methylene_beam
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Reducing Hg2+ to Hg0
hello all,
I am working on a project where I am trying to detect mercury. I am using a mercury fluorescence detector so i require that all my Hg be in the 0
state.
my question is could I use an aqueous metal reducing agent like hydroquinone maybe a 0.05m solution to reduce all the Hg2+(as the chloride) to the Hg0
state where it can be detected.
My main question is does hydroquinone effectively and quickly reduce all the Hg?
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methylene_beam
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The samples of Hg i am working with are 1 ppm and lower. So i never see the formation of the reduced metal.
here is how my process works:
Hg aqueous sample is mixed with hydroquinone in a chamber. assuming the hydroquinone acts as a reducing agent the new Hg0 should have low enough vapor
pressure to be swept by an inert gas (300ml/min) into the Hg flouresence dector.(detector cant recieve aqueous samples)
when I mix water with the aqueous samples of Hg i still get a peak. However, when the aqueous samples are mixed with a 0.05M hydroquinone solution the
peak area is always much greater.
peak area for a typical run 1PPb solution H
water area: 2500
0.05M hydroquinone area: 7500
I feel as though this experimental data shows that hydroquinone is acting as a reducing agent by increasing my peak area by about 3 fold.
do solutions of Hg(Cl)2 in water revert back to Hcl and Hg0. I am trying to figure out why when i use water i still get a small signal.
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methylene_beam
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like I was saying my data is showing a much greater peak area when hydroquinone is used. but i want to know why i am seeing a signal when water is
used. My gut is telling the the the standards is am using must auto reduce in solution considering they arent in amber bottles and Hg(Cl)2 is a salt
and could hydrolyze back to HCl and Hg(0).
edit: I made fresh solutions of Hg(Cl)2. There was still a small signal with water but not as as much as the older solutions(1 year old)
I preped a solution of Hg(NO3)2 and there was no signal in water. but there was not signal with reducing agent. Upon reading I found that it takes
strong reducing agents to reduce the nitrate.
[Edited on 7-3-2012 by methylene_beam]
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Nicodem
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In organic synthesis, NaBH4 is used to quench all the Hg(II) species to Hg(0). NaBH4 is well soluble in water and its major volatile side product is
hydrogen which is unlikely to interfere with the measurement. The disadvantage of NaBH4 is in that is fairly rapidly decomposes in acidic aqueous
medium, so you would need to use a basic buffer on your samples to make the method reliable and independent of the samples initial pH. In fact, such a
sample treatment was proposed for atomic absorption spectrometry (see DOI: 10.1021/ac60363a001).
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methylene_beam
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Quote: Originally posted by Nicodem  | | In organic synthesis, NaBH4 is used to quench all the Hg(II) species to Hg(0). NaBH4 is well soluble in water and its major volatile side product is
hydrogen which is unlikely to interfere with the measurement. The disadvantage of NaBH4 is in that is fairly rapidly decomposes in acidic aqueous
medium, so you would need to use a basic buffer on your samples to make the method reliable and independent of the samples initial pH. In fact, such a
sample treatment was proposed for atomic absorption spectrometry (see DOI: 10.1021/ac60363a001). |
I originally wanted to go the boro hydride way but i remember the when you add it to water it evolves H2 and ultimately decomposes.
my conditions dont allow me to have the reducing agent in anything but water.(no organic solvent) i have been making up my hydroquinone solutions and
adding a drop of ammonium hydroxide.
would a 0.05M solution of boro hydride still be viable? how long for decomp times?
over the course of that day the hydroquinone solutions darken to a deep red. I remember from undergrad the hydroquinone solutions go bad (oxidation to
benzoquinone ?) over time. perhaps if i made the solutions up in a amber bottle and made them under nitrogen i can avoide this? maybe degas? anyone
got any experience with hydroquinone solutions?
EDIT: anyone knoe if Hg(Cl)2 can revert back to HCl and Hg(0) that would explain some things
[Edited on 7-3-2012 by methylene_beam]
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ScienceSquirrel
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Would anyone mind if I pruned the thread so only the posts relevant to the original post remained?
