Chronopotentiometry

Definition of chrono potentiometry
Introduction about chrono potentiomerty
Experimental setup of chronopotentiometry
Theory of chronopotentiometry
Output wave function of chrono potentiometry
Analysis of an chronopotentiometry
Main window of chronopotentiometry
used files in chronopotentiometry
disadvantages of chronopotentiometry
Application of chrono potentiometry
compare of chronopotentiometry
Using hardware
Feature of files in chronopotentiometry

1. chronopotentiometry Done by K. Revathi I-M.sc Chemistry

2. Introduction… Stationary electrode Unstirred = mass transport by diffusion Constant current applied between electrodes Measure potential vs time

3. Introduction Chronopotentiometry is useful for investigation of electroporation phenomenon of bilayer lipid membranes. The measurements are provided in current-clamp conditions. This technique allows to obtain only simple pore in the membrane. The pore has size about few nano meters - size similar to the membrane thickness. The pores are stable or irregular oscillating.

4. Theory of Chronopotentiometry A gradual change in E occurs as [Red] goes up and [Ox] goes down (transition region) Ultimately the surface concentration of Ox goes to zero & to sustain the constant current applied, electrode potential makes a rapid change to the value required to make a new process go

5. Chronopotentiometry Output Wave E time Tra n sition Time ( τ ) At start no Red is present so E is not defined Point at which Ox is used up

6. Hardware The program controls the KSP measurement system with following modules:  DPTG-461 - programmable potentiostat - galvanostat ADC-1204 – analog – to - digital convereter . DAC-1201 - digital-to- analog convereter . TIMER-49 - programmable timer  Measurements are made in a four-electrode arrangement

7. Features of the program   saving of data and printing of the report. writing of data as a text file for using in worksheets and graphic programs. selection 2-, 3- or 4-electrode system. setting up to 10 methods (sets of measurement parameters and experiment descriptions). readout of data directly from the graph. readout of curve slope directly from the graph. zoom of the graph.

8. Main window of the "Chronopotentiometry" program . The curve shows electroporation of the bilayer lipid membrane made from egg yolk lecithin. The begin increasing of the potential is for the membrane without pores. Membrane voltage increased with speed dependent on current intensity, membrane capacitance and membrane resistance. When voltage attains to the breakdown voltage value the membrane resistance rapidly decreases causing decreasing of voltage on the membrane. Size of the pore irregular oscillates and membrane potential changes. There is an irreversible breakdown of the membrane. The generated pore is full filled by the electrolyte. Disconnecting of the current flowing causes closing of the pore and recovering of uniform structure of the membrane in time of seconds to minutes.

9. Used files CHRONPOT.EXE - main program file CHRONPOT.INI - configuration file CHRONPOT.HLP - help file  DPTG.DLL - driver for the potentiostat / galvanostat module ADC.DLL - driver for the analog -to-digital converter module DAC.DLL - driver for the digital-to- analog converter module TIMER.DLL - driver for the programmable timer module

10. Application of chrono potentiometric measurements   studies of membrane electroporation phenomenon. studies of membrane transport processes. studies of basic properties of membranes as capacitance and resistance.

11. Summary In reality it is better done by other methods. Chronopotentiometry illustrates constant current situation in electrochemistry. Chronopotentiometry is very poor at handling capacitive current.

12. Reference   1. S. Kalinowski and Z. Figaszewski, A four-electrode potentiostat-galvanostat for studies of bilayer lipid membranes,  Meas. Sci. Technol. ,  6  (1995) 1050-1056. 2. S. Kalinowski, G. Ibron, K. Bryl and Z. Figaszewski, Chrono potentiometric studies of electroporation of bilayer lipid membranes,  Biochim. Biophys. Acta , in press (1998).

13. Thank you friends ..