I want to determine Pb ratios in marine sediments by ICP-MS. We have a Quadropole ICP-MS (X series II by Thermo). I wanted to know if anyone has used any of the available reference sediments and whether there are some comments on this (like how easy is to digest etc).
Hi Eleni, before you embark on your mission, you may want to make sure that the variations you expect to see in the ratios are such that they can be measured by Q-ICPMS, since the uncertainty on the ratios is a lot larger than when you use a MC-ICPMS.
Dissolution techniques will depend on the type of sediments, and what you're interested in. Sediments that contain resistant silicate phases such as zircon will need to be dissolved (using HF/HNO3) in HP digestion vessels (or prolonged microwaving) - unless you are not interested in the Pb that the zircons may be bringing in, of course. Carbonates are lots easier to digest, but contain lower concentrations of Pb.
Good luck!
Hello Marlina. Thank you very much for your reply. I have actually determine Pb ratios on the sediments, to see exactly what you say and the variations where very high, corfirming my predicts. The sediments come from Elefsis Bay in Greece, one of the heavier polluted bays in Mediterranean Sea, surrounded by a wide industrlian zone where Pb anthropogenic imputs have been big, especially in the past few decades. The dissolution techique we always use for sediments that end up to ICPMS does include HP microwave digestion with HF and HNO3 with many steps and 8hours total digestion. So, why did I ask the question....?! Because I need to repeat the analysis with a reference material to be sure my results will be accepted for publishing!
Aha, that explains a lot of things. If you are looking at contamination, then of course you are likely to see the variations you hope for, even with a Q-ICPMS.
Have you checked on the MPI site for geological reference materials (http://georem.mpch-mainz.gwdg.de/) to check what values are published on reference materials? - and from those publications you may be able to find out how they were dissolved. But it sounds like you are doing a good job regarding the dissolution process anyway. If you have trouble finding a sedimentary reference material that is well-characterised, then you could take a granite or granodiorite (such as GSP2), as the closest analogue.
Hi Eleni,
You can check the reference materials of IAEA-MEL with the code number IAEA-433 and another one with code number IAEA 405. It is intercomparison marine sediment used as reference materials for trace metals (which including Pb) and methyl mercury.
I recommend to compare your Pb results with many reference values to know exactly if the amount of Pb in your sediments samples is natural or due to anthropogenic contamination. You have to calculate the Anthropogenic Contamination Factor (CF) which compare your results with the the background concentration value of metal. Also there are another indices you can very easy check them in the references.
In my work, I used the background Pb value in sediments as referenced by McLennan (2001) for Pb as 17 ppm and used the world average as 10.15 ppm. In references you can find different levels in Pb in different locations in the Mediterranean sediments.
Good Luck
Hello Ayman,
The sediments you mention are already used every time we determine total Pb concentration in marine sediments and we actually have great recoveries of them. We have also participated to the latest IAEA interlaboratory comparison with the reference IAEA 458 so we use that too now. I do estimate Enrichment Factor because my cores are 30cm deep and the deepest sediment does represent the backround concentration (this is even proved with 210Pb analysis). But the IAEA 433, 405 and 458 do not have a certified Pb isotopes ratio
I have been able to answer my question, so I would like to inform anyone that would have the same question in the future. After an extent literature review I have found that the reference materials BCR-2 and AVG-2 of U.S Geological Survey are appropriate references for the determination of Pb ratios in environmental sedimets. We have purchased the BCR-2 SRM and we are pleased to see that it can be easily digested by our method.
One word of warning: most of the USGS standards have nugget contamination that affects the Pb isotope ratios. So don't panic if one in ten standard analyses come out wrong!
Dear Marlina
Your comment refers to the BCR-2G product which is the glass of melted BCR-2. The nugget contamination is only at the first one of course.
Actually, the nuggets seem to be present in the powdered SRMs, and they are a result of the industrial-scale crushing and milling that was done to obtain this large amount of SRM. It's not just me who found problems with this, there is also a paper by Dominique Weiss demonstrating this.
Dear Marlina
Thank you very much for the information. It seemed I was lucky enough cause the product we purchased gave good results (with the accuracy that the ICPQMS allows).
- Badges
- Science topic
- Similar topics
- Geoscience
- Atmospheric Sciences
- Atmosphere
- Air