ProtoFit is a tool for optimization of surface protonation models from acid-base titration data. The software consists of two parts: ProtoFit, which is the program for model parameter optimization and simulation; and ProtoFit-GUI, a graphical user interface to ProtoFit with data and model visualization capabilities. ProtoFit-GUI provides for easy simulation of titrations and graphical comparison of model with measurements.

ProtoFit can be used to optimize surface protonation models with up to four discrete surface sites. The models may include the Double Layer Model (DLM), Constant Capacitance Model (CCM), Donnan Shell Model (DSM), and a non-electrostatic model (NEM). Activity coefficients can be modeled by the Davies, Truesdell-Jones, and Extended Debye-Huckel equations, or it can be assumed that activity coefficients equal 1.

For the purpose of protonation model optimization, ProtoFit is an alternative to the widely-used program FITEQL (e.g. Westall, 1982; Herbelin and Westall, 1999)^*. While FITEQL is designed to solve a much wider range of problems, ProtoFit has unique features useful for analysis of titration data as well as a fundamentally different approach to model optimization.

For more information, see the Documentation.

ProtoFit is Free Software licensed under the Gnu General Public License (GPL).

A poster on ProtoFit's methodology and applications was presented at the V.M. Goldschmidt Conference in Moscow, Idaho. It is reproduced in html format on this website.

ProtoFit uses a method of data analysis based on an adsorbent proton buffering function. This quantity expresses the ability of the surface to buffer protons as a function of pH. This is the behavior that potentiometric titrations are designed to measure. Analyzing data via this approach is potentially much more useful than analyzing raw titration data alone.

For a more detailed overview, see the Poster reproduced in html format on this website, and the Documentation for more detailed information.

Figure 1. Adsorbent proton buffering function Q^*_ads is plotted vs. pH. Solid lines indicating model predictions are compared with Q^*_ads calculated from titration data. Error bars indicate uncertainty in measurement. Titration data is for rutile (TiO₂) at an ionic strengths of 0.001, 0.01 and 0.1 M (Hayes et al., 1991 - see poster for reference).

• January 8, 2016: Attention Windows 7/8/10 users: The Windows installer has not been updated in a long time, so the default installation location for ProtoFit 2.1 rev1 and earlier will not work properly with the "newer" versions of Windows. To correct this, first unistall ProtoFit. When re-installing, enter C:\ProtoFit instead of the default C:\Program Files\ProtoFit when the installer asks you to "Select Destination Directory." Otherwise, ProtoFit will not run correctly.
• November 14, 2008: Attention Windows VISTA users: The default install options for ProtoFit 2.1 rev1 and earlier will not work properly with VISTA. To correct this, enter C:\ProtoFit instead of the default C:\Program Files\ProtoFit when the installer asks you to "Select Destination Directory." Otherwise, ProtoFit will not run correctly.
• November 1, 2006: A research article on ProtoFit is available. The article, appearing in the November issue of Computers & Geosciences, discusses the approach used by ProtoFit, factors affecting quality of results, and examples.
• November 23, 2005: ProtoFit 2.1 rev1 is available. This update fixes a bug that caused the contribution of basic functional groups to surface charge to be incorrectly calculated in earlier releases. Details of the changes are described in the release notes.
• September 2, 2005: ProtoFit 2.1 is available. The newest version of ProtoFit provides a number of new features some new usability improvements including: (1) A built-in text editor is added to ProtoFit-GUI. This is particularly advantageous to Windows users who do not have quality text editors installed on their systems, and/or may not be familiar with the use of text editors. (2) The pHzpc calculator routine will not run during optimization mode unless the "Use pHzpc to constrain model" option is selected. In all other cases, a failure of the pHzpc calulator to converge will result in a warning rather than an error. Details of the changes are described in the release notes.
• June 3, 2005: A minor update to ProtoFit, version 2.0 rev1 is available. The changes are with how ProtoFit handles multiple data points with the same pH value. Details of the changes are described in the release notes.
• May 26, 2005: A mailing list is available for people interested in ProtoFit. Subscribe for announcements, etc.
• May 24, 2005: A poster on ProtoFit's methodology and applications was presented at the V.M. Goldschmidt Conference in Moscow, Idaho. It is reproduced in html format on this website.
• April 6, 2005: ProtoFit 2.0 is available. The newest version of ProtoFit provides a number of new features including: (1) Flexibility in choosing any combination of acidic, basic, and amphoteric surface sites. (2) Flexibility in how error weighting is or is not conducted during model optimization. (3) Ability to use pHzpc as a constraint in model optimization. (4) More data analysis plots including total (water + adsorbent) buffer value, and model surface charge. (5) Less dependency on supporting software - ProtoFit-GUI is more portable.
• April 29, 2004: ProtoFit 1.0 rev 1 is available. This release includes an improved speciation solver. The old solver did not always converge, especially for the constant capacitance model (CCM). For additional details regarding the improvements to the speciation solver algorithm, read these notes.
• April 13, 2004: ProtoFit 1.0 is now available. This is the first public release of ProtoFit.

^*References:

Westall, J. C., 1982. FITEQL. A Computer Program for Determination of Chemical Equilibrium Constants, Version 2.1; Report 82-02; Department of Chemistry, Oregon State University: Corvallis, OR.

Herbelin, A.L., Westall, J.C., 1999. FITEQL 4.0: a Computer Program for Determination of Chemical Equilibrium Constants from Experimental Data; Report 99-01. Department of Chemistry, Oregon State University, Corvallis.