I have never worked with naptha and very rarely work with organic
solutions at all, so I'm just going to throw out an idea and see how long
it takes for it to be shot down.
Is it safe to assume naptha would not react with aqua regia, and that they
would be immiscible? If so, then add about 1/50th by volume of aqua
regia. Shake the #$%^&* out of it for a long time, or even longer.
Extract the aqueous layer from the bottom of the mixture using a
separatory funnel. Dilute as necessary.
My experience with mercury leads me to believe the mercury in your sample
would become well oxidized by aqua regia and subsequently well stabilized
by the high chloride content of the aqueous phase. I don't know the
relative affinity of naptha for mercuric ions.
Analytical Lab Manager
APL Engineered Materials, Inc.
Urbana, IL 61802
[log in to unmask]
"PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's)."
<[log in to unmask]> wrote on 01/04/2010 05:10:29 PM:
> 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
> 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
> 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
> -----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?
> Geoff TYLER
> Longjumeau, France