[chickapow]

Hey guys,

I'm new here so apologies if I break any (Read: all) of your rules with this post.

As part of my chemistry course this year at school I am undertaking a self directed project, which I have chosen to do about the lead content of soil found around the base of electricity pylons.

Long story short, I will extract metal ions from a soil solution using Modified Morgan's Solution (my method for this can be found on page 44 of [this](http://extension.udel.edu/lawngarden/files/2012/10/CHAP5.pdf) article), but I need to isolate all Lead compounds from a solution that will contain, not only lead in different forms, but hundreds of other metal compounds.

So far my best bet has been this; http://www.google.co.uk/patents/US7998440 however after preliminary classroom tests (done using solutions of a known quantity of Lead Nitrate solution) I am not hopeful of this being satisfactory.

Does anyone work in the field of soil chemistry, pardon the pun, and/or would be willing to offer any advice as to a cheap and relatively simple method of isolation?

[Borek]

Why this particular combination of extraction and precipitation?

I would start with some book on analytical chemistry - like Vogel's Quantitative Chemical Analysis or Dean's Analytical Chemistry Handbook - to find the best method.

Please note you are most likely working with traces, which typically means classic methods are useless, electrochemistry or spectroscopy are a way to go.

[chickapow]

Please note you are most likely working with traces, which typically means classic methods are useless, electrochemistry or spectroscopy are a way to go.

Oh, I absolutely understand that, which is why I'm not going for something like a titration (among other reasons).

The processes detailed above are to prepare a sample for spectroscopy which, as you know, will require the lead to be in one form.

Getting the lead into one form isn't the hard part though, it's isolating it that is.

[Borek]

Good spectroscopic method shouldn't require isolation. Or at least not in the form of the precipitate. There is no such things as "completely insoluble", so during precipitation always part of the substance is lost. When dealing with classic size samples (tenths of a gram) that's usually not a problem, when dealing with traces (starting around μg range) loses are unacceptable. The less operations you do, the better the final result.

[chickapow]

Good spectroscopic method shouldn't require isolation.

I agree with what you say but 'good spectroscopic method' isn't applicable at my school. When my output from the analysis will be a number from a seven segment display that I have to compare to a calibration curve I've made up earlier, it would be ridiculous to just plonk my base solution in.

Furthermore, losing accuracy through procedure is more favorable than through lack of procedure.

[chickapow]

I apologise for not specifying my situation before, there isn't too much in the way of precision analysis in my school.

[Arkcon]

Furthermore, losing accuracy through procedure is more favorable than through lack of procedure.

I'd like to hear you justify this statement, it really would help us understand what your needs really are, and might help you better understand what your project is meant to determine, and what limitations you will accept.  Deliberately causing loss of accuracy just seems wrong, on the face of it.  And "lack of procedure" which preserves accuracy, seems preferable.  Or you're just going to have to come up with a cogent explanation for why you need to do it your way.

You will need to do more research on procedures, there are many more in this world for just the task you have in mind.  You've quoted a patent, maybe that's the best Google result, but that's in no way appropriate for a high school project.  Patents are deliberately made complex and obfuscated, so they cover everything, and aren't easily copied.  You're not going to be able to use that procedure.

[chickapow]

Or you're just going to have to come up with a cogent explanation for why you need to do it your way.

Ok let me have a stab at it. As part of the write up for my project I'll have to do an evaluation about my limitations, where I could've done better etc.

The way I see it, leaving the rest if the metal ions in will produce more inaccuracy (from unclear spectroscope readings) than by attempting to make the solution as homogenous as possible.

I will accept any limitations, as long as I can talk about them in the evaluation at the end. Some of the best projects produced by our school (which are admittedly relatively low scoring) are mostly made up of improvements (Read: complaints) for their method.

[Arkcon]

OK, it seems you're married to a gravimetric precipitation, followed by spectroscopy, assay for lead in soil.  You said you tried something with lead nitrate in the classroom.  What did you get?  Can you try the same experiment with lead and other metal salts, and see how it works?  Can you get the sensitivity you need?  That is, can you see lead in av soil sample spiked with a very small amount of lead?  Do you get acceptable resolution?  Does 10,pmm., 50 ppm, 100 pmm all look the same?  And what happens with lead and iron mixed?  Lead copper and iron?  Lead, zinc and copper?