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Public Lab Research note

Sulfur, sodium detection in flame spectometer tests

by warren | November 20, 2012 20:36 20 Nov 20:36 | #4964 | #4964

At the Barnraising in Cocodrie a couple weeks ago, we had a hands-on session for spectrometer testing, and I brought some recent prototypes to try out. After the impressive tests by Stu in Australia last month, we were eager to try flame emission spectroscopy of soil samples, and Shannon and Liz brought some samples from New Orleans which would be likely to have some heavy metals in them. We ultimately didn't get to test those... but we did get some pretty good spectra of both sodium (prepared salt water, and marsh mud soaked in both water and vinegar) and sulfur (from matches). Above, Stewart Long and Dan Beavers and I burn things.

You can see some of the data here: https://spectralworkbench.org/spectra/search?q=lumcon

We tried using white vinegar to dissolve some copper from pennies, but it didn't seem to work -- granted, folks on the list had suggested stronger acids, but we just wanted to see if a more readily available, cheaper acid like vinegar would work. Some notes on vinegar which we jotted down:

  • vinegar didn't seem to be much different from water
  • its a really weak acid
  • the trick with etching pennies usually uses salt + vinegar, and Straylight/Stu says (and we showed) that salt overpowers most other spectra, so that may not work, maybe we really need a stronger acid
  • at the end of the day, none of the samples that we tested actually had even suspected heavy metals, so the fact that we didn't see much wasn't a surprise

Stu recommended evaporating a lot of the solvent (water) off to concentrate what we're able to soak out of the soil. Maybe we should try that... I'm going to look into where around Somerville MA I should collect likely lead- and arsenic- contaminated soil, since those are both issues around here.



Moderate strength hydrochloric is readily available (in the US) at hardware stores as "muriatic acid"

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hcl is a strong acid but it won't work with cooper unless you add hydrogen peroxide, so i would recommend nitric acid for dissolve samples

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