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Subject Topic: Chrome 6 test method Post ReplyPost New Topic
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seogsoo
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Posted: 21 March 2011 at 9:51pm | IP Logged Quote seogsoo

Dear All

Everyone knows that there is some inaccuracy issue about current test method. But is there any official report about that?

Regards

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BenD
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Posted: 22 March 2011 at 5:22am | IP Logged Quote BenD

Dear Seogsoo,

In Europe we now use the ISO 17075 to analyse Cr VI content in leathers.
This test method is accurate but cannot detect Cr VI below 3ppm.

The previous test method (CEN TS 14495) used in Europe was not as accurate. After many years of debate the detection limit was set to 10 ppm due to interference that might occur during the analysis .

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kallenwe
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Posted: 22 March 2011 at 9:02am | IP Logged Quote kallenwe

There are several articles about hex. chrome determination published in JALCA, just search the journal for "hexavalent" or even hex.  Other publications such as Leather Magazine, Leather Manufacturer, JSLTC as well as the German, Brazilian and Spanish journals have also published work on this subject. 

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seogsoo
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Posted: 22 March 2011 at 11:59pm | IP Logged Quote seogsoo

Thank you. I will check as well.
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DavidR
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Posted: 03 April 2011 at 9:09am | IP Logged Quote DavidR

I am in the hinterlands where internet access is stop and go!  I had developed a qualitative "spot-test" for Chrome six in liquids that might be of use to you, as it's sensitivity is good enough for detecting fractions of a ppm!  Take 2ml of your sample solution in a test tube and add to it 5 ml of 1N reagent-grade sulphuric acid and shake well with care not to contaminate the liquid (use a little bit of clean plastic film on the test tube as you cover with finger).  Add about 2 ml of colorless (if necessary freshly distilled) Toluene that will float on the top of the aqueous layer, add about 100-300 mg of powdered KI and shake wel and keep out of the light for five or ten minutes.  If there is any chrome six or other strong oxidant, the iodine formed will dissolve into the overlaying toluene solvent and color it purple.  I had been able to detect chrome six in fractions of a ppm in made-up solutions.  I would guess that a water extract  of leather bits or shavings would also show if appreciable chrome six were present, but never tried it!  I used the test to show pollution authorities that their reports about chrome six were positive false readings.  If they balked too much I would point out that then their chemical oxygen demand tests were also wrong, especially since they dertermind QOD with out removing chloride before determining!

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kallenwe
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Posted: 04 April 2011 at 9:52am | IP Logged Quote kallenwe

there is a similar phase separation method that directly chelates and extracts hex. chrome.  Would that be more definitive?  I believe it is presented in Methods for Examination of Water and Wastewater, and perhaps SW 846 (EPA Solid Waste Methods).  In fact I believe the title is actually "Chelation and Extraction Method."  Ever heard of it?  It is indeed very sensitive as you can actually concentrate chrome into the non-aqueous phase.  On the other hand chrome soaps and organically chelated chrome can be a serious false indicator. 

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DavidR
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Posted: 06 April 2011 at 5:20am | IP Logged Quote DavidR

This technique of concentrating iodine in an organic solvent for great sensitivity has been employed in classical iodimetric titrations where a small amount of carbon tetrachloride in the bottom of the Erhlenmayer flask, instead of on-the-top like toluene in the suggested spot test for hexavalent chrome, will greatly concentrate in a small volume the aqueous iodine present as triiodide in the aqueous phase:  I2 + I- => I3-, much as starch-iodide paper shows the presence of a strong oxidiser.  If there is no chrome six or other strong oxidizing material, it will show it not present and hence avoid delicate and complicated testing for chrome six!  If there is purple in the the toluene, there might be chrome six and more annalisis needs to be done, but if there is no chrome six present, then the organic solvent remains colorless and no more testing has to be done!

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kallenwe
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Posted: 06 April 2011 at 7:50am | IP Logged Quote kallenwe

Would chrome soap, heavily masked chrome or other organically chelated chrome 3 also color the solvent phase as it sometimes does in the chelation extraction method?  Of course the chelation extract is not purely dependent upon color as the solvent is often driven off and the chrome digested for a specific chrome determination by instrumental followup, ie ICP or AA.  The solvent phase is simply the means to concentrate the chrome. 

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DavidR
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Posted: 25 April 2011 at 1:45pm | IP Logged Quote DavidR

I am not understanding what you are saying!  Trivalent chrome will not even dissolve in the toluene layer no matter how much it is complexed.  The idea that the Iodine formed by oxidation and greatly stabilized in the aqueous phase as the triodide anion, wil be removed and concentrated in the superlaying toluene phase.  Any salts or even soaps of chrome III would not go to the toluene at all.  This test would tell you if Cr plus 6 is possible or not!  If not, this is a definite and sufficient test that would categorically discard the need for any more testing and we can categorically can say that hex chrome was not present at the detection limits.  Light can result in the formation of hexavalent chrome, especially UV present in ordinary flourecent tubes!

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DavidR
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Posted: 25 April 2011 at 1:49pm | IP Logged Quote DavidR

The chrome six anionic species might be reacted in some way to be soluble in toluene such as chromyl chloride liquid, but it would form Iodine in the presence of triodide as well!  The absence of reddish pink color in the toluene is a positive proof that chrome six species are not present!  No other test is rerquired to indicate whether it could be!

Edited by DavidR on 25 April 2011 at 1:52pm


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