Sr i think there is a mistake in the last step, the potential measured would be = K - (0,05916/n) * log(1/a(out)) or by log properties; = K + (0,05916/n) * log(a(out))
hey I have a few questions about the ion selective membrane on a microscopic scale. first of all: do the ions get through the membrane and end up in the internal solution? then a constant a(intern) would be impossible. And: diffusion would be defined by the difference in concentration of ALL Ions in external solution to the internal solution. So sometimes (if the overall concentration in the external solution is very high, all ions would diffuse through the membrane (f. e. valinomycine and K+) and if not, there will be an equilibrium before and diffusion would be stopped. so there is a big measure mistake. what am I getting wrong? In a glass membrane, Na+ is exchanged with H+, H+ does not get through the glass, the potential is only at the mebrane. that makes sense to me, because the glass is selective for H+ (and a small amount Na+). But how des this work with membranes which really let Ions through? or does an membrane never let any ions really diffuse through it and its like the SiO2 from glass, just oj the surface?
Great question. As far as I understand, the ions from the solution being analyzed do not diffuse through the membrane, instead a very small amount of the analyte ion diffuses from the membrane into the solution. The amount that diffuses is very small because a charge difference builds up on the surface of the membrane because the negative ions cannot diffuse from the membrane because they are hydrophobic. That charge difference is actually what the electrode is measuring, and depends on the concentration of ions in the solution (which is the principle of how these electrodes work). If the concentration of analyte (K+ in our example) was very high, it would indeed be able to enter the membrane instead of the ions coming from the membrane, and the electrode would not be a good way to measure K+ anymore. These electrodes have specific concentration ranges where they function best, so there probably is a sufficiently high K+ concentration that would prevent the electrode from working as intended. These limits are usually given by the manufacturer of the electrode.
@@jacobstewartchem Ah I think I understand. The membrane is saturated with K+ (or another ion), and is in equilibrium with the analyte. so depending on the K+ concentration in the analyte, some ions diffuse from membrane to analyte, the potential of the membrane alters proportional to it, and the sensor is calibrated, so a certain potential refers to an certain concentration in the analyte. that makes kind of sense. thank you very much. but I still don't fully understand it. ion selective electrodes can measure in mixtures of many ions (like blood). so why is the eqilibrium just regulated by a certain ion. osmotic pressure is regulated by all ions in the solution. so if the overall concentration is very high, I don't get why K+ should diffuse from membrane to analyte at all. or is the concentration in the membrane so high, that this is not possible? I am very confused haha. I just read the chapter in Harris- quantitive analysis. It kind of cancels everything in the nernst equation, and you are right, the potential is created by K+ diffusing out of the membrane. I just don't get why this diffusion is only K+ (bulk) dependent. because if the concentraton in the membrane is always higher then bulk, again osmotic pressure would regulate it, and osmotic pressure does not care about a certain ion. So ions would always diffuse out of the membrane... thank you for your answer.
Hello, this number comes from the Nernst equation, which is used to calculate potentials in electrochemistry. This particular value is a collection of constants assuming room temperature. You can find more in this video I made: ruclips.net/video/MLdKhWCejgA/видео.html
Sr i think there is a mistake in the last step, the potential measured would be = K - (0,05916/n) * log(1/a(out)) or by log properties; = K + (0,05916/n) * log(a(out))
thank you for the informative video!
You are very welcome, glad it could help!
Thank you a lot!
You are very welcome!
Thanks, nice explanation.
Thank u Sir for the wonderful explanation
Thankyou so much very helpful to me ❤
Glad it could help!
Please explain biosensors and third types bro my exam is soon and I need help. This video has helped just in one part of exam but we need ur help.
hey I have a few questions about the ion selective membrane on a microscopic scale.
first of all:
do the ions get through the membrane and end up in the internal solution? then a constant a(intern) would be impossible. And: diffusion would be defined by the difference in concentration of ALL Ions in external solution to the internal solution. So sometimes (if the overall concentration in the external solution is very high, all ions would diffuse through the membrane (f. e. valinomycine and K+) and if not, there will be an equilibrium before and diffusion would be stopped. so there is a big measure mistake. what am I getting wrong?
In a glass membrane, Na+ is exchanged with H+, H+ does not get through the glass, the potential is only at the mebrane. that makes sense to me, because the glass is selective for H+ (and a small amount Na+). But how des this work with membranes which really let Ions through? or does an membrane never let any ions really diffuse through it and its like the SiO2 from glass, just oj the surface?
Great question. As far as I understand, the ions from the solution being analyzed do not diffuse through the membrane, instead a very small amount of the analyte ion diffuses from the membrane into the solution. The amount that diffuses is very small because a charge difference builds up on the surface of the membrane because the negative ions cannot diffuse from the membrane because they are hydrophobic. That charge difference is actually what the electrode is measuring, and depends on the concentration of ions in the solution (which is the principle of how these electrodes work).
If the concentration of analyte (K+ in our example) was very high, it would indeed be able to enter the membrane instead of the ions coming from the membrane, and the electrode would not be a good way to measure K+ anymore. These electrodes have specific concentration ranges where they function best, so there probably is a sufficiently high K+ concentration that would prevent the electrode from working as intended. These limits are usually given by the manufacturer of the electrode.
@@jacobstewartchem Ah I think I understand. The membrane is saturated with K+ (or another ion), and is in equilibrium with the analyte. so depending on the K+ concentration in the analyte, some ions diffuse from membrane to analyte, the potential of the membrane alters proportional to it, and the sensor is calibrated, so a certain potential refers to an certain concentration in the analyte. that makes kind of sense. thank you very much. but I still don't fully understand it. ion selective electrodes can measure in mixtures of many ions (like blood). so why is the eqilibrium just regulated by a certain ion. osmotic pressure is regulated by all ions in the solution. so if the overall concentration is very high, I don't get why K+ should diffuse from membrane to analyte at all. or is the concentration in the membrane so high, that this is not possible? I am very confused haha.
I just read the chapter in Harris- quantitive analysis. It kind of cancels everything in the nernst equation, and you are right, the potential is created by K+ diffusing out of the membrane. I just don't get why this diffusion is only K+ (bulk) dependent. because if the concentraton in the membrane is always higher then bulk, again osmotic pressure would regulate it, and osmotic pressure does not care about a certain ion. So ions would always diffuse out of the membrane... thank you for your answer.
What does the 0.05916V refer to? I couldn't quite catch what Sir said
Hello, this number comes from the Nernst equation, which is used to calculate potentials in electrochemistry. This particular value is a collection of constants assuming room temperature. You can find more in this video I made: ruclips.net/video/MLdKhWCejgA/видео.html