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binbin
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Test for Lead in Alcohol
What would be the best way to perform a test for lead in ethanol with great accuracy?
Thanks,
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Zephyr
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To properly answer your question we need some more information.
How accurately?
Quantitatively?
How much are you willing to spend?
which concentrations will it be in?
I recently made some potassium rhodizonate which can be used qualitatively to test for lead...
If its as a salt in large concentrations then you could try and precipitate it and weigh it I guess.
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binbin
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Well, as accurately as possible within $50 or so. In the end, i'd just like to see if lead is being leached from brass fittings. So a simple, yes
lead, or no lead test would be great. But it would also be good to perform a titration to see exactly how much lead is in an alcohol solution.
The "great accuracy" was meant more of a, "it would be cool if.." but in the end, I'd just like to see if there is lead, or not.
[Edited on 4-7-2015 by binbin]
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aga
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http://www.docbrown.info/page13/ChemicalTests/ChemicalTestsc...
http://community.boredofstudies.org/241/chemical-monitoring-...
"generally you add Hydrochloric acid to a solution of cations. If a white precipitate forms (this is lead chloride), then lead ions are present.
Judging by your question, i think you mean an additional test. To verify the lead ions, you cann add pottassium iodide and the lead ions will react
with the iodide ion forming lead iodide which is a yellow precipitate "
The reaction with HCl seems to take quite a while, and at least one other reference suggests leaving it overnight to react.
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kecskesajt
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Well,lead chloride has a solubility of 10.8g/L.So if 5g of lead chloride formed,it cannot be detected but it is poisonus.
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Boffis
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Pinkhippo's suggestion that you use potassium or sodium rhodizonate is probably the best test for lead. If you evaporate down say 10ml on a white
porcelain bowl you should be able to detect less than 0.1 microgram of lead. Lead gives a brownish purple precipitate and barium a reddish brown
precipitate. Several other metals also give precipitates but treatment of the precipitate with very dilute (0.01M) HCl decolourises the other
precipitates but turns the lead ppt to a beautiful intense violet and that of barium a crimson colour. I use this test test to not only detect Pb and
Ba but to estimate the ratio of the of these metals present in minerals.
Other reagents include gallocyanine which can also be prepared easily if you have access to dimethylaniline.
@ Pinkhippo do you think it would be worth starting a thread dedicated just to the preparation and use of this type of microchemical reagent?
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blogfast25
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Much simpler and more widely used than rhodizonate is simply PbS (black and very insoluble). Also PbCrO4 (yellow and very insoluble).
If you're going to concentrate the lead by evaporating off the alcohol, these tests are good enough.
On lead detection as PbS, there's a very good Utoob somewhere.
K Rhodizonate by Nurdrage:
https://www.youtube.com/watch?v=BLmycZ2nrt0
[Edited on 4-7-2015 by blogfast25]
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AJKOER
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Here is a published work out of Nigeria testing local wine/fermented berry drinks. Link: [Edit corrected] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4256578/
The wines are subject to HNO3/H2O2 pre testing to determine levels of heavy metals.
I think this work can be of use not only for the procedures employed, but also provides some data on a particular locale heavy metal levels for
comparison to your sample.
Also, there is possible a statistical regression relationship between soil levels of heavy metals and your drink contents, or at least, a good
testable proposition.
[Edited on 5-7-2015 by AJKOER]
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kecskesajt
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Quote: Originally posted by AJKOER  | Here is a published work out of Nigeria testing local wine/fermented berry drinks. Link: http://www.sciencemadness.org/talk/viewthread.php?tid=62922
The wines are subject to HNO3/H2O2 pre testing to determine levels of heavy metals.
I think this work can be of use not only for the procedures employed, but also provides some data on a particular locale heavy metal levels for
comparison to your sample.
Also, there is possible a statistical regression relationship between soil levels of heavy metals and your drink contents, or at least, a good
testable proposition.
[Edited on 4-7-2015 by AJKOER] |
Wrong link.
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Boffis
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@Blogfast H2S is is very sensitive test but it is not very specific since about a quarter of the metals in the periodic table form insoluble
sulphides. The chromate test is more specific but less sensitive and calcium also forms a yellow ppt and there could be a lot more calcium around than
lead. To prevent interference for calcium (and Sr, Ba etc ) careful buffering is required.
Hydrogen sulphide is merely a collection reagent for groups of metals.
