This program fits data to the equations:-
Alkaline sigmoid
kobs = k/(1+[H]/Ka)
Acid sigmoid
kobs = k/(1+Ka/[H]

When "Fit" is selected a linear reciprocal plot is used to make the initial estimates of kobs and the pKa. These values of kobs and pKa are then used as the initial estimates to fit the experimental data using an iterative, non linear least-squares regression program.
When "Fit with estimates" is selected you must input the initial estimates of kobs and the pKa. The experimental data is then fitted using an iterative, non linear least-squares regression program.
Results can be printed, saved as a text document or copied and pasted into other applications such as Word.
Instructions and test data are provided.