier-looking GC results.

Column Contamination

Stationary phase contaminants can be both semivolatile and nonvolatile, and these contaminants can arise from a variety of sources, including the sample matrix and anything that contacts the sample, such as vials, pipettes, and glassware. Contamination may also arise from the system itself, from released contamination from inlet septa, column ferrules, or gas traps (filters).

If column contamination is suspected, one can take several courses of action, including:

• Thermal bakeout at the isothermal maximum temperature of the column, for one to two hours. Any longer than this will render any non-volatile contaminants insoluble and will not be able to be rinsed from the column.
• Remove 0.5–1 m of stationary phase from the inlet end of the column and re-install.
• Solvent rinse the column. This is often a measure of last resort and manufacturers will all have their recommendations for this operation. Rinsing is often the most effective method for removing non-volatile residues.

Of course, expected column lifetimes based on contamination issues very much depend on the nature of your samples and the analytical method, but following the guidelines above will help to give your GC column the best fighting chance for a long and healthy life.

Thermal Damage

Thermal damage (degradation) of the stationary phase results in all the same symptoms of those mentioned above for oxygen damage. Fortunately, thermal damage occurs at a slower rate than oxygen damage because we can be sure there is no oxygen within the GC column. Usually, prolonged exposure of the GC column above the thermal limits is required to produce noticeable degradation.

If thermal damage is suspected, disconnect the column from the detector and heat at the isothermal temperature maximum overnight and trim 1–15 cm from the detector end of the column prior to re-installation. This may not restore the column to an “as-new” state, but it may buy you some time to order a replacement column without disrupting your analytical productivity!

Column Breakage

GC columns are coated with polyimide to give them thermal and mechanical stability, and these rarely spontaneously break within the GC column oven, with one notable exception. If the GC column is allowed to contact the walls of the GC oven, then the polyimide may “bake” at the contact spot and become more brittle than usual. When the GC oven fan activates, the resulting vibration of the column may cause the column itself to break.

In this regard, always make sure that the column is secure on its hangar and that the column is hanging clear of the side walls of the oven shroud. Also, make sure that the column leading from the inlet and to the detector is not touching the oven walls, is not longer than it needs to be, and is not user stress.

Column Cutting and Positioning

Although column cutting and positioning doesn’t really fit the criteria of “column killer,” they can certainly contribute to chromatographic problems. If the column is not cut using the correct technique, and it is cut at an angle or has rough shards, or is jagged on the end, peak splitting and tailing can result. If the column is not properly positioned in the inlet or detector outlet, then peak area response can reduce, and peaks will broaden. Therefore, instrument manufacturers’ guidelines must be closely followed to avoid these issues.

As you can see, there are many ways to damage and reduce the performance of your GC column. Many of the issues caused by column degradation are similar, often leading to confusion over the underlying cause and confounding our troubleshooting efforts. For this reason, it is imperative that we ensure proper preventative measures are in place. If issues do arise, then I hope this information will serve as a useful reference when troubleshooting and problem solving.

Tony Taylor is the Chief Science Officer of Element, EMEAA and the Technical Director of CHROMacademy. Direct correspondence to: LCGCedit@mmhgroup.com