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binbin
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I checked out Nurdrage's video. However he mentioned at the end of the lead check video that in some instances, even products he knew contained lead
did not turn color upon contact. To be 100% sure, then use a professional kit or lab.
What about something like this? http://www.firstalert.com/battery/65-environmental/1033-diy-...
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blogfast25
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| Quote: Originally posted by Boffis | @Blogfast H2S is is very sensitive test but it is not very specific since about a quarter of the metals in the periodic table form insoluble
sulphides. The chromate test is more specific but less sensitive and calcium also forms a yellow ppt and there could be a lot more calcium around than
lead. To prevent interference for calcium (and Sr, Ba etc ) careful buffering is required.
Hydrogen sulphide is merely a collection reagent for groups of metals. |
Since as we're looking at brass, you'd only need to buffer against zinc, leaving on possible confusion between Cu and Pb. Which is where a chromate
test could come in handy.
Rhodizonate isn't perfect either.
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WGTR
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Anodic Stripping Voltammetry for Trace Lead Detection
A more complicated solution, but if the application is important, then there are labs that run these types of tests.
Attachment: PDF-23-Experiment5.pdf (180kB)
This file has been downloaded 527 times
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blogfast25
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| Quote: Originally posted by WGTR | A more complicated solution, but if the application is important, then there are labs that run these types of tests.
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That method is for watery solutions. The alcohol would at least have to be diluted somewhat.
Reminds me of polarography: halcyon days.
[Edited on 4-7-2015 by blogfast25]
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aga
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Would i be a total Fool by asking if Pb always renders ions in water, or could there be undissolved Pb in the water ?
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Sulaiman
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shine a laser pen through the liquid
any suspended matter will be visible
Tyndall effect https://en.wikipedia.org/wiki/Tyndall_effect
e.g. https://www.youtube.com/watch?v=vIUiK-ef8Hs
[Edited on 4-7-2015 by Sulaiman]
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aga
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Lead is said to be quite Heavy as i recall ...
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Sulaiman
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give it a stir/shake before testing !
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aga
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So, if it's to get water tasting better, involving shake/stir then vacuum filtering ...
"Just do the shake-n-vac to get the freshness back ..."
Anyway, how would one do a test for particulate elemental Pb in water ?
HCl again ?
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blogfast25
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It will simply sink, forming sediment. Lead in water is Pb<sup>2+</sup>
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Zephyr
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| Quote: Originally posted by Boffis |
@ Pinkhippo do you think it would be worth starting a thread dedicated just to the preparation and use of this type of microchemical reagent?
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Yes that would be great if others want to experiment with similar tests, I know I would. It would be nice to collect a large array of similar tests so
in the event of a false positive/negative it could be crosschecked to establish greater accuracy.
I prepared mine with great success using Nurdrage's method.
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binbin
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On the distilling forums, there is a tale going around that if the brass fitting containing lead is in the lower part of the column, the lead will not
be carried up by the alcohol vapours to the condenser. However if the brass/lead issue is after the head of the column, the lead will continue on to
the distillate.
Any truth in this?
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macckone
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| Quote: Originally posted by binbin | On the distilling forums, there is a tale going around that if the brass fitting containing lead is in the lower part of the column, the lead will not
be carried up by the alcohol vapours to the condenser. However if the brass/lead issue is after the head of the column, the lead will continue on to
the distillate.
Any truth in this?
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Lead is non-volatile so it won't distill but you could get small amounts of carry-over however if it is dissolved in the solution on the condenser
side it will flow down. However the amount of lead in brass is usually small and the amount dissolved is even smaller. Newer brass for drinking water
systems is lead free in the US.
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subsecret
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Depending on how much you drink, you might still sustain damage even if you can't see a rhodizonate/sulfide/chromate precipitate. Soluble lead doesn't
leave the body easily, and small amounts can build up over time. You'd need something better than precipitation to analyse those small amounts of
lead. Lead-free brass is the way to go.
Fear is what you get when caution wasn't enough.
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binbin
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| Quote: Originally posted by subsecret | | Depending on how much you drink, you might still sustain damage even if you can't see a rhodizonate/sulfide/chromate precipitate. Soluble lead doesn't
leave the body easily, and small amounts can build up over time. You'd need something better than precipitation to analyse those small amounts of
lead. Lead-free brass is the way to go. |
Or no brass at all. Raw copper can be found still, it'll be more expensive and harder to find for some parts, but can be found. To be considered
lead free, brass only needs to contain less than 0.25% lead, which is still not 0%.
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