I think this is a good and valid question but there are some irrelevant diversions.
If anyone objects I will leave it alone.
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Hexavalent
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I would have to agree with SS, there are already too many irrelevant posts which makes understanding the topic here slightly more unclear and
difficult.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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unionised
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Borohydride or Sn(II) are traditional
Here's the first reference Google found about it.
http://onlinelibrary.wiley.com/doi/10.1002/9780470027318.a08...
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methylene_beam
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tryed Sn(II) having solubility issues even sonicated for a while stayed as a white suspension. I also dont want that near my HPLC pumps. Don't know
about borohydride in the pumps either. thanks though
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methylene_beam
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| Quote: Originally posted by ScienceSquirrel | Would anyone mind if I pruned the thread so only the posts relevant to the original post remained?
I think this is a good and valid question but there are some irrelevant diversions.
If anyone objects I will leave it alone. |
prune away. I am talking about small scale reduction and sweeping the generated Hg(0) into the detector
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methylene_beam
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mind uploading the full text. I not in the lab right now and dont have tha data base at hand
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bfesser
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<strong>methylene_beam</strong>, what other species are likely to be present in the water samples? As you know, most chemical reactions
occur as an equilibrium. In analytical chemistry, it's important to know what species are present so that the equilibrium can be shifted as far as
feasible in favor of the desired analyte. And, given the level of public paranoia surrounding mercury and environmental mercury contamination, it's
likely that someone has already come up with a highly sensitive and reliable technique based on the fluorescence detector by now. Would it be worth
searching for published techniques, or are you trying to come up with your own/something new?
Here is a page that you should probably look over:
http://water.epa.gov/scitech/methods/cwa/metals/mercury/inde...
I've also requested the papers mentioned earlier by Nicodem and unionised in the <a href="viewthread.php?tid=19098#pid240106">Wanted References
and Needed Translations (8)</a> thread, on your behalf. <!--Since you won't have access to that thread, I'll make sure they're available
from this one, once uploaded.-->
<hr width="300" />
<strong>ScienceSquirrel</strong>, please prune the thread. Apparently some dumdums don't read threads beyond the title before replying.
<hr width="300" />
<strong>AJKOER</strong>, we really need to get you your own section for hypochlorite chemistry. However, your process seems unnecessary.
[Edited on 3/8/12 by bfesser]
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methylene_beam
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| Quote: Originally posted by bfesser | <strong>methylene_beam</strong>, what other species are likely to be present in the water samples? As you know, most chemical reactions
occur as an equilibrium. In analytical chemistry, it's important to know what species are present so that the equilibrium can be shifted as far as
feasible in favor of the desired analyte. And, given the level of public paranoia surrounding mercury and environmental mercury contamination, it's
likely that someone has already come up with a highly sensitive and reliable technique based on the fluorescence detector by now. Would it be worth
searching for published techniques, or are you trying to come up with your own/something new?
|
as of right now there are no other species just Hg(Cl)2 in prepared solutions in volumetric flasks. these are standards to ultimately design a
calibration curve. when i go to test it on human tissue i am going to nuke everything with bromine monochloride. i have a procedure for processing
flesh for analysis.
essentially I have a solution with some concentration of Hg(cl)2. lets say its 10 BBP. It is injected into the HPLC. for solvent A i have pure water
on sovlent B i have a 0.05M solution of hydroquinone in base. I can vary the concentrations on both right now its 50:50
1)injected material meets the mobile phase.(no column just a tube that connects it to the cell)
2)once they meet the hydroquinone should reduce the Hg(Cl)2 to Hg(0)
3) now that mercury has been reduced it is swept from the cell with a carrier gas into the detector
i didn't make this thread for comments on the construction of the instrument. I know that works.
rather simply does hydroquinone reduce mercury thats all I am asking. from that data I have gathered I it looks to work.
so again i am summing up my 2 questions.
1) will hydroquinone reduce Hg(cl)2?
