Polymer columns

[rick1112]

I would like to know even with all the advantages with polymer columns why do users still prefer to use silica based columns?? Is there any major disadvantage with polymer columns??

Thanks

[shaun78]

There are selectivity differences between all columns, which can be a major (dis)advantage depending upon what you are trying to separate.

Silica columns will continue to be made on the sole reason of the number of BP/EP/JP/USP methods that use them alone...

[HW Mueller]

Resolution and pressure stability are generally higher with silica columns.

[tom jupille]

I'm a "Darwnian" in these matters: when a technology (or organism) is dominant, that usually means that it has features that are advantageous in its environment.

In the case of silica-based stationary phases these would have to include:
- rigid (no shrink/swell with solvent composition)
- robust (don't deform easily)
- relatively easy to control particle size, pore size, and their distributions during manufacture
- wide range of surface chemistries available (different bonded phases)

The disadvantages:
- for reversed-phase, a non-polar ligand must be attached to the surface
- limited pH range
- limited temperature range
- difficult to manufacture in high-purity

Could go either way:
- underivatized silanols affect selectivity


Micro-particle (10 micron and under) polymer-based stationary phases were actually in production at a time when the smallest silica-based materials were 37-44 microns. Almost no one today remembers automated amino acid analyzers! But, let's limit ourselves to reversed-phase materials. Advantages of polymer (usually macroporous polystyrene):
- wide pH range
- no bonded phase necessary for reversed-phase
- wide temperature range
- can be made from very pure starting material

Disadvantages:
- they do tend to shrink and swell a bit with organic solvent changes
- more difficult to control particle size range
- very difficult to control pore size and distribution
- more limited range of surface chemistry (hard to graft stuff to the surface one the polymer has been formed).

Could go either way:
- no silanols, so selectivity is different

[Bruce Hamilton]

Just one more opinion

Polymer columns tend to slightly depolymerise in some solvents/environments, resulting in unwanted minor peaks on common HPLC detectors.

It should be noted as a counter point, that polymer columns are unmatched for certain forms of high pressure chromatography - eg ionic ( Dionex, Aminex ), and size exclusion ( Jordi, Tosoh ).

Please keep having fun,

Bruce Hamilton

[ym3142]

my experience:

1, polymer column is much less robust, could die after not many injections, say, 20.
2, polymer column hates air so their instruction tell you how to avoid air when you install them;
3, a dry-or partially dry polymer column is irreversibly bad;
4, polymer column quality is less consistent from batch to batch;
5, some polymer columns have limit solvent compatibility.
6, polymer column does not like dramatic flow or solvent strength change;


7, Polymer column do provide some chromtograms no silica's can.

[rick1112]

Thanks to all of you for your reply

Just little curious, there are researches happening around about overcoming “disadvantagesâ€

[HW Mueller]

Bruce, depends again on what one is doing. For proteins the silica based SEC columns of Tosoh have the highest resolution.

[Uwe Neue]

The successful development of the hybrid columns (XTerra, XBridge) came exactly from the attempt to combine the advantages of silica-based columns with the advantages of polymer-based columns (more than a decade ago).

[ym3142]

I notice Rick mentioned

hydride silica columns

while Uwe Neue was talking about

the hybrid columns

. They were talking about different stuff. Thanks

[rhaefe]

Well I guess I have to add my $0.02:

