Donnan UF/DF Calculator — QATCH Technologies

This tool is an open Donnan/UF/DF screening model based on a simplified version of:

Kannan et al., Predicting Formulation Conditions During Ultrafiltration and Dilution to Drug Substance Using a Donnan Model with Homology-Model Based Protein Charge, J. Pharmaceutical Sciences, 112 (2023). doi:10.1016/j.xphs.2022.10.028

This is not the original Kannan model and should be considered an approximate educational / screening implementation.

What the model estimates

Buffer concentration shifts across the UF/DF membrane
Ionic redistribution of charged species
Approximate pH changes during UF/DF

Supported components

Histidine — weak buffer (Henderson–Hasselbalch)
Acetate — weak buffer (Henderson–Hasselbalch)
Arginine
NaCl

Counterions may be automatically added internally to maintain electroneutrality.

Protein charge input

Direct Z and dZ/dpH (preferred) — can be estimated from sequence data using the tools below.
Estimated from pI and protein type — mAb, Fab, generic, and polyclonal options are simplified heuristics not in the original paper.

Free charge estimation tools

Simplifications vs. original paper

Protein charge
Buffer thermodynamics
Donnan equilibrium
Ionic strength / activity corrections
Molecular structure effects

This software is provided "as is" without warranty of accuracy, fitness for a particular purpose, or regulatory suitability.

Users are responsible for validating results experimentally before use in research, development, manufacturing, or process decisions.

This tool is intended for educational and early-stage screening purposes only and does not constitute regulatory or engineering advice.

Questions, feedback, or want to learn more about QATCH's viscosity and injectability solutions? We'd love to hear from you.

Or email us directly: info@qatchtech.com

Formulation Inputs

DF / Permeate Buffer

Buffer pH pH units

Histidine mM total

Acetate mM total

NaCl mM

Arginine mM total

Protein

Concentration mg/mL

MW kDa

Protein Charge

Charge Z at buffer pH e

dZ/dpH e/pH

Predicted Retentate

Ready to calculate

Configure your formulation parameters and click Calculate Retentate to predict Donnan-shifted conditions.

Model: Kannan et al. (2023) J. Pharm. Sci. Coupled pH solve with molal Donnan equilibrium and volume exclusion. Ideal buffer speciation; no Debye–Hückel correction. doi:10.1016/j.xphs.2022.10.028