Lactic acid vs lactate in sweat

  • Thread starter juanfhj
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  • #1
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Main Question or Discussion Point

I want to measure the pH of sweat in order to estimate the anaerobic threshold by detection of lactic acid.

Many references point out that it's lactate, not lactic acid, that is found in sweat.

However, according to this article:

http://www.bentham.org/open/tocorrj/articles/V003/38TOCORRJ.pdf

Artificial sweat is synthesized with lactic acid as per standard ISO 3160-2, (20g/l NaCl,
17.5 g/l NH 4 Cl, 5g/l acetic acid and 15 g/l d,l lactic acid with the pH adjusted to 4.7 by NaOH).

Also, I want to measure the pH by the potential sensed by copper-zinc electrodes in series etched on a PCB. Would that work?

Thanks.
 

Answers and Replies

  • #2
Borek
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Artificial sweat is synthesized with lactic acid as per standard ISO 3160-2, (20g/l NaCl,
17.5 g/l NH 4 Cl, 5g/l acetic acid and 15 g/l d,l lactic acid with the pH adjusted to 4.7 by NaOH).
What is pKa of lactic acid? Do you know how to calculate concentration of lactate and lactic acid knowing pH and pka?

Hint: Henderson-Hasselbalch equation.

You will be not able to find lactate/lactic acid concentrations measuring pH.
 
  • #3
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I get it. Another question: what information could a half-cell using sweat as the acid (Nernst equation) give about the sweat properties? I'm not really familiar with reduction potentials, chemical activities of reductants and oxidants, and their relation to pH. Also, I don't understand if the Nernst equation applies to the lemon battery, in which I don't see an apparent salt bridge.
 
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  • #4
Borek
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Seems to me like you are struggling with the general chemistry, not with the biological aspects of your problem.

Nernst equation describes any half cell. Half cell potential can be a function of pH, can be not. Sorry, but this is not a place for a full lecture on the Nernst equation, I suggest you learn about things you have listed (and looks like they are crucial for what you are trying to do) on your own, they are explained in many general and analytical chemistry books. Come back with specific questions.
 

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