In reading some replies here I have the suspicion some think that highly cross linked polymers and gel polymers (low cross linking) are pretty much the same. This is of course not true.
Lets look at highly cross linked polymers (polystyrene-co-divinylbenzene) like the PRP-1, PRP-h1, PLRP etc.
All those stationary phases are 55%XL or higher and are very pressure stable (350bar and sometimes more) and can handle pretty much any organic solvent used in LC. It is true that they do show some swelling indicated by a pressure increase when increasing the amount of organic solvent in a particular mobile phase or during a gradient run but that is really a non-issue. In addition, the swelling can be minimized by using adequate polymerization and cleaning procedures for the polymer. This will also take care of the "bleeding" of polymeric stationary phases Bruce mentioned. This bleed is usually only observed in LC-MS and not in LC-UV.
No special care has to be taken to avoid exposure of the packed column to air. I have left columns sit around without column plugs for days and they still performed according to spec (this is not a recommendation to do so...).
Lifetime is also not an issue as long as the same care is taken as someone would use with silica based columns (no particulates, use of guard columns or suitable sample prep prior to analysis etc). I have seen polymer columns which only failed after 15000 runs at 50 to 80°C and using high ionic strength mobile phases.

Gel or low cross linked polymers (10%XL and lower) are a completely different beast. They are used for carbohydrate analysis (HC-75, Aminex 87H, Carbosep, Coregel) or amino acid analysis (Aminosep etc). These columns are very sensitive to mechanical stress or exposure to some organic solvents or mobile phases. Pressure limits are around 60 to 70bar and it is very easy to over pressure them thereby permanently damaging the column.

To sum things up highly cross linked reversed phase columns based on polymeric stationary phases have two main advantages over silica based materials: pH stability (pH=1-13) and temperature stability (ambient to 225°C for PRP-1).
The biggest disadvantage is the lower column efficiency (lower plate count) when compared to silica based RP columns.

[Bruce Hamilton]

Well I guess I have to add my $0.02:

In reading some replies here I have the suspicion some think that highly cross linked polymers and gel polymers (low cross linking) are pretty much the same. This is of course not true.

Hi Robert,

Thanks for that excellent explanation - worth far more than $0.02.

Guilty as charged. I didn't distinguish between the normal and gel types, as I assumed that silica-based gel columns to have similar adverse pressure properties as 'eqivalent" polymer-based gel columns.

Thanks for the detailed responce pointing out the effect of cross linking, and the robustness of highly-cross-linked polymer columns. Good stuff to learn, as I was aware the 8 in Aminex-87H stood for the amount of cross-linking, but didn't know the significance.

Hans,

Thanks for the correction about columns used for proteins, other than eating proteins, I seldom work on them.

Please keep having fun,

Bruce Hamilton

[Uwe Neue]

to YM 3142:

I responded to the quest for info on polymer columns, and I was not talking about hydride column (which have no advantage that I can see).

I wanted to talk about inorganic-organic hybrid packings. The hybrid packings were created exactly based on the observation that polymeric packings have some advantages and some disadvantages, and that silica-based columns also have advantages and disadvantages. The idea was to attempt to create packings that combine the advantages of both worlds. The major advantages of silica-based packings are the hardness (can be used way beyond UPLC pressures), and the excellent mass transfer. The weakness of silica is the instability in the alkaline pH range. The major advantage of a polymer packing such as a styrene-divinylbenzene packing is is its pH stability. The disadvantages of all polymeric packings are the lower mechanical stability, swelling and shrinking, and the inferior mass transfer in the analysis of small molecules. Progress has been made in all aspects, but still there remains a big gap between the overall abilities of a polymer-based packing and silica or hybrid-based packings.

Today, the best hybrid packing (XBridge C18) can be comfortably used at pH 10, and is stable at room temperature even to pH 12. Otherwise it is a superb C18 packing, competitive with any modern silica-based C18.

[rick1112]

rhaefe worte

The biggest disadvantage is the lower column efficiency (lower plate count) when compared to silica based RP columns

what would be reason for the lower column efficency in polymer based column??

[rhaefe]

The main reason for the lower efficiency is the restricted mass transfer of analyte between the mobile and stationary phase.
This is inherent to conventional polymer phases and leads to peak broadening and tailing. It is mainly observed in small molecules, not in large ones like bio-polymers (nucleic acids, peptides and proteins).
Peak broadening and tailing can be minimized by using higher separation temperatures. The mass transfer kinetics are accelerated, mobile phase viscosities drop and band spreading/tailing decreases accordingly.