Ion-chrom: are PEEK pump componenets necessary?

[Andyp]

We are considering IC intrumentation options, and would like to know (from experienced users) if it is generally necessary to ensure a completely steel-free flow path (including pump parts)?

Does anyone use modular conductivity detection integrated into a standard LC system for IC? What are the drawbacks of this versus a dedicated IC system?

[Markus Laeubli, Metrohm]

Dear Andyp

It strongly depends on your application needs.
We started 20 years ago with an all stainless steel system running non-suppressed anions and cations without any problems. That first Metrohm IC (690 Ion Chromatograph) still works at some users places, now also equipped with chemical suppression.
One main limitation is Phosphate in low concentrations (µg/L). Phosphate will react with iron from not well maintained stainless steel surfaces.

PEEK systems require therefore less (preventive) maintenance. But most of the IC applications can be performed on stainless steel.

[HW Mueller]

Markus, are you referring to phosphate forming soluble complexes with Fe ions, or really to reactions with the iron metal?

Does anybody know whether phosphate buffers sweep out Fe ions in HPLC systems?

[Markus Laeubli, Metrohm]

Dear HW Mueller

I am refferring to "loosing" phosphate in the system. Spikes of low ppb levels phosphate give recoveries of < 100% while other ions work out well.
I assume that it is more a precipitation than dissolution effect. Therefore I also assume that a phosphate buffer does not dissolve iron from steel. I rather expect sort of a desactivation of ionic iron on the surface.

[Rafael Chust]

Some years ago I tested the same instrument in SS and PEEK version for IC and, to be sincere, there was no sensible difference...

Anyway, if you are looking for a dedicated IC instrument, just to avoid second thoughts when things go wrong, I would go for a PEEK system. If you are looking for an HPLC system to do IC too, then I would go for SS, as PEEK has some solvent restrictions.

Good luck!

[Andyp]

Hi Markus

Thanks for your comments.

We are concerned about the use of SS in IC from the point-of-view of corrosion in, for example, mineral acid mobile phases (?). Could you comment on this?

There is a strong chance that we would need to use IC for phosphate determinations, but at levels significantly higher than ppb (ppm or higher).

Thanks

[syx]

Sir, what about determination of biphosphonate class of drugs, which is known to be extremely difficult to analyze using liquid chromatography? Because they are very strong chelator, they readily interact with metals in HPLC systems (e.g., in injection valve or tubing or HPLC columns), giving rise to poor peak shape and irreproducible chromatography.
The journal said that ion-pair reverse phase liquid chromatography using a non metallic system is feasible for bisphosphonate determination. How could we get the condition?

Reference: Aluoch A et al. Stability Indicating Ion-Pair HPLC Method for the Determination of Risedronate in a Commercial Formulation. J. Liq. Cromatogr. Rel. Tech. 27(17): 2799-2813, 2004

[Kostas Petritis]

I would guess that passivation of the HPLC system before the analysis of these highly chleated analytes should work...

[Markus Laeubli, Metrohm]

Dear Andyp

IC eluent based on mineral acids are usually in the millimolar range and therefore will not give corrosion problems. Of course the system needs to be rinsed acid free when not used for a longer period.

Phosphate in ppm levels and higer work without any problem on SS. Kostas' remark about passivation is a key here. My experience: 0.2 mol/L nitric acid works well.

[syx]

I would guess that passivation of the HPLC system before the analysis of these highly chleated analytes should work...

Could you describe what shoud we do to passivate the system?

[HW Mueller]

The last of many?:
http://www.sepsci.com/chromforum/viewtopic.php?t=4222

If I wasn´t still on a "war footing" with the search system there would have been more, hope it works.

I checked last night on Fe ions and phophate. My old books don´t say much except that phophates and Fe+++ ions form soluble complexes, didn´t see anything on precipitates. Also, I have tested different phosphate buffers on stainless steel pieces and never have seen any signs of reactions, they didn´t even attack black oxides on the steel. So I wonder if anybody has some evidence for corrosion of any phophate species. Also, I still wonder whether phosphates sweep out iron ions from the HPLC system (via those complexes), so that mobile phases with phosphate buffers might be ideal for bisphosphonate HPLC?

[Mark Tracy]

See R.Tuytten, et.al, J. Chromatography A, 1104 (2006) 209-221. This discusses metal surfaces in the context of electrospray ionization sources, which in many ways is a worst-case situation, but they also have several references for the rest of the system.

Bisphosphonate drugs are very hard. Even when I ran them on a PEEK Dionex IC, I had trouble with metals. Finally, I just spiked the mobile phase with calcium and ran them as their calcium complexes.

For analyzing phosphopeptides on a SST system (after Ferric-IMAC enrichment), I started adding 0.5 mM Na4P2O7 to the mobile phase. That stopped the metals from smearing out some of the peaks. Of course, that made it incompatible with LC/MS, but I didn't care.

[Kostas Petritis]

A good way to passivate your system is by using 40 mM EDTA.2Na, overnight at low flow rates. Be careful to use the .2Na version of EDTA and not any other versions of it...

The 40 mM EDTA.2Na is a close to saturation solution. The advantage over HNO3 is that you can passivate all the components of an HPLC system, including the column if necessary...

[syx]

if we use HNO3 through the system with the column inside, is the acidity safe for the stationary phase?

[Kostas Petritis]

Of course not (at least not for any silica column)...

That was my point for using EDTA.2Na over HNO3...