The best way to extend the life of a gas chromatography (GC) capillary column is to not foul it in the first place. It is important to pay close attention to sample preparation to remove as many nonvolatile or less-volatile matrix components as possible. The best way to prolong your gas chromatography column life is to use selective techniques such as QuEChERS (quick, easy, cheap, effective, rugged, and safe), dispersive solid-phase extraction (dSPE), or solid phase extraction (SPE).
- Avoid exposure to direct sunlight: Exposure to direct sunlight leads to stationary phase degradation due to UV catalyzed oxidation reaction is a UV-catalyzed reaction. For this reason GC capillary columns should be store in an enclosed space away from sunlight. When the columns for long term, the column column end caps should be used. It will ensure that oxygen will not get into the column. This practice will also reduce the time required for column conditioning.
- Column bakeout: The easiest way to reduce column contamination is to incorporate a short, high temperature bake out at the end of the you GC method. 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 a gradient or ballistic increase until the last components elute from the column.
- Column conditioning: When conditioning the GC column for GC analysis, allow the carrier gas to flow through the column at room temperature for 10–30 min (thicker phases and longer columns will need the full half hour) to remove dissolved oxygen before raising the oven temperature to 20 °C above the maximum method temperature, or to the isothermal or gradient temperature upper maximum limit of the column, whichever is lower. This approach will significantly reduce the time required to condition the phase at elevated temperature, which will be 1 h maximum. Overnight conditioning of modern capillary columns at high temperatures is unnecessary and simply wastes stationary phase.
- Proper column installation: Prevent the column from touching the oven walls on installation: to avoid the formation of “baked” (brittle) polyimide column coating, which, apart from being a hot spot within the column, can lead to column breakage over time.
- Use guard columns: The use of retention gaps (guard columns) is also very effective for protecting capillary columns from the deposition of involatile materials or the stripping of phase from the column inlet. Uncoated, deactivated silica capillaries with lengths of 0.5–3 m can be used to trap involatile material, and it is significantly less expensive to replace these guard columns than the analytical column itself. Some users are reticent to use guard columns because of the perceived difficulties with joining the guard column to the analytical column; however, the availability of low dead volume, low thermal mass unions means that this problem is no longer a valid concern.
- Use spitless injections with care: It should be noted that splitless injection will introduce more sample matrix onto the column, and the use of retention gaps with splitless methods for GC analysis should be seriously considered. It may also be useful to consider if a low split ratio may be used without compromising the sensitivity of the analytical method.
- Avoid certain solvents: Certain solvents such as acetonitrile and tetrahydrofuran can be particularly harmful to GC stationary phases, and these solvents (and even traces of them in your typical solvents or sample preparation eluates) should be avoided as stringently as possible. Similarly, acidic or basic solutions should be avoided where possible, especially where derivatization reactions or SPE mechanisms require a pH adjustment to optimize conversion or recovery. (Check the column compatibility before starting analysis).
- High capacity traps: The use of high-capacity traps (gas filters) in the GC system on the carrier gas line of your instrument will also greatly extend capillary column life. It is important to have both oxygen (activated alumina) and moisture traps in-line, which will prevent the chronic oxidation of the stationary phase over time. The use of self-indicating traps will help to remind you when the trap needs to be changed. The use of prepurged traps with snap-lock fittings will reduce the amount of air and moisture introduced during filter change.
- Consider trimming the column length: In the event that peak shape or efficiency deteriorate, remember that it is perfectly acceptable to trim the column at the inlet end to recover the column performance. It is often not necessary to remove much of the column to restore performance, and often it is possible to remove as little as 10–20 cm to fully restore the column to “good as new” standards. Where more of the column needs to removed, be aware that peak retention time may drift outside the retention time windows set in the acquisition method and that these windows may need to be adjusted to avoid missing peaks within the chromatogram.
Summary
Prevention is better than repair. A broken down gas chromatography capillary column results not only in lost time but could also necessitate repair work. To avoid these pitfalls, a GC scientist should use above maintenance and care steps to extend the life of a gas chromatography (GC) capillary column. It is also important to focus on sample preparation and remove nonvolatile or less-volatile matrix components. Selective techniques like QuEChERS, dispersive solid-phase extraction (dSPE), or solid phase extraction (SPE) should be employed for optimal care and maintenance of the GC column.Â