2) do solutions of Hg(Cl)2 auto reduce back to Hg(0) and HCl in the presance of water
I slowed the flow rate(0.5ml/min to 0.3 ml/min) peak tripled in size and resolved to base line much faster. This leads be to believe that the Hg(Cl)2
spent more time in the presence of the reducing agent. corresponding to an increased presence of elemental Hg
can someone please prune this thread of people that misunderstood what i was asking
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ScienceSquirrel
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Thread Pruned
7-3-2012 at 17:13 |
ScienceSquirrel
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I have done a quick prune.
Apologies to anyone who thinks that I have treated them unfairly.
This thread is about the detection and measurement of mercury at low levels.
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AJKOER
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My research indicates a major simplification of the problem of testing for Mercury in water. To quote from Wikipedia:
"Methylmercury" is a shorthand for "monomethylmercury", and is more correctly "monomethylmercuric cation". It is composed of a methyl group (CH3-)
bonded to a mercury atom; its chemical formula is CH3Hg+"
and, most importantly:
"Methylmercury is formed from inorganic mercury by the action of anaerobic organisms that live in aquatic systems including lakes, rivers, wetlands,
sediments, soils and the open ocean.[5] This methylation process converts inorganic mercury to methylmercury in the natural environment."
Methylmercury appears to accumulate in fish, where upon consumption by people, can result in poisoning. As such, the test reagent used should be
particularly powerful in detecting Methylmercury. However, for lab work I do understand using Mercury chloride as a benchmark as upon adding HCl to
stabilize and a powerful oxidizer like BrCl (see link below), one is forming some Mercury chloride and this is must safer to work with than say Methyl
chloride or worst, deadly Methyl bromide.
Per previously supplied material above at: http://water.epa.gov/scitech/methods/cwa/metals/mercury/uplo...
Current testing compounds employed include oxidation by BrCl followed by removal of halogens with NH2OH.HCl, followed by reduction with SnCl2 to form
the volatile Hg.
As guidance on possible other compounds to test for the presence of Methylmercury, I suggest reviewing the list of incompatible compounds per
Methylmercury MSDS:
"Incompatibilities with Other Materials: Metals, aluminum, ammonia, chlorates, copper, copper alloys, ethylene oxide, halogens, iron, nitrates,
sulfur, sulfuric acid, oxygen, acetylene, lithium, rubidium, sodium carbide, lead, nitromethane, peroxyformic acid, calcium, chlorine dioxide, metal
oxides, azides, 3-bromopropyne, alkynes + silver perchlorate, methylsilane + oxygen, tetracarbonylnickel + oxygen, boron diiodophosphide'
Link:
http://fscimage.fishersci.com/msds/96252.htm
Bfesser: I am sorry but my suggested ClO2 is on the list along with a generic reference to halogens. Note, the current use of BrCl, which with Methyl
compounds, is probably best left to professionals.
-----------------------------------------------------
Here is a small suggestion on how to make the current test for Hg more insightful by testing for trace amounts of Methyl also. Add bacteria to a tap
water solution containing a trace amount of say Methyl alcohol and a standard tap water solution with no bugs. Both solutions have, however,
equivalent trace amounts of Hg. Add a very dilute HBr/H2SO4 solution to both. If any Methyl bromide is formed, there should an accompanying
significant visual decline with time in population density of the bacteria exposed to Methyl bromide (lethal in ppm). Potential issue with this test
for Methyl is that the tap water may already have significant Methyl contamination, so no difference may be observed.
[Edited on 8-3-2012 by AJKOER]
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Nicodem
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| Quote: Originally posted by methylene_beam | I originally wanted to go the boro hydride way but i remember the when you add it to water it evolves H2 and ultimately decomposes.
my conditions dont allow me to have the reducing agent in anything but water.(no organic solvent) i have been making up my hydroquinone solutions and
adding a drop of ammonium hydroxide.
would a 0.05M solution of boro hydride still be viable? how long for decomp times? |
These issues were already addressed. If you would have been interested enough, you would have read the article I refereed you too. Unionised also gave
you some reading material. Perhaps it is now time to read articles?
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