How to Characterize a Column

Column characterization is the first step in building a mechanistic model. The goal is to determine column parameters: porosity, axial dispersion, and ionic capacity from simple non-binding tracer and titration experiments.

Overview

Before you can calibrate binding parameters, the column transport model needs to be in place. If the transport parameters are wrong, every downstream fit will compensate for that error, and the model will not extrapolate well.

Column characterization uses pulse injection experiments with non-binding tracers. Because no adsorption is involved, the chromatogram depends only on the column geometry, packing quality, and flow characteristics. This makes it possible to determine column parameters independently of binding.

A typical characterization involves:

1. Measuring column dimensions (height, inner diameter). This is typically provided by the manufacturer if you are using pre-packed columns.
2. Performing a pulse injection with column detached from the system, to measure the system volume (volume between injection valve and detector).
3. Performing a pulse injection with a small tracer (e.g. acetone or NaCl).
4. Performing a pulse injection with a large tracer (e.g. Blue Dextran).
5. If you need the ionic capacity, run a on-column titration experiment.

This is usually the quickest part of the modeling workflow — a few hours of lab time and a short fitting session. Once done, the column parameters can be reused for all subsequent binding calibrations on the same column.

Setting Up the System Model

Running Pulse Injection Experiments

Importing Experimental Data

Fitting Transport Parameters

Validating the Characterization