Dear Mary, Steve and others on the list,
We have not used liquid argon since the earlies. Of course, we are not doing overnight unattended runs. A simple 3 or 4 port brass manifold with dual-stage regulator is all we use. Each port has its own valve, so you can change tanks on the fly without shutting the plasma off, like changing lines in hockey.
I have heard it said that argon boiloff from a dewar is cleaner than argon from pressurized cylinders. Our source of argon tanks is very good, there is very little mercury or xenon in our argon. We usually could not detect mercury ions at all using high sensitivity instruments like a magnetic sector or the Bruker/Analytik Jena quadrupole device. There have been a few cases where we used tanks from a different supplier that were dirty, sometimes with so much organic stuff we could not start the plasma.
I could send photos of what we use if that would help.
Ames Lab USDOE
Iowa State University
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: Tuesday, June 12, 2018 8:16:16 AM
To: [log in to unmask]
Subject: Re: Looking for recommendations for a changeover manifold for a 1 ICP-MS lab
It has been over 15 years, so I do not remember details, or the contractor who installed the system, but we had a dual external mini-bulk argon tank system installed with a manifold that fed I think six ICP-MSs. The minibulk dewars were used one at a time so that when one got low, you could switch to the other with a valve (which answers your switching question), and so that when you needed to blow off accumulated heavier liquid noble gas accumulation from the bottom, you always had one tank full. You don't have to have a dual system, just telling what we had. I had to choose and order the correct i.d. tubing from outside to inside. I chose medical grade stainless steel with Swagelock connections rather than welding or copper with solder. This was more expensive, but prevented welding/solder particles in interior of the tubing. Cheaper stainless steel may or may not still have rolling oil. Some say that mercury is exhaled from copper tubing at detectable levels. I don't know, because I did not choose copper. Our supplier was Airgas, but minibulk or microbulk dewars with manifolds can be installed in consultation with most gas suppliers: Air Products, Praxair, Tescom, American Gas Products, etc. You will have to set up how often you want them filled with the supplier anyway.
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
From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's). <[log in to unmask]> On Behalf Of Carson, Mary C (FDA/CVM)
Sent: Monday, June 11, 2018 5:11 PM
To: [log in to unmask]
Subject: Looking for recommendations for a changeover manifold for a 1 ICP-MS lab
I did search the archives, and the most recent post seems to date to 2004. We have 1 ICP-MS and 1 operator (me). I do other things sometimes. So I find the ICP-MS seems to alternate between sitting idle, sometimes for weeks, and being used 24/7. Liquid dewars of argon inevitably blow off during idle times, sometimes leaving me without argon. I will sometimes use 2 compressed cylinders simultaneously to get through an overnight run. I am think of installing a manifold system, preferably that could take either cylinders or dewars. Getting a 16 cylinder pallet doesn't really seem practical for my lab setup. I have one quote so far for a 4 cylinder manifold, but it uses a brass header, which I believe would be part of the flowpath. Is this problematic when doing trace analysis? I am under the impression I should stick with SST. Are there vendors out there other than Airgas or Tescom that I should be looking at? Does anyone else use a changeover system that can be supplied by either compressed cylinders or liquid dewars, depending on anticipated use?
Mary C. Carson, Ph.D.
Center for Veterinary Medicine
Office of Research, Division of Residue Chemistry U.S. Food and Drug Administration
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