Does anyone have a description how to passivate a HPLC- stainless steel system? (Dionex-Summit)
All info is welcome. I had a corrosion problem due to HCl or NaOH application. Now can't get a proper baseline.
Thanks a lot!

For parts which are composed of stainless steel ONLY we use 30% HNO3 for about two hours. There was an interesting couple of articles on passivation some time ago in LC GC.

No amount of passivation will protect the stainless steel used in pumps from HCl. Don't use it.

I once checked with a corrosion scientist and found that the stainless steel used in Waters and Perkin Elmer (and probably everyone else's) pumps is not harmed by sodium hydroxide. I have used both these pumps with up to tenths molar concentrations of NaOH for several years with no harmful effect to the pump or anion exchange columns. Dionex perpetuates the myth that one needs a plastic pump to do anion exchange with NaOH and this is not correct.

When I answered this last night I was a bit drowsy, so that details were not given. Bill filled in nicely, I concur totally. Might as well deepen this some more while we are at it.
We have a pice of stainless tubing (partially polished to shininess) from our System which we use to test compatibility of mobile phases. HCL will blacken this quite fast (remember that reaction rate is also dependent on concentration). Basic mobile phases have never attacked it. Some people have mentioned that chloride ion from other sources than HCl will be harmful, even from trichloroacetic acid? Of course, any chloride ion below pH = 7 is H+CL- and/or H+ + Cl-. Next test is phosphate buffered saline at a pH of ~7.2. If it causes problems we will replace the NaCl with NaSCN which does not attack our stainless at "isotonic" concentration (0.15M).

Hans

I would not polish the tubing prior to testing. Polishing will remove the protective oxide layer and depending on what is used to polish could introduce exogenous iron. The goal of passivation is the removal of any exogenous iron via oxidation.

Unfortunately, type 316 stainless steel doesn't experience just one type of corrosion. There is chloride stress corrosion, pitting, crack and crevise corrosion, etc. Interstitial types of corrrosion will only be apparent under microscopic examination.

While it is clear that passivation with nitric acid will remove exogenous iron and prevent surface staining it is not so clear that it does anything to reduce steady state corrosion or the pitting types of corrosion.

If I had a problem with an HPLC that I thought was due to corrosion I would replumb the system with new prepassivated tubing and take appart and clean what I could. This is usually faster and more effective than passivation with nitric acid. Then as Bill said, don't use HCl, or high concentrations of NaCl or other solutions that attack stainless steel. Good luck.

Tom, you statet some of the reasons for why I polished PART of my 1/2" tube. The polished part is extremely sensitive to making any surface changes visible. Other parts are surfacs left from sawing, filing, and as delivered. I am not interested to see how passivated steel (of any type) reacts as I donīt know what the condition of my apparatus is on the inside at any given time. I want NO substance in there that may attack a weak part. Recently, there was no choice (time pressure) but to use PBS, I am just starting to test whether the relatively short exposures might have done some damage.
I have not seen any problems which could be ascribed to Fe ions, etc., so the testing method seems valuable (or all this business of using only PEEK or titanium surfaces is a lot of hype).

Hans

Here is a method I found on Waters Web site; it worked well for me.

bill


Passivation procedure for Waters Autosamplers

Created on: 06/08/95 Edited on: 03/18/97

Chemical safety procedures should be followed throughout this protocol. The
operator should read and be familiar with the MSDS sheets for each of the
reagents employed, should wear appropriate safety clothing -- eye glasses,
gloves, etc., and should ensure that the chromatograph is leak free prior
to beginning the passivation and cleaning. Proper disposal of the used
solvents is also essential.

The contaminants which are most likely to be found in a fluid pack are
residual cutting and machining oils associated with the drawing and
machining operations. These oils are not soluble in the passivation
solvents which are aqueous; consequently, simple passivation frequently
does not remove these oils, but it is quite immiscible with aqueous
solvents. Our recommendation is to flush the chromatograph of any buffer
with water, then with isopropanol and finally with methylene chloride.
Isopropanol is miscible with both water and methylene chloride and can
serve as a bridging solvent between the two. It is less hazardous than
tetrahydrofuran and easier to use.

