Chromatography Forum

Has anybody got an opinion on whether it would be better to get an inline (directlyconnected) guard cartridge or a stand-alone guard column holder for a microbore 5um supelco C-18 column?

We are buying a new column, and as the old one let us down before without a guard column, we were looking into buying one of these, but werent sure if it would be better to get a direct or a stand alone guard column.... any ideas or opinions?

thanks for your help!
chel

For the direct-connect types, you need to make sure that the fittings are compatible between the guard and analytical columns. Third-party devices may not fit well enough. If your column vendor offers a compatible direct-connect guard, go for it.

If you asked me this question 10 years ago (or before) I would recommend "classical# guard-columns.

Since then, cartridge kits has become quite reliable, simple to use and cheap.

Besides other companies, Phenomenex has a system called SecurityGuard that you might check at www.phenomenex.com that proved to be very good.

While there are many different types of guard columns in the world, I do not think that the design of a guard column is very important. I am a strong advocate for the use of a guard column, and all my experience tells me that the best guard columns are prepared from the identical packing as the packing in the main column. That does not mean, that it should be a C18, if you are using a Symmetry C18 as the main column. It means that you will be best served, if you are using a Symmetry C18 guard column in front of a Symmetry C18 analytical column. Otherwise, you often run into unnecessary peak distortions and related problems.

I initially had really good experiences with guard columns.

Then changed batches on the next order of the same column. I wasted a lot of time testing the guard columns to see which were good and which were bad.

I was finding the use of the guard column compromised my separations. I talked to the manufacturer and they said they couldn't really afford to test guard columns like they tested columns due to price restrictions. They indicated that they did confirm that the guard columns had the same backpressure when packing.

Thus, I quit using them. I was doing protein precipitated plasma samples and could get 500-700 injections on a column. I just changed the prefilter every 1-200 samples. Often the column could be regenerated by reversing the flow and washing with various solvents.

I was wasting too much time worrying about saving the column. Found better just to buy a new one when needed..

I've only tried one type of precolumn from one manufacturer. Maybe others are much better.,

Cartridge-type guard columns would be my first choice. Easy to replace, and as good as the conventional guard columns.

Uwe is right though - you'll get best results if the guard column packing is the same chemistry -and brand- as the main column.

Sailor, interesting info on guards....at those prices charged for them!

These small empty columns by Upchurch (2x20mm, 2x10mm, etc.), which can be dry filled easily worked quite fine, even with a void in front (usually happened when 200bar mp hit the stuff, sometimes I just topped them off). One had to change these a little more often, costs pennies, though, including the time.... The trouble is that it´s continually more difficult to get stat. phase, especially in small amounts. I mentioned this caution before: Some body fluid samples are so cruddy that a guard doesn´t do much good (for instance, if one injection is sufficient to plug everything), one sometimes just has to do a better job of pre-cleaning.

(Also on this matter of time, regarding repairing or junking columns: Often one sees the operator sit around, bored, between injections, etc., etc....... the time could be used for repair.)