Dear Jeoff, Steve
We run a direct mercury analyzer, but the LOQ is set to 5 ppb. I don't see
a way in decreasing this value significantly.
Daniel
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"Pappas, Richard
Steve
(CDC/CCEHIP/NCEH) An
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Gesendet von: Kopie
"PLASMACHEM-L:
Analytical Thema
Chem.(ICP's, Re: digestion method of naphtha
DCP's, MIP's)." for sub ppb Hg determination (by
<PLASMACHEM-L@LIS hydride) ICP-OES
TSERV.SYR.EDU>
05.01.2010 15:57
Bitte antworten
an
"PLASMACHEM-L:
Analytical
Chem.(ICP's,
DCP's, MIP's)."
<PLASMACHEM-L@LIS
TSERV.SYR.EDU>
Jeoff,
I think Duane and Vinay made good shots at it, considering possible
problems. I think the better approach to this would be a cold vapor AA or a
direct mercury analyzer.
At least Leco, Nippon, maybe CEM, and Milestone sell these, probably worth
looking into.
Steve Pappas
CDC
________________________________
From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's). on behalf of
Pappas, Richard Steve (CDC/CCEHIP/NCEH)
Sent: Mon 1/4/2010 6:10 PM
To: [log in to unmask]
Subject: Re: digestion method of naphtha for sub ppb Hg determination (by
hydride) ICP-OES
Geoff,
Like Juan, I think you will lose Hg during digestion. Nitric acid will
is not oxidizing enough for Hg, may just catalyze its reduction, causing
losses.
There are people who do run organic solvents, but generally they dilute
solutions like naphtha in something like xylenes or alkanes. Still, you
say you need to concentrate, not dilute; and I would NOT try a stronger
desolvating system like Aridus or Apex. They are good for many elements,
but Hg is the exception. The organic solvents are good solvents for any
reduced elemental Hg that you already have, but any neutral Hg will
stick all over a pfa surface at elevated temperatures and cause a big
memory effect.
Therefore, the Peltier cooled chamber is as far as I would go with
desolvation.
The trouble with trying to get Hg into an aqueous phase is that not all
of it is likely in ionized form. You probably have neutral element also.
You did not mention your nebulizer and liquid flow rates. If you can add
some diethyldithiocarbamate ammonium salt, it may help complex at least
the ionized form and stabilize it in the naphtha. Unless the naphtha is
cruddy, you can probably find an application note from your instrument
supplier regarding running organics such as gasoline, etc., but just run
it neat if it is not cruddy.
A lower flow, higher pressure nebulizer, preferably quartz, not
polymeric, may help you decrease the plasma loading with organic solvent
and actually increase signal at a lower liquid flow rate, say 100 - 200
microliters/min rather than mL/min.
If you really want to concentrate it, you may have a problem. You can
grab the ionic Hg with sulfur ligand chelating agents like Juan
suggested. However, if there has been any Hg reduction (and I'll bet
there has been - just sample the naptha head space without opening the
container and run a high temperature GC - > 350 degrees C into an ICP),
the sulfur ligand won't necessarily grab the neutrals.
For concentration, you might try stirring in the presence of dilute
nitric acida to catalyze reduction and adsorbing it with gold, copper or
similar particle powder, then use either a direct mercury analyzer or
heat the adsorbent to drive off the Hg.
That is a bit nebulous... "maybe it will work..." Sorry.
Steve Pappas
CDC
-----Original Message-----
From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's).
[mailto:[log in to unmask]] On Behalf Of (Geoff Tyler)
Sent: Monday, January 04, 2010 11:30 AM
To: [log in to unmask]
Subject: digestion method of naphtha for sub ppb Hg determination (by
hydride) ICP-OES
Hello everyone
I have a puzzle that hopefully someone can help me.
We have a need to determine sub ppb (ug/L in solution) of Hg in naphtha
by ICP-OES.
While the peltier cooled Spray chamber on the ICP-OES will get us to
about 5 ppb Hg, we need to think of digestion & pre-concentrate for
aqueous hydride generation Hg determination to achieve the goal of sub
ppb LOQ. (so the LOD needs to be < 0.2ppb).
I have thoughts of conc HNO3 attack on neat naphtha & then careful
pre-concentration. I can see of sorts of problems like:
1 Would Conc HNO3 digest all the naphtha?
2 How to pre-concentrate the digested aqueous solution, without
loss of Hg
maybe a closed vessel microwave oven will solve that ?
3 How to ensure oxiding state is not too strong to prevent NaBH4
(or SnCl2) reduction to enable reduction to Hg vapour.
There is insufficient need to justify a specific low level Hg analyser
in petroleum ( like that supplied by PSA )
Any ideas?
cheers
Geoff TYLER
HJY,
Longjumeau, France
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