Lactic acid vs lactate in sweat

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In summary, the conversation discusses the use of artificial sweat for measuring the pH in order to estimate the anaerobic threshold by detecting lactic acid. The use of lactic acid in artificial sweat is explained and the potential of using copper-zinc electrodes for measuring pH is suggested. The conversation also touches on the pKa of lactic acid and the Henderson-Hasselbalch equation, as well as the use of Nernst equation for half-cell potential. The speaker encourages the person to learn more about these concepts on their own and come back with specific questions.
  • #1
juanfhj
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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.
 
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  • #2
juanfhj said:
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
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
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.
 
  • #5


I would like to clarify the difference between lactic acid and lactate in sweat and their roles in estimating the anaerobic threshold. Lactic acid is a molecule produced during anaerobic metabolism, while lactate is the deprotonated form of lactic acid. In other words, lactic acid is converted to lactate in the body, and it is lactate that is present in sweat. Therefore, when measuring the pH of sweat to estimate the anaerobic threshold, it is actually the lactate concentration that is being measured, not lactic acid.

The article provided does mention the use of lactic acid in the synthesis of artificial sweat, but this is likely for standardization purposes and does not reflect the composition of natural sweat. It is important to note that the concentration of lactate in sweat can vary based on individual factors such as fitness level and diet.

Regarding the use of copper-zinc electrodes to measure the pH of sweat, this method may work but it is important to consider the potential interference from other ions present in sweat. Additionally, the accuracy and reliability of this method may be affected by factors such as temperature and humidity. It may be beneficial to use a more specialized and validated device for measuring sweat pH in order to obtain more accurate results.

In conclusion, while lactic acid and lactate are related molecules, it is lactate that is present in sweat and plays a role in estimating the anaerobic threshold. Careful consideration should be taken when choosing a method for measuring sweat pH in order to obtain accurate and reliable results.
 

Related to Lactic acid vs lactate in sweat

1. What is the difference between lactic acid and lactate in sweat?

Lactic acid and lactate are often used interchangeably, but they are actually two different forms of the same compound. Lactic acid is the protonated form of lactate, meaning it has an extra hydrogen ion. In sweat, lactate is the predominant form.

2. Why is lactate present in sweat?

Lactate is produced in the body during intense exercise as a byproduct of anaerobic metabolism. This means that when the body is working at a high intensity and cannot get enough oxygen to the muscles, it breaks down glucose for energy and produces lactate as a byproduct. This lactate is then released through sweat.

3. What is the purpose of lactate in sweat?

Lactate in sweat helps regulate the body's pH balance. During exercise, the body produces more hydrogen ions, which can make the body more acidic. Lactate acts as a buffer, helping to neutralize these excess hydrogen ions and maintain a more balanced pH level.

4. Is the presence of lactate in sweat a sign of lactic acidosis?

No, the presence of lactate in sweat is not a sign of lactic acidosis. Lactic acidosis is a medical condition where there is an abnormal buildup of lactic acid in the body. This can be caused by a variety of factors, including certain medications or underlying health conditions. The amount of lactate released in sweat during exercise is not enough to cause lactic acidosis.

5. Can measuring lactate in sweat be used as a measure of fitness?

Measuring lactate levels in sweat can be used as a way to monitor training and fitness levels. As lactate levels tend to increase with higher intensity exercise, monitoring lactate levels in sweat can help determine an individual's lactate threshold, which is the point at which the body switches from aerobic to anaerobic metabolism. This information can be used to tailor training programs and improve athletic performance.

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