In preparation of aragonite shell samples for trace metals analysis, I use buffered hydrogen peroxide to remove organic matter. while this step is effective in reducing concentration of many elements, It seems that with regard to Al, Fe, Zn. Pb and perhaps a few other elements the sample becomes enriched during this process.
interesting question. there are a couple of possibilities. how clean is your H2O2 and buffer mixture? secondly: if you remove organic matter, there will be nothing to stop the metals from adsorbing; dissolved organic matter would tend to keep metals dissolved.
Hi Stan
thanks for the quick answer. from icp-ms measurement my reagents seem clean and are not a source for contamination. Regarding removal of organic matter - I want to measure trace metals in the carbonate, without bias by remaining organic tissue on and inside the shell. the organic matter is often enriched in many metals relative to the carbonate. Thats the purpose of using H2O2. I suspect that ions released from organic matter by the H2O2 are readsorbed onto the suspended solid.
Hi Yitzhak. Yes that seems a reasonable conclusion: the organics will be full of metals. One possibility might be to add a new chelator to the water (EDTA for instance) after the digestion with H2O2. another might be to add something to stop re-adsorption: people use for instance titanium ions to desorb metals (iron especially) from cell walls to find out how much iron is inside the cells. but I dont know if this solves your problem. with you success.
There are in the soils analytical literature numerous analytical methods to determine the amount of adsorbed cations on soil particles. May be you can use these methods to release the freshly adsorbed metals. See attached (sorry, old) article which gives some references and determining adsorbed metals on sediments
Article Trace metal analysis on polluted sediments. Part II: Evaluat...
In our recent investigation of REE in biogenic carbonates we found that hydrogen peroxide treatment is not as effective in 'cleaning' the samples. Instead a H2O2 plus a bit of weak HCl solution shall do the 'trick'. See the paper by Zaky et al. 2015 A new sample processing protocol: an important update for procuring reliable REE signatures. Permophiles 61: 97-98 (you should be able to find it on my Researchgate page).
Thank you all for your helpful ideas.
I will try the techniques for removing the adsorbed ions, and will try to use a week acid leach as well, after the H2O2 step.
After a talk with Steve Weiner I realized that I will not be able to separate the intra-crystaline organic matter. However, the trace elements signal from this part seems stable, so I am not that worried about it. mainly concerned about remains of soft tissue and algae inside and between shells.
Thank you all again
- Badges
- Science topic