Kinetic titration

The kinetic titration (single cycle kinetics) is useful with interactions which are difficult to regenerate or when regeneration is detrimental to the ligand (1). In addition, it can be used to determine the concentration and kinetic range of an interaction. During the kinetic titration, the analyte is injected from a low to high concentration with short dissociation times in between and a long dissociation time at the end. The short and long dissociation times will speed up the injection sequence. All the analyte injections are analysed in the same sensorgram with a special equation for kinetic titration. The model is based on the one to one binding interaction and is limited to five analyte injections (2). A mass transfer component (k_t) and drift are added in de model.

Reaction equation

Differential equation

Response calculation

Because it is not possible to solve this type of injection with a differential model, a numeric model is used. In the numerical model each analyte injection is individually fit, and the total response calculated. The numerical model also contains terms for mass transport, drift and bulk refractive index mismatches.

Numeric model

Although in the parameter table the RI and Drift are locally fit, they are in the model set to a constant of zero. It is better to start to fit the curves without these parameters. When the kinetic parameters are known, then it is possible to add refractive index bulk effect or drift.

Below an example of a sensorgram generated with the differential equations from above.