Chromatography Forum

I've re-plumbed an HPLC system using PEEK where possible, passivated the rest of the system with HNO3. I'm concerned that endogenous/exogenous Fe+++ is fouling the column and distorting peak shapes (this is especially noticeable for NO3-).

Can anyone recommend a "guard column," perhaps one that will chelate Fe+++, that I can put upstream the anion exchange analytical column?

In an earlier life (early 80s) I did a lot of "single column" IC (no suppressor) in all SS systems with no particular problems for nitrate. Those were fairly low-pH eluants (usually in the 3-5 range), but I wonder if stainless steel is really the root of your problem.

Primesep 100 guard should trap trivalent iron almost permanently.

Dear DJ

As Tom I did quite some non-suppressed IC on stainless steel equipment. Also I did not see Fe problems. We actuall used same pH range but also pH 7.5...9.0.
The only part which could cause problems was a steel eluent filter (not really stainless). Here we used fluorocarbpolymer instead.

In an earlier life (early 80s) I did a lot of "single column" IC (no suppressor) in all SS systems with no particular problems for nitrate. Those were fairly low-pH eluants (usually in the 3-5 range), but I wonder if stainless steel is really the root of your problem.

So then are you in the camp that believes Ion chromatography systems (dionex) composed entirely of titanium and or PEEk are unnecessary?

For most applications, yes. For example, I went back through my old files and dug up this chromatogram (circa 1983; probably actually run by Dave Togami when we were at Wescan):

Dear tom

I absolutely agree with your statement. Also we solved hundreds of applications non-suppressed on SS systems (good old times of the 690 Ion Chromatograph).

DJ,
I would not recommend to run fluoride determinations by IC on a titanium system.

How frequently do you passivate your SS system?

Fe+++ "strongly adsorbs to PS-DVB SAX"

Is this only in the presence of Cl-? (HCl always used in studies on anion exchange resin binding by Fe+++).

The guy previously had tried separation of common anions in 4 mM p-hydroxy benzoic acid. THe chromatograms looked awful, and Nitrate was not found. Once 0.1 mM NaSCN was added to the mobile phase, everything seemed to work magically. Nobody (NOBODY) uses this additive, so I was curious to try and understand how it helped. Turns out, -SCN is reagent for colorometric determination of Fe+++. I postulated -SCN was masking and or removing endogenous as well as exogenous Fe+++.

I passivated the system, and put a WCX guard up-stream my PS-DVB SAX analytical, and poof! Separation of all common anions without -SCN additive.

I'm curious, if for the moment we assume the Fe+++ was somehow causing secondary interaction, do you suppose it is "endogenous' (leached from stainless steel parts, or, exogenous (present in mobile phase. If the latter, this has to originate from impurities in the buffer, as I can't imagine the apparatus that generates 18 mega ohm holy water could let slip past a little iron with is subsequently captured on the WCX guard.

Any thoughts here?

Your speculation makes sense, but I can't offer any insight from experience. All the anion work we did at Wescan was on silica-based packings.

Dear DJ

I have seen similar effects on a polymer-based column as well. We actually used a Metrosep RP 2 Guard column. This kept the iron back. I assume that under the slightly alkaline pH, iron is already in the insoluble hydroxide form.

The iron traces may come from samples, but also from chemicals the eluent is prepared of. I assume that this effect has much more influence than the steel capillaries.

We passivated our SS systems once or max. twice a year.