Monolithic columns

[Alchemik]

Monolithic HPLC Columns: which brand better Onyx (Phenomenex) or Chromolith® (Merck)? Resolution of the separated compounds by Monolithic C18 (100 mm x 4.6) is comparable with traditional C18 columns with the length ........? Are welcome, comments, opinions and observations with the use of Monolithic columns, especially about improving separation between analysed compounds. Thank you!

[Jiri Urban]

Let me know if you have any question regarding (lab-made) polymer monoliths. I might help you. However I have limited knowledge about commercially available monolithic columns.

[tom jupille]

Jiri is being unduly modest.

Here is my (grossly oversimplified) take.

The Tanaka patents on silica-based monoliths were licensed to EM. My understanding (based on third-hand information, so I would not take an oath as to the veracity!) is that the Onyx columns were, at least initially, re-labelled Chromolith.

From what I have seen, the efficiency (plate height) of the silica-based monoliths is comparable to that of conventional packings in the 3 to 5 micron size range (but with the back pressure of a 10 to 15 micron packed column so that you can run at much higher flow rates).

As far as improving separation goes, resolution is impacted much more by selectivity (which is a function of column surface chemistry) than it is by efficiency. There are probably over 1,000 commercially available column packings versus a few tens of monoliths, but the overwhelming majority of separations can be done on phases which are available in both formats.

Jiri may want to comment further on this, but my feeling is that the appeal of monoliths is in capillary format which can be joined together to give very long columns. I can imagine something like a 1 meter column with something over 100,000 plates, at which point the peak capacity is high enough that you can work with relatively little selectivity, in effect making LC work a bit more like GC. But that's not where commercially available monoliths are at the moment!

[Jiri Urban]

Thank you Tom.

I agree with what you said.

I only hope that efficiency of (long) polymer monolithic columns will be soon higher than 100 000 plates (enough self-presentation;).

I see (polymer) monoliths in the future as supports/phases in miniaturized systems with integrated functions (sample preparation, separation, detection, ...). They can be prepared in any size and shape and you can tune their surface chemistry with almost any functionality.

It would be of course nice if they can reach currently available packed columns efficiency (sub 2um, core-shell). But for this we have to either wait or work harder;-)

[vladchern]

Let me know if you have any question regarding (lab-made) polymer monoliths. I might help you. However I have limited knowledge about commercially available monolithic columns.

I have an issue when analysing synthetic surfactants in the aqueous phase containing synthetic polymers (MW is up to few millions Daltons) used for enhanced oil recovery. Untreated polymer solutions create high back pressure especially in chromatographic columns. Most analysts treat such polymer containing samples with sodium hypochlorite (industrial bleach) before injecting into HPLC to destroy the polymers. However, the bleach can destroy surfactant molecules as well resulting in their wrong quantity measured.
So I have an idea to use the monolithic columns instead normal ones to avoid bleach excess usage and to save surfactants. I am just not sure if the monolithic columns will survive at the presence of synthetic polymers of MW=1,000,000.
As well as if I treated the solutions with some bleach, are the monolithic column packing material is stable against bleach components?
What about the stability (chemical as well) of the monolithic columns packing materials in comparison to normal columns?
Thank you.

[vladchern]

Let me know if you have any question regarding (lab-made) polymer monoliths. I might help you. However I have limited knowledge about commercially available monolithic columns.

I have got another question concerning making monolithic silica columns: what are the conditions they are prepared at? What I mean: I know that silica gel is packed in column, then treated at high temperature (which?) in some environment (alkaline?) to form bridge-like interconnections between silica particles.

Thank you.

[Jiri Urban]

As well as if I treated the solutions with some bleach, are the monolithic column packing material is stable against bleach components?
What about the stability (chemical as well) of the monolithic columns packing materials in comparison to normal columns?
Thank you.

I don't know, from my perspective I would say that stability of monolith to bleach wont be so great. On the other hand, monoliths are quite stable from chemical and thermal point of view (although (polymer monoliths) swell in organic solvents). And it might be problematic to use them at very high pressure.

[Jiri Urban]

I have got another question concerning making monolithic silica columns: what are the conditions they are prepared at? What I mean: I know that silica gel is packed in column, then treated at high temperature (which?) in some environment (alkaline?) to form bridge-like interconnections between silica particles.

Thank you.

I am not familiar with exact experimental conditions of silica monoliths preparation, however they are prepared by a sol-gel method, with hydrolysis and polycondensation reaction of silica precursors.

[tom jupille]

I know that silica gel is packed in column, then treated at high temperature (which?) in some environment (alkaline?) to form bridge-like interconnections between silica particles.

To expand a bit on Jiri's answer, no, that's not the way it's done. The silica is precipitated in situ.