My greenhouse experiment will be concluding soon and I'll be ready to harvest my plant tissues to test for lead, cadmium, and arsenic. I've found a couple different papers giving a vague overview of how they prepared and tested their samples and one that has a pretty decent description of their method, but I wanted to see if any researchers here had a well established protocol (for the whole process from drying out the harvest tissue to digestion. Once it's digested and in the standard solution, the procedure for the ICP-MS should be the same as for anything else.)
Thank you so much! This is my first research project, so I really want to do it well.
For mercury it is recommended using AAS or better cold vapor AAS. Kindly have also a look into that link:
http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/41/131/41131193.pdf
Ruediger B. Richter
Dear MS. Leo
The best method is to dry the sample and powder them to fines. I am sending you one of my published papers. It might be helpful to your work.
Truly yours
karbassi
In regard to to protocol suggested by H.G. Zha: The use of perchloric acid to digest plant materials has potential hazards. Reactions of perchloric acids and organic materials, including cellulose, are potentially explosive. Although aqueous solutions may be stable, spontaneous explosions may occur if samples are allowed to dry. Also, perchloric acid vapors may react with metal surfaces in fume hood ducts to produce explosive perchlorates; most lab fume hoods are not rated safe for use with perchloric acid.. For more information, see the attached MSDS sheet.
http://www.sciencelab.com/msds.php?msdsId=9926440
The combination of nitric acid and perchloric acid for wet ashing is pretty common, but there are hazards. I recall seeing a report of a lab explosion where filter papers that had been used to filter perchloric acid solution were placed in a 100 degree C drying oven. The warmth was sufficient to reach the critical explosion temperature, blowing the doors off the oven. For wet ashing, the greatest hazards may come during handling of the acid during preparatory steps (e.g., spills, or allowing the concentrated acid to come in contact with paper towels).
If you are considering this method, here is a detailed description:
http://www.nrcresearchpress.com/doi/pdfplus/10.4141/cjss88-041
A web search for "wet ashing plant tissue" will reveal some other possible methods. These include microwave digestion, use of nitric acid + hydrogen peroxide, etc.
Thank you all so much, this has been incredibly helpful! I'm so excited to get started, drying out my plant samples now!
Dear Elizabeth,
please be so kind and up-vote the answers of the colleagues, which were most helpful to you.
kind regards
Plant samples should be washed carefully just after sampling while they keep turgor and then dry to constant weight UNDER ROOM TEMPERATURE, especially because your are going to determine As.
For digestion I usually use just nitrice acid and micro-wave oven for short time and not so high temperature. And I do not cut my plant samples. Finally all samples will be transferred to liquid state. I am afraid you can have some problems with As. Dilute simultaneously standard reference material (plants of course) to see how accurately you could determine your elements.
By the way. Sorry, but selection of your elements are not very interesting. A lot of experiments were previously done on these so called heavy metals (As is metalloid but not metal).
Good luck.
Irina Shtangeeva: Can you explain the rationale for drying my materials at room temperature? Why would arsenic concentrations be affected by following an oven drying procedure? Additionally, what do you mean when you state "I do not cut my plant samples"? You mean you do not add any additional materials? I wasn't intending to. I do already have plant standards to test alongside my samples (I think this is noted in my research proposal on my profile, but I am not entirely sure).
As for your opinion that it is not very interesting, that is fine with me. I am an undergraduate researcher doing my first research project entirely on my own, mostly to understand HOW to design and accomplish research. Would you criticize an undergraduate student working in a professors lab doing "grunt work" on well studied materials or phenomena for working on something that is not very interesting? This was not intended to be ground-breaking research and there is in fact a group at John's Hopkins University that is doing a far more in depth study of heavy metal contamination in Baltimore's urban gardens. I understand your concern from the standpoint of advancing scientific understanding since my work is rather redundant. If you wish, think of my project as more of a preliminary study than work that would be thesis-level. I intend to do further research this Fall, after I've successfully completed this project and understand how to design my own experiment and generate useful and significant data.
Thank you for the response and well wishes!
OK. I performed my first work when I was student. The idea of the experiment was my own as well as elemental analyses (neutron activation analysis) I also conducted myself. But do not worry, and I wrote "sorry" as you see. You can of course do what do you want to do.
As to other.
Arsenic rather easy to lose under high temparature, is not it?
As to cutting plant samples. I usually do nothing with samples, just add acid. My opinion is that the less steps for sample treatment you do, the less analytical errors you have.
Irina Shtangeeva: What would be your recommendation for prepping a "wet" vegetable sample, such as a tomato fruit? Would you still recommend not using a drying oven to prevent loss of As? Thank you!
Yes, I think so. But you can check yourself using both procedures. Why not?
As to me, I try to exclude as many additional steps during sample pre-treatment as possible. Each such a step can lead to additional error.
And what would I do if I would decide to use tomato fruit... Probably(?) I would cut it and would try to dry on the paper till constant weight.
Good luck in any case!
I guess my post is outdated and I hope you had a good experiment. There are some established procedures that commercial analytical companies would use: just nitric digest, aqua regia on non ashed material or ashed material, but as long as you use appropriate reference material you can asses the quality of the results. This book might be of interest http://www.plantstress.com/methods/Handbook_of_Reference_Methods_for_Plant_Analysis%201998.pdf
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