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Public Lab Research note

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Pencil lead works well as an electrode material in lead analysis

by JSummers |

What I want to do

This was a test to see if pencil lead can be used as an electrode material in electrochemical lead analysis.

My attempt and results

I have a paper (Goldchamp, et al, J. Chem. Ed., 2008, 85, 976) that discusses using pencil leads as electrodes in the electrochemical determination of lead. Now, I have always relied on my fancy commercial electrodes made from something called "Glassy Carbon". The cost about $100 each, so they have to be better, right? Apparently not. The image above shows three voltammagrams. The big peak in the center shows the presence of lead. The green data set was acquired using my glassy carbon electrodes. The blue data set shows what you get using a 2H pencil lead (0.7 mm, Pentel, High Polymer, SUPER) as working electrode. The red data were acquired using pencil leads for both the working and counter electrodes. Note that the peaks obtained using the pencil leads are as sharp as that obtained using glassy carbon and the background is cleaner.
Now, I have tried using graphite sticks in the past and had problems with them. The paper referenced above says that you have to use hard pencil leads. Don't just use what ever is laying around the house. The assay is carried out in dilute nitric acid and I think it reacts with the softer lead materials. Just go out and find the 2H leads. I got mine from the internet.

Questions and next steps

So there are a few things that need to be done: 1. We need to devise a way to get a consistent surface area where the electrode contacts the solution. The signal is proportional to the surface area, so having the electrode half in the solution and half out will not work.
2. We need to get good concentration versus response data so that we can say that our method can measure lead at relevant concentrations. 3. We need to look at whether we can substitute bismuth for the mercury that is used in this analysis traditionally, so as to minimize the toxicity issues associated with the waste. 4. We need people in affected areas (like Flint, MI) who want to take action.

Why I'm interested

We need tools for citizens to measure lead in their water.

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potentiostat cheapstat tool open-water lead pencil

response:9932 activity:potentiostat


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