Chromatography Forum

Probably, there is already a topic discussing the pros and cons of monolithic columns implementation in comparison to regular silica columns, however I was not able to find such a topic (search tool did not provide any results).
My question is about replacing regular silica columns for RP HPLC with more advanced monolithic silica columns, which provide lower backpressure, higher peak resolution and longer lifetime. Since I have no experience in implementation of monolithic columns, but as everybody I am experiencing back pressure issues each time while using HPLC columns, I am very interested in whether anybody can share his/her personal experience about the matter:
a) what about compatibility with HPLC systems and detectors (e.g. ELSD)?
b) are there any tricks when using a monolithic column?
c) how to chose a monolithic column to replace a regular one?
d) which column producer have you already tried?
etc.

Thank you.

Lower pressure: definitely
Longer lifetime: quite possibly
Higher resolution: probably not

The advantage of commercially available monolithic columns is that the macropores (through which the bulk solvent flows) represent a much larger fraction of the cross-section than do the between-particle spaces in a conventional column. That means you have much less flow resistance (hence lower pressure for a given flow rate). In practice, this translates to a higher flow rate for a given pressure, which provides faster analysis.

If the column lifetime is limited by blockage from particulate contamination or precipitated sample, then the monolith will probably last longer (again, the macropores are bigger than the between-particle spaces, so less likely to plug). If the lifetime is limited by chemical deterioration of the stationary phase, or adsorption of sample components, then the monoliths and the packed columns won't differ much.

Large macropores mean long diffusion path lengths, and so monoliths tend not to be as good as the best small-particle packed columns. On the other hand, the low flow resistance means you can couple columns in series to get some of the efficiency back. To grossly oversimplify, you get the efficiency of a 3 to 5 micron packed column with the back pressure of a 10 to 15 micron column.

There's no fundamental incompatibility with current detectors, but they do tend to get noisier at higher flow rates. ELSD, in particular may have some issues, depending on how hard you push.

Tricks? No, they hook up pretty much the same way.

How to replace a conventional column with a monolith? You pretty much have to redevelop the method, but that's can be true of any column substitution. There's no guarantee that you're going to get the same selectivity.

Lower pressure: definitely
If the column lifetime is limited by blockage from particulate contamination or precipitated sample, then the monolith will probably last longer (again, the macropores are bigger than the between-particle spaces, so less likely to plug). On the other hand, the low flow resistance means you can couple columns in series to get some of the efficiency back. To grossly oversimplify, you get the efficiency of a 3 to 5 micron packed column with the back pressure of a 10 to 15 micron column.

It is a good idea to couple the columns. I tried to do that with regular columns, but the issue is increased backpressure in comparison with a single column.
Since I deal with samples coming from oil recovery coreflooding, I have always some dirty staff in each sample: asphaltenes, synthetic polymers of MW=1,000,000. Of course, I am interested to avoid blocking the column with those things.

What is the alkaline/acidic stability of monolithic column? Is it the same pH=2...8?
How are their thermo-stability: up to 60 or 90 C?

What is the alkaline/acidic stability of monolithic column? Is it the same pH=2...8?
How are their thermo-stability: up to 60 or 90 C?

pH stability of (polymer) monoliths is somewhere around 2 - 10 (polymer detachment from capillary is a bigger problem at pH 10)

and (again polymer) monoliths are stable up to ~300 °C, so working somewhere around 100 °C shouldn't be problem

For the silica monoliths, about the same as silica packings (about 2.5 - .

and (again polymer) monoliths are stable up to ~300 °C, so working somewhere around 100 °C shouldn't be problem

That's well into GC temperatures ! Has anyone ever tried a capillary polymer monolith in a GC ?

Peter

That's well into GC temperatures ! Has anyone ever tried a capillary polymer monolith in a GC ?

There are some papers, would you like me to find/send them to you?

EDIT:

Less common applications of monoliths III. Gas chromatography, J. Chromatogr. A 1184 (2008) 281 - 295.
http://www.sciencedirect.com/science/ar ... 7307012137

Little bit older, but good starting point.

Thanks Jiri

I ran search and had a quick look at a few of the papers. The applications are focussed on smaller molecules than I work with. There might be an application in purge and trap sampling if the polymers are stable to air and moisture from the samples.

Peter

IMO - air should not be a problem, and I believe that moisture too, but in that case I am not so sure.