Ghost Traps/Ghost Columns

[racheladele875]

I've seen some mention of the use of ghost traps or ghost columns to remove ghost solvent peaks from mobile phases. I've tried to find more information about the chemistry of how this would work, and what the "packing material" would be on something like this. All of the manufactures seem to use phrases like proprietary information. Any information would be helpful. Thanks!

[Rndirk]

I must admit I haven't come across the use of ghost traps/columns.

I suppose you could install some kind of filter upstream of the injection to purify the mobile phases. Degassing and filtering out particles is standard on HPLC systems, catching organic molecules is not as far i know.

These traps could be made of a variety of materials: polymers/membranes, activated carbon, microporous functionalized materials,...

Personally I would only use them as a last resort and stick to high purity, degassed water/organic solvents. I like to track down and eliminate contamination instead of masking it.

[Gerhard Kratz]

First off all, what ever is AFTER the injection system is part of the separation system and if validated method is used you cannot change things so easy. What ever is BEFORE the injection system you can do what ever you want.
Many years ago it was discussed to use a saturator column befor the injection system. That means it was used a guard column with C18 material and 10µm or larger particles. Glas beads with a layer of C18 modified silica were also used. Filtration was one aim, second was that if hydrolysis of the silica happens it will happen on the saturator column and the solved silica will have a protection affect on the analytical column. K.K. Unger published some papers on that and Uwe Neue mentioned that in his book on HPLC.

[EmpowersBane]

A common method to reduce ghost peaks in gradient methods is to fit a C8 packed column low diameter (Phenomonex do provide these) between the Aqueous Line A or B and the mixer via a short, 5-7cm stainless steel tube fitting. This can trap any contaminants before they accumulate at the head of the column. It needs to be conditioned or changed regularly though for best use.

[racheladele875]

Thank you all for taking the time to respond. Our lab currently has limited use of these on UPLC applications. We're already using high purity solvents, and filtering any aqueous based mobile phases before putting them on the system. I just wanted a better understanding of how the ghost columns were actually binding with materials and what it would be pulling out of the mobile phases.

I appreciate the help!

[EmpowersBane]

Trace contaminants in the aqueous mobile phase can become enriched on the head of the analytical column and then elute once the concentration of organic becomes sufficiently high. Even filtering the aqueous mobile phase/buffer will not remove these contaminants, depending on the source of the water.

A short C8 or C18 column between the pump and gradient mixer acts as a kind of additional filter or ghost peak trap, allowing only the highest quality of aqueous mobile phase to reach the column. It does not affect the selectivity of the sample but care should be taken that the length of the steel tubing between the pump and mixer is not too long as to add additional dwell volume to the system.

[HPLCaddict]

Most of the replies aimed at using a C18/C8 column for on-line purification of the mobile phase. But: this is only possible with high-pressure gradient (aka binary pump) systems. In quaternary systems this won't work, since if you include such a column after the mixer, the gradient will elute all the junk of this column once the organic content ist high enough - just as it does on the analytical column.
These ghost traps are something else - they actually can be used on quaternary systems to purify the eluents. So, they must be filled with a much stronger adsorbent than plain vanilla C18 silica. I've used one them occasionally and must they: it worked. Even with gradients rising to high organic contents, ghost peaks were practically eliminated. And while I basically agree that it's better to track down and eliminate any contaminants, this can be quite time consuming.
Drawback of these columns: Obviously, it's not possible to clean them, even with pure ACN. So, once they're exhausted, they must be thrown away. If using one, be careful about the contents of your mobile phase. Simple buffers are no problem, but if using ion-pairing reagents or any other additives, the ghost trap may actually trap these additives...
Concerning the original post: Unfortunately, I don't know what's inside these columns, and I guess the manufacturer won't tell.

[racheladele875]

THANK YOU! That's exactly what I was after!