My graphs always look like picture 2, while I need something like picture 1. I've read a lot on chronoamp, but none explains how to relate the two graphs together. I need the current vs. time graph but in a staircase like. I've run the CV and defined what are the voltage ranges for oxidation peak and that's what I'm putting in the parameters for my chronoamp.
Thank you.
Dear Maedeh,
Since you've told you're using CH instruments there are two chronoamperometry techniques are there: 1. Chronoamperometry 2. Amperometry i-t curve.
If you use the first technique you'll get the plot as in your first case but if you use the second technique you'll get the staircase response by a simple tweak in the experimental procedure as Joshua suggested (you've to add different conc. of analyte for a fixed interval of time).
For example, if you want to get a staircase response for your system with concentration range 1-100 mM, you've to add some x micro litre aliquot for say each y sec. (In your second graph they've added 0.1 mM analyte for each 100 sec).
In that technique (Amperometry i-t curve) you've to fix a potential and you've to give a long run time (say 10 steps of 100 sec interval amounts to 1000 sec run time. You can give say 1500 sec in case you get a response even after 1000 sec). Then once you start the experiment you've to pause the experiment after 100 sec. Then you've to add the analyte then you've to release the pause icon (not the start icon). For the second addition you've to pause at 200 sec and then you've to add. Then the experiment has to be terminated once a non-steady state response arises.
These parameters (potential, sample addition interval, etc.,) have to be optimized before you get a staircase response like the one you've shown in your second graph.
Hope this answer helps you.
Regards.
the results are deriven from a software connected to the electrochemical cell. I can't extract data and turn it into a staircase I guess.
Thank you though.
To plot a graph like picture 1, you must maintain the potential (only one chronoamperometric pulse) and add known amounts of your active substance, when a new steady state is reached. The steps in picture 1 are due to the increase of your active substance (the inset graph in picture 1 is the response current (at the steady state) vs the total amount (concentration) of your active substance at that moment).
Dear Emma,
Thank you so much for your suggestion. I understand that the steps are as a result of adding new concentrations of the substance, however the system I'm working with doesn't give me a step (staircase) like graph. It's more like a pals graph. all the step ones I see in literature are Current vs. time too, however, i don't know how they established such graphs.
CH Instruments only gives a pals like one and I don't know the transfer process. I also extracted the data given as Waldemar suggested and tries to change the graph in excel, however, that doesn't give me a staircase either.
Would you mind explaining more on developing the staircase graph?
Your help and time is greatly appreciated.
picture one looks like a double step chronoamperometry experiment. The "step" you see in that one isn't from concentration but a second potential (different from the initial potential) applied to the system and is related to chronocoulometry experiements. These are diffusion controlled and should be run quiescent.
The second picture is chronoamperometry where the potential is held constant and current measured over time, once a stead state is reached you inject your analyte and watch the current response. Subsequent analyte injections give the stair case response. In order to maintain a current response you need a stirred solution here.
For Epislon systems I believe you can just select "File" then "Save as" and select .txt. to export, then open in some sort of other software such as excel. There should also be some processing capabilities and a PDF output for the program as well. I may be a bit off here, it's been a while since I've used it and I'm pulling from memory.
Good Luck!
-Josh
Dear Joshua,
Thank you for your explanation. I'm trying to develop the second picture which is a chronoamperometry, but I get the first one. However, one error I noticed is probably my waiting time, which is in milliseconds, versos if I want to get the staircase graph I should titrate the solution over 30 minutes to an hour. Thank you for your info. I will try to get the staircase via the way explained.
Data extraction is not a problem, the development of the staircase graph is a challenge.
Thank you again. Please let me know of your further thoughts.
Oh, I see. It's not called chronoamperometry, I believe it's called "single potential time step"? Again from memory.
The one with the staircase shape? is that the "single potential time step"? cause I have such a feature in my software, if that is it, I can run the same properties under that technique.
Again, I'm not 100% sure of the name, but its not called chronoamperometry I'm sure of that. It might also be called "DC potential amperometry"
Good Luck!
Dear Maedeh,
Since you've told you're using CH instruments there are two chronoamperometry techniques are there: 1. Chronoamperometry 2. Amperometry i-t curve.
If you use the first technique you'll get the plot as in your first case but if you use the second technique you'll get the staircase response by a simple tweak in the experimental procedure as Joshua suggested (you've to add different conc. of analyte for a fixed interval of time).
For example, if you want to get a staircase response for your system with concentration range 1-100 mM, you've to add some x micro litre aliquot for say each y sec. (In your second graph they've added 0.1 mM analyte for each 100 sec).
In that technique (Amperometry i-t curve) you've to fix a potential and you've to give a long run time (say 10 steps of 100 sec interval amounts to 1000 sec run time. You can give say 1500 sec in case you get a response even after 1000 sec). Then once you start the experiment you've to pause the experiment after 100 sec. Then you've to add the analyte then you've to release the pause icon (not the start icon). For the second addition you've to pause at 200 sec and then you've to add. Then the experiment has to be terminated once a non-steady state response arises.
These parameters (potential, sample addition interval, etc.,) have to be optimized before you get a staircase response like the one you've shown in your second graph.
Hope this answer helps you.
Regards.
That's excellent. Thank you soooo very much Aravindan.
I will run an experiment as you've mentioned under the different technique today. Thank you again. I hope it works as you suggested.
Aravindan,
your technique worked and was highly useful. I appreciate the time you put for guiding me and just wanted to say thank you.
Regards,
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