Calculation of the liquid junction potential

Click here for downloading the program.

Home page of liquid junction potential calculator

Quick start!

Run the jar. A graphical interface will open. Do the following operations.
  1. Write "Na" in the "Ion name" text field.
  2. Press "Add" button.
  3. Write "Cl" in the "Ion name" text field.
  4. Press "Add" button.
  5. Check the radiobutton under the column "X" in the row "Na".
  6. Check the rediobutton under the column "Last" in the row "Cl".
  7. Write 1 in the column c0 of the row "Na".
  8. Write 3 in the column cL of the row "Na".
  9. Press "Calculate".

The program calculates the voltage across the liquid junction between two NaCl solutions, at 1 and 3 M.

Using the program

The package can be used both as single classes (see and a graphical interface: run Jljp.class.
First of all, the ions must be added. In the graphical panel, put the name of the ion in the text field, and press "Add". Please use names like "Na", "Cl". Do not put the charge. For ions that can have various charges, use e.g. FeII and FeIII. If possible, avoid numbers.
For each ion, seven parameters must be defined.
  1. Name: e.g. Na, Zn, Cl.
  2. Charge (relative to e): e.g. 1 for sodium, 2 for zinc, -1 for chlorine.
  3. Mobility, in m/s / N (not the electrokinetic mobility!)
  4. cdadc: see below.
  5. c0 (M): concentration at one end of the interface.
  6. cL (M): concentration at the other end of the interface.
For some common ions, the program automatically fills in the correct values of charge and mobility.
The parameter phi is the flux of the ion. Only the relative value matters. It is calculated automatically by the program.
The parameter cdadc is c*d ln a/dc, i.e. the derivative of the logarithm of the activity with respect to the concentration, multiplied by the concentration. The units of "c" and "a" are M, mole/liter. The quantity c d ln a/dc is dimensionless. In the approximation of small concentrations, the activities are close to the concentrations, and c d ln a/dc is approximately 1. It is possible to put any formula in this field, depending on the concentrations of the ions, e.g. : "3*tan(Na/Cl)".
It is necessary to define two ions as "x" and "last". The values of c0 and cL for the ion "last", provided by the user, are neglected, and calculated from the values of the other ions, by imposing the electro-neutrality. The concentration of the ion marked as "x" is used as a spatial coordinate, over which the numerical integration takes place. The choice of the "x" ion should not affect the results. See the paper for further details.
The resulting voltage is displayed in the corresponding text field.