ProteOn XPR36, User Manual

Page: 102 / 288

ProteOn XPR36 | Experiments
84
Experiments with Highly Refractive
Cosolvents (DMSO)
In experiments where analytes are dissolved in highly refractive index
cosolvents such as DMSO, the ligand surface produces a smaller bulk solvent
response than the reference surface. This is known as the excluded volume
(EV) effect. This reduced bulk signal results from the cosolvent being excluded
from the interaction spot surface by the large ligand molecules.
To correct the data for excluded volume effects, a calibration curve must be
generated by injecting three to six different concentrations of cosolvent (in
running buffer) that are less than, equal to, and greater than the samples’
cosolvent concentration.
An EV correction wizard analyzes the calibration data and applies the EV
correction to the reference data.
To run the EV correction wizard:
• On the menu bar click Process > Channel Reference > Correct for
Excluded Volume
The illustrations that follow show the interaction data from 4-carboxybenzene-
sulfonamide (CBS) in 1% DMSO interacting with carbonic anhydrase II (CA II)
both before and after the excluded volume correction was applied.
Figure 1. CA II/CBS interaction data without excluded volume correction.