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Liquid junction potential

Important: an analogous project has been developed using C#: https://github.com/swharden/JLJP

The liquid junction potential develops when two solutions with different concentrations
of ions come into contact.

Jljp is a program that allows the calculation of the potential, with an
arbitrary number of ions. It is possible to define the activity, as a
function of the ion concentrations.

Jljp is completely free and open source. It is the only free program
for the calculation of liquid junction potentials, working without any
limitation in the number of ions. Moreover it is the only program
available as open source.

Usually the Henderson method is employed in commercial programs. They
are often used for correcting the results of biophisical measurements.
The algorithm that we use is more general. The full description
of the method is available at arxiv.org/abs/1403.3640 .

Jljp is written in Java. The source files are freely availabe.
The classes are fully documented. It is possible to use the classes
directly in a Java program, or use them in other programs. Moreover,
a graphical panel and an applet, with full features, are also
provided.

http://jljp.sourceforge.net/index.html Go to the Project webpage

http://jljp.sourceforge.net/page.html Download and execute the program

Installation

The program requires Java, and the JSci package, also available as a Sourceforge project.

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 Example.java) and a graphical interface:
run Jljp.class.

http://jljp.sourceforge.net/doc/index.html Go to the Java API

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 automatically calculated 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 resulting voltage is displayed in the corresponding text field. It is also
possible to send a table with the concentrations of the ions, along
the liquid junction, to a desired PrintStram.

Mathematical formulation

See http://arxiv.org/abs/1403.3640 .