FeCl3 in sample on XBridge and XTerra columns

[kerri]

Hi all. I am developing a quantitative method for an iron chelator by LC-UV and want to try out different conditions to maximize sensitivity. My boss said to try to exploit the chelating capabilities and add iron(III) to the sample matrix before injecting onto the column for separation.

My question is: do you think that this would be a safe idea on either the XBridge or XTerra families of columns? We are concerned about the iron coming into contact with residual OH groups (or others) and precipitating onto the column.

The final [iron] = 100nM (per sample).
mobile phase= 12% ACN, 10mM ammonium formate pH 8.5 (optimal conditions for analyte-iron interaction)
inj volume = 20uL

Thank You!!!

Kerri

[Uwe Neue]

If it does not precipitate in the mobile phase (which I do not expect to happen), it will not precipitate on the column either and will not create column clogging.

It is possible that iron will be adsorbed on residual silanol groups. However, this on itself is no worse than operating these columns on a stainless steel instrument: there is a slow accumulation of iron from the stainless steel in the instrument and/or brown solvent flasks. It is just happening more slowly during normal operation.

If the concern about this is tailing for analytes, the story is slightly different. Tailing on classical low-purity silicas is caused by metals inside the matrix, and not by metals on the surface of the packing.

[kerri]

Thank you, Dr. Neue!!!!

[Bruce Hamilton]

As Ferric Chloride solutions are commonly used to etch stainless steel for microscopic examinations, I'd be very reluctant to put it near any conventional stainless steel HPLC systems, even in sample solutions.

Bruce Hamilton

[HW Mueller]

Bruce, are these acidic FeCl3 solutions, and what are the concentrations used? I just wonder what the reaction would look like.

[Bruce Hamilton]

As far as I know, the solutions do not have acid added, although it may speed the process up.

Find a 316L SS sink or spatula and put some crystals of FeCl3 on it. Given the rather low ambient temps in your part of the world currently , you may have to warm it to the critical pitting temperature - which I think is about 16C. You will see the corrosion reveals the crystalline structure after about a quarter of an hour or so, perhaps quicker, perhaps longer, depending on the inherent stresses in the SS.

The mechanism will be corrosion texts, but I think preferential attack on austenite is the reason, and in ASTM G48 a 6% solution of ferric chloride ( no pH adjustment or acid added ) is used to test corrosion and welding heat-affected zones of SS at about 22C for a period of several hours to days.

[HW Mueller]

You really think this is relevant to the concentrations involved in doing the mentioned LC?

[Bruce Hamilton]

You really think this is relevant to the concentrations involved in doing the mentioned LC?

Yes. FeCl3 promotes intergranular corrosion on 300 series SS ( it's formed in trace amounts in some microbial attacks on SS ), and accelerates serious crevice/pitting. I wouldn't inject any into a SS system with those alloys, it probably would be worse than injecting HCl. However, it's not my system.

[Uwe Neue]

I wanted to stay out of this continued discussion, but decided against it.

Bruce, the idea was to use FeCl3 in a sample solution. The residence time of such a sample in frits or on any column or tubing segment is close to nothing, fractions of seconds, so I am not concerned about that at all.

Indeed, the sample will sit a bit longer in the injection loop, but if indeed the injection loop corrodes, it can be replaced easily. Plus. I doubt that it happens to any significant degree in the minute or so that the injection process might take.

It is good to be aware of the potential problem that you have pointed out, and Kerri can balance the benefits versus the potential issues. Anyway, I was not aware of such an issue with FeCl3, and I learned something. Thanks!

[kerri]

I really appreciate the responses to my question!! I learned a lot!!

I happened to catch a Modern Marvels episode about Acids on the history Channel a couple nights ago and ferric chloride etching was introduced. What timing!!!

Kerri