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Author: Subject: Diphenyl Carbazide Detection of unknown

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[*] posted on 12-2-2006 at 11:20
Diphenyl Carbazide Detection of unknown

Hi, I am currently using 1,5-Diphenylcarbazide to detect mercury in fish tissues. Though this reagent detects mercury, it can also detect other metallic ions. How can I make sure it only detects the traces of mercury within the fish tissues?
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International Hazard

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[*] posted on 12-2-2006 at 11:29

With some difficulty. You might be able to form complexes of some of the other metals with something. eg citrate might complex copper well enough to stop it reacting with the diphenylcarbazide.
The other way round the problem would be to reduce the mercury in the sample to the free metal, distill it, redisolve it in oxidising acid, then measure it. Because there will only be traces of mercury the health risks from the Hg vapour shouldn't be too great but I still wouldn't want to try it. Also, the losses would probably be considerable.

Trace metal analysis was never easy. I think you might want to look into comercial instruments for this.
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Biochemicus Energeticus

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[*] posted on 13-2-2006 at 13:31

I agree with unionised - quantitative chemical determination is going to be difficult, as amounts are so small and other trace ions interfere. There are numerous analytical and qualitative ways, but they normally work with greater amounts.

I suppose it might be a good idea to first solubilise the fish tissue, and then precipiate all Hg (and other trace ions, such as PbS) with H2S. The resultant precipitate is dissolved with HCl, and all soluble products are discarded. The remaining insoluble PbS can be redissolved in aqua regia, and turned into i.e. Hg(Ac2)- this should not contain much insoluble ions other than Hg). Quantitative determination will have to be spectrophotometrical (UV), also blank against a clean solution of HgAc2 to determine how the spectrum differs (as by other trace ions).

You can also use techniques such as atomic absorption spectroscopy, but I don't know if they work quantitively.
Forensic labs/ books relating to their techniques might also be a good starter.

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[*] posted on 16-2-2006 at 06:15

Mercury by AA is not usually done in an open flame or in a graphite furnace. It usually will use a heated quartz cell and metal hydride mercury vapor generation.

In any case what I am saying is, if you want an instrumental assay for mercury you may have to find someone with an AA with the specific attachements to assay for mercury, or a lab with a vented ICP.
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[*] posted on 16-2-2006 at 17:27
This is the standard NIOSH method for mercury analysis using AA. This could be adapted to fish tissues by digesting a known mass of fish tissue followed by dilution to known volume and comparing AA results to a set of concentration standards. Your result will be mass / volume which can then be back tracked to mass / mass and hence a % w/w mercury level can be determined (i suppose % w/w is what you would be looking for?)

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