GC Column Maintenance: Tips for Extending GC Column Life

July 1, 2018
Dawn Wallace Watson

LCGC North America

Volume 36, Issue 7
Page Number: 482

To extend the life of your GC columns, follow these best practices.

Like most things in chromatography, the best way to extend the life of columns is to not foul them 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 (GC) 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).

GC columns should be stored out of direct sunlight, and column end caps should always be used. Stationary-phase degradation (oxidation) is a UV-catalyzed reaction, and storing them in a dark cupboard or within the column box is highly recommended. Further, the use of column end caps will ensure that oxygen will not ingress into the column during long-term storage; this practice will also reduce the time required for column conditioning.

When conditioning the GC column, 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. It is good practice to keep 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.

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.

It should be noted that splitless injection will introduce more sample matrix onto the column, and the use of retention gaps with splitless methods 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.

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.

The use of high-capacity traps (gas filters) 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.

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.