What is the maximum temperature of a GC capillary column and why is it important?

This post will briefly address this question and provide some general information and guidelines to help you better understand the significance of capillary GC columns maximum temperatures (“max temps”).

Capillary column manufacturers will typically use a combination of historical or statistical data and industry norms to determine realistic and optimal maximum operating temperatures for columns based on stationary phases and film thicknesses.

Metal capillary columns such as Restek’s MXTs can withstand (relatively) higher temperatures than most fused silica columns since they do not have polyimide on the outside (which can degrade at high temperatures).

In general, most polar columns will typically have relatively low “max temps” and are more easily damaged by higher temperatures. On the other hand, non-polar columns (such as polysiloxanes) are usually given higher maximum operating temperatures and tend to be more durable and rugged during higher temperature operation. What this usually means is that it is relatively easier to damage or kill a polar column by exceeding its max temp.

Why? Because stationary phases in these categories have different functionality, structures, and thermal stabilities.

By “tailoring” the max temp to both the phase and film thickness of a given column, manufacturers allow users to benefit from maximum column lifetime and analytical performance in the laboratory.

Let’s take a look at an example from our catalog:

As you can see, we specify two different maximum recommended operating temperatures for columns. First is the max isothermal operating temperature, which provides good thermal stability with minimal bleed generation. Second is the max programmed operating temperature, which is intended to be used sparingly and in short duration – for example, during column conditioning to remove contamination or to elute high molecular weight analytes which otherwise may not come off the column at lower temperatures.

Basically, max temp limits are designed to be a three-way compromise balancing column bleed, performance, and lifetime (i.e. – the lowest bleed with the best performance and longest lifetime).

What is column bleed? As described in one of my colleague’s posts, column bleed is essentially stationary phase degradation resulting from damage to the phase from sample matrix, oxidation, and/or exposure to relatively high operating temperatures. In the realm of chromatography, low bleed allows for the best signal to noise ratio between the peak and the baseline while high bleed from a degrading column masks signals (peaks) and makes peak identification and resolution efforts much more challenging.

Why is film thickness an important consideration? Thicker films have relatively higher bleed levels than thinner films (because there is more stationary phase coated onto the column).

So, what happens if I exceed these temperatures?

Taking a column above the recommended max isothermal operating temperature will result in baseline rise (more bleed) which may interfere with quantitation and resolution of components eluting during the bleed profile. Taking this one step further, exceeding the maximum programmed operating temperature, even briefly, accelerates wear and tear on the column and may shorten its operational lifetime, damage the phase, and contaminate your detector. Extended exposure to temperatures at or above the max temp overnight or over an entire weekend could potentially permanently cripple, damage, or kill a column.

Please be aware that air leaks are always dangerous to columns and when coupled with high temperature option, the combination of phase oxidation and high temperature can be quickly and absolutely fatal to the column. For these reasons, careful and thorough leak checking using a handheld electronic leak detector is highly recommended.

In summary, it is best to never exceed the manufacturer’s recommended max programmed operating temperature. Will doing so instantly “kill” the column? No, but pushing the temperature limits of a GC capillary column is not only extremely risky, but also very dangerous.

For other columns and phases, we’ll plan to revisit this topic in a future post.

Thanks for reading!