Ok -- how does this work and can we DIY this?
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Ok -- how does this work and can we DIY this?
It is possible to recreate. This particular kit looks like it uses sodium rhodizonate. However all that is necessary is something that reacts with lead to make a colorful, insoluble precipitate
The following article details some of the chemistry and chemicals involved, and refers to a lab book that is very good that also has a lab based on the same topic: http://makezine.com/laboratory-198-analysis-of-paint-sa/
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I wonder how reliable these test strips are for lead; I've heard that some of the less expensive colorimetric techniques like this are pretty unreliable when assessing arsenic and mercury levels. Then again, even if this method isn't great at providing absolute concentrations, it might still work well as e.g. a binary indicator ('some of contaminant X is present' or 'there is no contaminant X present') ...
Wow, mrericsully - interesting. Is sodium rhodizonate toxic itself? Could any be obtained easily and safely to make such strips ourselves?
I also like the use of white vinegar for dissolving lead that may be in soil or dust.
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The sodium rhodizonat isn't toxic according to the SDS I just looked at. The cost of the chemical itself might be a little prohibitive, but searching for it I stumbled across a YouTube video on making a related chemical potassium rhodizinate, which would do the same thing, since it is the rhodizinate anion that is important for the reaction and not the alkali metal cation: https://www.youtube.com/watch?v=BLmycZ2nrt0 .
There are of course, other colored lead precipitates which although they'd probably be more cost effective and/or easier to obtain.
Hi Don - why would they be unreliable; false positives? Poor calibration? Any links I could read up on?
Howdy --- This thread is a bit old but it's left unresolved. I have a little experience in this space, both in my playing with these lead testing strips and also talking to others that have. The overall consensus is that... they're no good and should be avoided. But...
// COULD they be used? Maybe, if your goal is to determine that a water is not super high in lead count, then I could see a role for these. My sense is that you'd want to do at least 3 strips with the same water sample. If they all show up exactly the same with a clear signal that there's "zero" lead or that there's "a lot of lead", then that could be a signal; any signal that shows a "non-zero".
// But these things are so hard to read. I'm putting zero in quotes because obviously there's not a true numeric reading. The strips I've tested have shown some amount of lead but not enough of a signal to provide any confidence either way.
// More formal research done by @smmontgom at https://docs.google.com/presentation/d/1tWOEIZ0yhNs9g3sK5bJtTwx7ldODiI5RVTMbwwwxxHw/edit#slide=id.p1 . Conclusions include "Strip results tend to under represent Pb level (for this specific study water). Also significant variability. Much more testing needed."
Sources / links. It all feels a bit insufficiently conclusive to me.
Store-Bought Lead Tests: Are They Worth It? Analysis of the top three home-testing kits at Home Depot. (They're mostly frowned upon and paint a negative picture). --> https://mytapscore.com/blogs/tips-for-taps/store-bought-lead-tests-are-they-worth-it
"Marc Edwards is a professor at Virginia Tech who has tested water for lead in D.C. and Flint, Michigan. He is not a big fan of the home testing kits. If they are positive, he said, you can trust that result. But if it's negative, you still don't know for sure." --> https://wjla.com/features/7-on-your-side/testing-for-lead-in-your-water-are-home-tests-reliable
Customer Reports, in this "how to test for lead" post, noticeably doesn't explicit mention these strips, but does seem to suggest that they might be useful (maybe). Pretty unclear... They do link to the strips via the Buy on Amazon link at the bottom so maybe that means they're cool with them in at least certain situations? --> https://www.consumerreports.org/cro/lead-test-kits/buying-guide/index.htm
These kits sold on amazon have mixed reviews, for what that's worth.
The problem is the dilute vinegar they provide won't penetrate all materials ( i.e. Not all kinds of paint, not all kinds of plastic, etc.). So you can't be sure you are dissolving all lead present.
There are ways around this, but they aren't easy. That's the base issue.
@bronwen do you have a contact with Franciska from the Barnraising who might be able to chime in on this thread?
@warren I do, but she's a little off the grid at the moment. She said she'd be able to get back into this in the fall!
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