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PLASMACHEM-L  June 2018

PLASMACHEM-L June 2018

Subject:

Re: Magnet composition

From:

"Lacroix, Deborah ([log in to unmask])" <[log in to unmask]>

Reply-To:

PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's).

Date:

Wed, 20 Jun 2018 17:49:41 +0000

Content-Type:

text/plain

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Parts/Attachments

text/plain (80 lines)

Unfortunately, I have already received these samples that have been dissolved in aqua regia, so that is all that I have to work with.  It sounds to me like the sample should be dissolved/prepped in different matrices for the different groups/analytes of interest. I'm just not sure I can give them accurate data based on the solution that I have now.  Should I see if they can prep the samples via different methods in the future? My feeling is that bad data is better than no data and I want to analyze give these researchers good data.  I am more than happy to analyze the data, but I want them to be informed of any issues when I report it.


Also, since we are getting more and more of these types of samples, would a QQQ be a more appropriate instrument for some of these analytes?


Thank you so much for all your input!


Debbie Lacroix

Analytical Chemist

University of Idaho

Center for Advanced Energy Studies (CAES)

995 University Blvd

Idaho Falls, ID 83401

Office: 208-533-8153

E-mail: [log in to unmask]<mailto:[log in to unmask]>



________________________________
From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's). <[log in to unmask]> on behalf of Pappas, Richard Steve (CDC/ONDIEH/NCEH) <[log in to unmask]>
Sent: Wednesday, June 20, 2018 7:33:34 AM
To: [log in to unmask]
Subject: Re: Magnet composition

Oops, I meant for my GUESS to say, "For every 3 mL HCl, ... 1.5 mL HF.)

R. Steven Pappas, Ph.D.
Team Lead, Tobacco Inorganics Group
Centers for Disease Control & Prevention
4770 Buford Highway, NE
M.S. F44, Building 110
Atlanta, GA 30341-3717, USA

-----Original Message-----
From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's). <[log in to unmask]> On Behalf Of Pappas, Richard Steve (CDC/ONDIEH/NCEH)
Sent: Wednesday, June 20, 2018 9:22 AM
To: [log in to unmask]
Subject: Re: Magnet composition

Good morning, Debbie,
If I were you, I would just thank God that I was not also asked to determine He, Ne, Ar, Kr, Xe, and Rn as well!!!
More than interferences, you are going to have losses of some elements, memory effects/carryover if not careful. Also, if you have never analyzed for aluminum, you need to be aware that it is ubiquitous, even in some high purity acids, so if you dilute too far, background can become a problem.
Are you REALLY constrained by the limit that you MUST use aqua regia? Aqua regia will be fine for some but not all of your analytes.
The KED mode with the 7900 ought to be able to handle most polyatomic interferences.
There is no law that says you have to analyze them all in one method. You can optimize analyses by dividing them into groups.
As an example, Au, Pd, Pt, Ag are easily reduced in nitric acid alone. Ag is even photocatalytically reduced, so you want to keep dissolved materials away from light as long as possible. They are also soft acid cation metals, so they are stabilized in solution, reduction is slowed down if they are coordinated with soft base anion ligands like chloride or sulfur. So your aqua regia digest could be diluted 1/200 in water, leaving chloride at approximately 3.75%, well sufficient to maintain these cations in solution long enough to analyze. Fe would be happier in dilute HCl with this group also. Since you do not have silicate matrix(?), Cr would be happy in this group. Even with chloride ligands, I would not trust Ag to remain stable in solution very long.
Bismuth is an intermediate cation metal. It MIGHT be analyzeable in the same solution with the precious metals, but I am not sure. It is soluble in fairly concentrated HCl, but when you dilute the chloride, at some point, it will precipitate as insoluble BiOCl. I do not happen to know how far you can dilute Bi in aqua regia. Maybe another reader knows. As a precaution, it may be better off in a solution that is predominantly nitric acid and does not have HCl. Al is likely to be happy in EITHER the diluted aqua regia group, or a predominantly nitric acid group.

You will probably lose tin in the digest unless you have significant HF. Tin forms a volatile chloride that boils at 117°C, and you will have a very high Chloride concentration during the digest. Unless you add enough HF to shift the tin equilibrium away from volatile chloride complex to fluoride complex, you will lose it from digestion vessel headspace when you open the vessel, and in vessel walls. I do not know what that concentration would be, but I would estimate that the fluoride concentration would have to approach the chloride concentration. Since concentrated HCl is ~12 M; and concentrated HF is ~29 M, I would guess that for every 3 mL HF, you might need about 1.5 mL HF to stabilize Sn in less volatile fluoride form, but that is a guess. You need HF for maintaining Zr solubility anyway, so however you group your analyses, Zr should go with Sn. Ge, Mo, Tb should be happy in this group as well.

If you had a nitric acid only digest, Al, Bi, Co, Cu, Dy, Gd, Mn, Nd, Ni, Pr, Sr, V, would be perfectly happy in this. Some of these will be happy in other matrices. For example, we have methods in which Al, Co, Cu, Mn, Ni are in solution that is predominantly dilute nitric acid, but contains dilute hydrochloric and hydrofluoric acids as well. I am just trying to make things “…as simple as possible, but no simpler…” (Albert Einstein).

R. Steven Pappas, Ph.D.
Team Lead, Tobacco Inorganics Group
Centers for Disease Control & Prevention
4770 Buford Highway, NE
M.S. F44, Building 110
Atlanta, GA 30341-3717, USA

-----Original Message-----
From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's). <[log in to unmask]> On Behalf Of Debbie Lacroix
Sent: Tuesday, June 19, 2018 8:21 PM
To: [log in to unmask]
Subject: Magnet composition

I have been asked to measure the composition of magnets dissolved in aqua regia.  The analytes of interest are Al, Bi, Cr, Co, Cu, Dy, Gd, Ge, Au, Fe, Mn, Mo, Nd, Ni, Pd, Pt, Pr, Ag, Sr, Tb, Sn, V, Sn and Zr. I have an Agilent 7900 ICPMS and a Thermo 6500 iCAP OES available.  I'm having trouble determining where to begin as there are so many interferences, analytes that need to be in or not be in HCl, some that need to have HF, some that run better on OES and others on MS.  Any advice would be greatly appreciated!

Debbie Lacroix
Chemist
University of Idaho at the Center for Advanced Energy Studies (CAES) Idaho Falls, ID

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