Re: Potential leachables from 316L Stainless Steel

From: Muhammar (muhammar_at_hotmail.com)
Date: 08/21/04 

Date: 21 Aug 2004 16:57:51 -0700

First, I am not protein chemist so my comments are not that qualified.

I don't think you would get much metal salts leaching from stainless
steel at pH=3. I have seen corrosion/metal leaching from stainless
steel with aqueous hydrochloric acid, but the acidity was extremely
high in those cases (2-4M HCl, over several hours).

You can always do the acid wash as suggested before - but I would fist
do alkaline wash to remove grease then do acidic wash. Citric acid
(you can make over 20% aqueous solution and expose the flask to it for
an hour hours) is great because it is mild acid but a decent chelator.
You can add small amount of some organic solvent like ethanol or
2-propanol to your citric acid solution to assist wetting the surface.
The metallic impurities that do not come off in citric acid will not
come off at pH=3 - If it is metal impurities that are doing it.

My guess is what is killing your protein is more likely some greasy
impurities introduced in manufacturing/machining the stainless steel
container. The manufacturer could have changed the procedure (or the
person) so you may be now getting a product that is greasier than
before.

Potassium hydroxide 5% with some added common sulfonate detergent
(dishwashing liquid or Triton - added in a very small ammount) plus
K3PO4 5% is a wonderful de-greasing/cleaning solution. (Soak for few
hours or overnight. Then rinse well with hot water. Not compatible
with aluminum). You can do citiric acid wash afterwards to be sure -
and to completely neutralise the surface.

"N:dlzc D:aol T:com \(dlzc\)" <N: dlzc1 D:cox T:net@nospam.com> wrote in message news:<9_MVc.5983$ml1.3787@fed1read07>...
> Dear N. Ron:
>
> "N. Ron" <nileshron@rcn.nospam.com> wrote in message
> news:41279475$0$21756$61fed72c@news.rcn.com...
> > Being a biotech firm, we do not have the liberty of adding EDTA or any
> other
> > metal ion scavengers to the solution (due to regulatory hurdles).
> >
> > But looking at the issue another way, can I pretreat the 316L SS vessel
> in
> > anyway to avoid (or reduce) the leaching? A lot of companies soak SS
> vessels
> > in 1 N sodium hydroxide...what does that do from a chemistry standpoint?
> Is
> > there anything else that we can do besides electropolishing and
> passivation
> > as pretreatment?
>
> Don't use any acids based on either chlorine or sulfur. Use of acetic,
> nitric or citric acids will remove free iron, and leave (mostly) chromium
> oxide on the surface (passivation, as you note).
>
> Don't use DI to "clean residues", as DI can amplify any surface problems.
> And surface problems can be created/started by coming in contact with any
> free-iron bearing substance ("dust", metal tools, etc.). This could have
> been by steel shelving contacting the bottom of the container nested in the
> container you received.
>
> Stainless steel is only stainless because of the chromium oxide layer
> (approxmately). Consider glass, ceramic, or titanium (which has its own
> problems) instead.
>
> David A. Smith

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