Passivation of stainless steel with nitric acid removes 'scale' from the
internal surfaces and leaves the surface coated with an oxide layer which
resists further corrosion. When electrochemical detectors (including
amperometric, coulometric and conductivity detectors) are to be used with
liquid chromatographs it is essential to move labile transition metals from
the steel surfaces of the chromatograph. Many of the mobile phases used
with electrochemical detectors contain excellent chelating agents and an
aggressive treatment with strong chelating agents is recommended to remove
as much labile transition metal as is reasonably possible during the
passivation protocol. Phosphoric acid and EDTA at alkaline pH's (ca. pH 10)
are excellent choices for this treatment.

The cleaning and passivation procedure includes the following steps:

1. Ensure that the chromatograph is leak free.

2. Remove the column and detector(s) from the chromatograph.

3. Flush out any buffer from the chromatograph with filtered RO (or better)
water. (If the mobile phase is not miscible with water, it will be
necessary to use a bridging solvent.) The chromatograph should be
buffer-free and thoroughly flushed with water prior to beginning the
cleaning/passivation procedure.

4. Flush the chromatograph with isopropanol. Ensure that the WISP is well
purged with isopropanol. Pump about 100 mL of isopropanol through the
chromatograph.

5. Flush the chromatograph with methylene chloride. Ensure that the WISP is
well purged with methylene chloride. Pump about 100 mL of methylene
chloride through the chromatograph. Segregate the Methylene chloride waste;
chlorinated solvents require separate disposal.

6. Flush the chromatograph with isopropanol. Ensure that the WISP is well
purged with isopropanol. Pump about 100 mL of isopropanol through the
chromatograph. Note: the waste of this step will contain a residue of
methylene chloride and should be combined with the waste from step 5 for
proper disposal.

7. Flush the chromatograph with filtered RO (or better) water. Ensure that
the WISP is well purged with water. Pump about 100 mL of water through the
chromatograph.

8. Flush the chromatograph with 1:1 mixture of concentrated nitric acid and
water. Ensure that the WISP is well purged with the 1:1 mixture of
concentrated nitric acid and water. Pump about 100 mL of the concentrated
nitric acid and water through the chromatograph.

9. Flush the chromatogram with 2 Molar phosphoric acid.(prepared by
diluting 136 mL of concentrated phosphoric acid to a volume of 1 liter.
Note: Adding that concentrated phosphoric acid to 800 mL of water,
thoroughly mix, then dilute to volume). Ensure that the WISP is well purged
with the 2 Molar phosphoric acid. Pump about 100 mL of the 2 Molar
phosphoric acid solution through the chromatogram.

10. Flush the chromatogram with filtered RO (or better) water. Ensure that
the WISP is well purged with water. Pump about 100 mL of water through the
chromatograph. Continue flushing with water until the pH of the effluent is
neutral; pH test paper is adequate for measuring the acid content of the
effluent.

11. Flush the chromatograph with 0.002 Molar disodium EDTA dissolved in
0.01 Molar sodium hydroxide (prepared by dissolving 0.80 g of
ethylenediaminetetraacetic acid, disodium salt, dihydrate and 0.40 g of
sodium hydroxide in 1 liter of RO (or better) water and filtering the
resulting solution). Ensure that the WISP is well purged with the 0.002
Molar disodium EDTA solution. Pump about 100 mL of the 0.002 Molar disodium
EDTA solution through the chromatograph.

12. Flush the chromatograph with filtered RO (or better) water. Ensure that
the WISP is well purged with water. Pump about 100 mL of water through the
chromatograph. Continue flushing with water until the pH of the effluent is
neutral; pH test paper is adequate for measuring the base content of the
effluent.

13. Ensure that the waste from this procedure is properly disposed.

14. Return the chromatograph to the mobile phase. If necessary use a
bridging solvent to prevent miscibility problems. Ensure that the WISP is
well purged with the mobile phase and that the unit passes a
compressibility check. Install the column and detectors and equilibrate the
system.

Thank you all for the information you gave me; it has been very helpfull to me.It's good to know that HCl is the probably the trigger; I won't use it anymore.
Thanks for sharing your knowledge!