Letter 34001

Hexavalent chromium emissions from stainless steel parts [No. Carolina] 

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A client of ours needs to test stainless steel tools they make for the medical and pharmaceutical industry for hexavalent chromium to show that none is emitting from the surface of the tools. They are looking for a GM method where you boil the parts in deionized water, add acid, then add and indicator and analyze the sample for hexavalent chromium using spectrophotometry. We can't find this method. Has anyone heard of such a method and know where I might get a copy? Or heard of a similar method for analyzing hexavalent chromium? Any help would be appreciated.

Lorri White
- Durham, NC, USA

The indicator you are looking for is called 1, 5 diphenylcarbohydrazide. It reacts with hexavalent chromium in solutions at low pH (~ 1.0) yielding a red violet color.

Methods for the determination of hexchrome in water can be found in various methods manuals, including "Standard Methods for the Examination of Water and Wastewater".

Dave Wichern - Bronx, NY, USA

The test method you're referring to is GMW 3034. IMR Test Labs in Lansing N.Y. has processed material under this method for us. The detection limit for the analysis is 0.01 micrograms per gram (ppm).

Steve Richardson
- Randolph, MA USA

You might well be able to get hex chrome from the surface of parts that have been plated then chromated, but there's no way that you can get hex chrome from stainless steel. The realities of physics and chemistry shouldn't be ignored - why waste time and money testing for something that cannot possibly be there?

Bill Reynolds
- Melbourne, Victoria, Australia

I know this is an old thread, but as someone who has achieved some notoriety in the field of hexavalent chromium, I thought I would put in my two cents worth. Stainless steel is 'stainless' because the oxide film is thin and highly adherent. It is produced by the oxidation of the surface. In order to passsivate the surface, it is generally treated with a passivation solution, which can be (see ASTM A-967 [link is to spec at TechStreet] for details) - nitric acid plus sodium dichromate, nitric acid, or citric acid. It is uncommon today, but not unknown, to use nitric acid and sodium dichromate. Inadequate rinsing would leave hexavalent chromium on the surface of the part. By the way, in case anyone is interested, stainless steel does not generate hexavalent chromium (to the best of my knowledge and experience) in the ASTM B-117 [link is to spec at TechStreet] Salt Spray Test.

Tom Rochester Plating Systems & Technologies, Inc.   Jackson, MI, USA

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