Chromatography Forum

Hey Folks

Forgive me if this has already been kicked around (I did a quick search and didn't see it).

Has anyone found that when using a hybrid column (X-bridge C18, just as a random example) that they get more retention of analytes than would be the case with the corresponding column on conventional C18.

Any feedback on that......or just in general, experiences with Hybrid columns as compared to conventional silica based columns would be of interest.

Thanks!

C18 is never the same!!!!! Surface chemistry of different brands is always different to others. To compare please check the table of hydrophobicity from different manufacturers. Particle size and pore size distribution of the stationary phase plays a role, the treatment of the stationary phase before bonding a silane on the surface, the kind of silane used for the bonding etc.! Many factors are involved to create the separation power of a stationary phase, silica or hybrid based.

This is one of the database of columns and how they are similar/different from each other.

http://www.usp.org/app/USPNF/columns.html

The selectivity of C18 columns will propably stay the same when you change to various manufactures. But the retention time and parametrs describing peaks will for sure be different.

How about if I shift the question a bit, and ask "what kind of performance have people been observing with hybrid columns".

Same as conventional (silica based columns)........different........more tailing........less tailing.......

Whatever you may have observed, and wish to share

Tailing has more to do with column loading and solvation power (prep solvent vs mobile phase).

If you're seeing excessive tailing, you ought to try to make your samples in your mobile phase (if possible, and you aren't already) or reduce your analyte concentrations. Sometimes saltier MP buffers can help, but that should be a last resort.

A story for caution: I had to chastise a fellow method developer for using 50 and 100mM potassium phosphate test MP solutions on an Agilent 1290. It cost my group a set of pump seals when one of the inexperienced analysts changed the instrument over to a different method, and didn't the developer didn't flush the instrument properly when he was done.

It has already been pointed out that it's not trivial to "compare" columns - and in this special case (hybrid vs. conventional silica) it's especially dangerous, because it's hard to judge it differences in chromatography are due to the underlying matrix (i.e. hybrid vs. conventional silica) or the bonded phase.

So much for the disclaimer - I've used several hybrid-based columns, namely Phenomenex Gemini and Gemini NX, Waters XBridge and YMC Triart. Generally speaking I've found them to be absolutely comparable to "equivalent" conventional-silica C18 columns in terms of efficiency (aka plate count) and peak shape. "Equivalent" in this context meaning hydrophobic, well-endcapped type-B silica columns, let's say something like a Phenomenex Luna, Waters Sunfire, Supelco Ascentis, YMC PackPro or similar. Selectivities (aka peak order) usually are also quite similar - meaning peak order usually is the same, but retention times may differ considerably - and of course an occasional shift of peak order is possible.

If, on the other hand, you compare these hybrid columns to other types of C18s, namely more polar ones like "old" type-A columns, polar-embedded columns or other stuff, you might see huge differences - just like Gerhard keeps on saying "C18 is never the same!"

@HippyLabRat: There used to be a time when peak-tailing was mainly caused by the column itself - namely basic analytes on type-A-silica columns. And these times are not over, as these columns are still widely in use.

Good Afternoon,

Nope, it's not trivial to compare HPLC columns; that said, here's a website that may help along those lines.

http://www.hplccolumns.org/database/compare.php

Looks like Dr. Stoll has more than a few Hybrid Stationary Phases in the database.

Happy Separations!