The symmetry of and in this version erases the distinction between upper and lower, and the two functions are then called polarities rather than adjoints.
Here, the polarity of the stationary phase can be varied by temperature changes, altering the power of separation without changing the column or solvent composition.
In fact, charge-transfer transitions of ground state ion-pairs give the largest changes in absorption spectra, and are thus, the most useful for measuring solvent polarity.
