For an experiment, I need to measure the amount of iron in a soil sample.
The approach is similar to that of a metal detector, but with a major difference; the iron is in form of powder and is distributed at a variable percentage in the whole sample.
The measurement must be indirect (no contact with the soil allowed), so I can only think it is a phenomenon related with EM fields, or an ultrasonic measurement system.
Ideally the system should estimate the percentage or iron powder, but a good start could be the measurement of changes in the concentration.
Any suggestions? Can you suggest other measurement methods? Do you think I am on the right track with EM or ultrasound?
Mössbauer spectroscopy or x-ray fluorescence should work, but there will be calibration work prior to be able to quantify the results.
Both methods will work for all compounds of iron. Downside the limited sensitivity
Regards
Marko
Maybe this approach is completely irrelevant for you, but have you thought about the LIBS method? Attaching a link to a sample paper on soil invetigation by LIBS: ftp://ftp.okcc.state.ok.us/CARBON%20PROGRAM/To%20SES,%20Inc/2003%20LIBS%20for%20measuring%20soil%20C%20-%20Soil%20Science%20Soc%20of%20America.pdf
We own a Thermo Niton XL3t handheld xrf analyser. It's doing a good job in the field, and it came shipped with a bulk mineral analysis and a soil heavy metal analysis methods. With respect to accuracy you must keep in mind that all typical restrictions in xrf analysis apply when the samples lack lab preparation: sample heterogeneity, texture, density, surface roughness etc. It is not a replacement for lab analysis. You may, however, take your samples to the lab and take all QC measures, which probably will improve the quality of the results.
As above, portable XRF is the way to go. It will not be able to determine between your added iron particles and the naturally occurring iron in the soil. For that you will need isotopic analysis which is only available at present by a destructive technique, soil digestion followed by ICP-MS analysis.
Magnetic susceptibility, the problem is that there is a grain size effect, you have in situ or lab equipment. If you have pur iron powder you can make a reference . In fact,this is EM measurment.
We have been working with a portable VNIR and it works for the majority of metals.
Dear Jose, we have a Phazir handheld NIR spectrometer and use it mostly for organic contaminants in soil (for example, see http://dx.doi.org/10.1007/s11270-012-1298-y). How did you calibrate your instrument for heavy metals? Regards Thomas
Thank you for all the answers written so far!
I think that spectrometers or X-fluorescence could be very good methods, but I don't think we have enough experience and know-how to use them.
A more suitable alternative could be using magnetic susceptibility as suggested by Mr. Francois. Measuring these phoenomena is at our reach.
you can rent portable x-ray spectrometers or ask a vendor, if you try one for a week to evaluate suitability. Sometimes the geology, chemisty or materials science department already have a portable or a lab x-ray fluorescence spectrometer you may use.
The magnetic methods will suffer from the wide range of magnetic properties iron compounds and metal have. Any metallic iron also also prone to oxidation and will rapidly change as will Iron(II) compounds. The size of the clusters of your iron will have an effect on the frequency if you work with AC methods.
I mean, give it a try, but I fear if you are more after the iron data than developing a measuring method, you may use more time than you would have to.
Nice read on such a magnetic method and how to interpret the data.
http://www.geo.uni-tuebingen.de/fileadmin/website/arbeitsbereich/zag/geomikrobiologie/downloads/Rijal_et_al_Haenigsen_StudiaGeophysicaGeodaetica-2011.pdf
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