Public Lab Research note

Arsenic detection with UV-Vis spectrometry

by warren |

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I was reading up on how to detect arsenic in soil, since the UMASS soil tests offered at such great low cost don't cover arsenic, yet that's one of the contaminants of concern here in Somerville, Massachusetts. I found this great thesis on using UV-Vis spectrometry (the kind we're trying to develop at PLOTS) with a kind of arsenic-binding dye (if I'm reading this right). Pretty dense, but offers some good leads for eventual lower-cost testing. Also a good quote here:

X-ray fluorescence spectroscopy is very well-suited for the analysis of soil samples since it provides a rapid analysis of multiple elements in a non-destructive manner. Portable X-ray fluorescence units are now available in a price range ($20k to $40k) that makes their inclusion in educational settings feasible. (also attached to this post)

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arsenic-uvvis-spectroscopy-ChristinePellegrini_HonorsThesis.pdf 747 KB 2011-09-26 19:18:52 +0000

spectrometer arsenic


Note that the above spike is not even in the UV range -- it's around the color green, which we could easily pick out with the basic spectrometers we have now.

Pasting in comments from the plots-waterquality list --

There's arsenic in some Somerville soil -- especially at the Kiley Barrel site right near Union Square, near the planned Green Line station: and at this bike path, according to the MASS DEP's flickr stream:

The low-cost soil tests offered by UMass Amherst's Soil Lab test for arsenic, for an extra $5 on top of their $55 Total Sorbed Metals Test:

I just read this article, though, which talks about extracting arsenic using sodium hydroxide (lye?) and phosphoric acid (a food additive), both easily purchased -- then igniting it into plasma and measuring its emission spectrum with a spectrometer.

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There are a few " killers" in the referenced article. One was the remark about converting arsenic to volatile hydrides. One of those hydrides could be a nasty gas ( arsine or arsenic trihydride). The other was the mention of the analytical technique of inductively coupled plasma (ICP). A very good technique but usually expensive.

I've been looking for a good, safe, method for arsenic analysis for a long time. Please keep looking for good methods.

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