Can Column Bleed also be a “Good” Thing?

2011-jaap-pasfoto4We see all kind of developments in GC technology to stabilize stationary phases and to make GC columns that bleed as low as possible.

A question I asked myself: Is it really always advantageous to have low bleed?

I sure understand that low bleed will get us highest signal-to-noise.  And if we combine that with inertness we get very good peak shape.  That’s why Restek developed the Rxi-series of columns, see http://www.restek.com/Landing-Pages/Content/gen_B003;

But is there also “an other story to tell”?

Yes, there is..  Bleed products will also have a deactivation effect.   That means that columns with high bleed, will produce a lot of degradation products. It was already published in 1978, where PEG degradation products were used to deactivate glass capillary columns, see

J. of Chrom. A, Volume 167, issue (December 21, 1978), p. 231-241. “Comparison of methods for the deactivation of glass open-tubular columns with PEG 20M”.

Bleed deac-1

Fig.1 Siloxanes will form cyclic break down products. The concentration depends on amount of stationary phase and temperature

Siloxane based stationary phases will also bleed and will form degradation products, typical cyclic siloxanes (fig.1).  These products will also act as deactivating agents, especially if the columns/surfaces are operated at higher temperatures. There are many publications on this.

Bleed deac-2

Fig. 2 Impact of bleed products on peak shape for sulfur compounds. A: original response; B: after conditioning. Sometimes a little bleed is helping the chromatography.

The result is that high-bleed systems will deactivate transfer lines, as well as electrodes in MS systems.  Sometimes columns are conditioned in a MS system at a higher temperature, just to generate bleed products that will minimize ionization source activity.

This also plays a role in sulfur-specific systems. Fig 2A shows a Sulfur Cheliminescence detector where sulfur peaks are tailing.  After conditioning with a “higher bleed” column, fig 2B, the sulfur peak shape improved.  Thanks to Jim Luong, Dow Canada, for sharing the data.

So sometimes a little bleed can be a good thing..

 

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