In addition, the viscosity of a binary mixture of unassociating solvents, canbe calculated using an equation developed by Moore et al. [20], viz,
(52)
| where (y1) | is the mole fraction of solvent (1), |
| (y2) | is the mole fraction of solvent (2), |
| (h1) | is the viscosity of solvent (1), |
| and (h1) | is the viscosity of solvent 2. |
By employing
the viscosity values calculated for a range of temperatures and solvent
mixtures in equation (50) the effect of temperature and solvent composition on
the optimum mobile phase velocity could be calculated. A practical initial
value for (
) was assumed to be 2.5 x 10-5 cm2s.
This value was taken as the probable estimate from publishd data for similar
compounds (21,22) for the diffusivity of the (R)-enantiomer at 20˚C in a
solvent mixture containing 10%v/v of ethanol and consequently may not be a
highly accurate value. Nevertheless, it will allow the relative effect of
temperature and solvent composition on the optimum mobile phase velocity and
analysis time to be demonstrated. The optimum mobile phase velocities were
calculated using the above equations and experimental data, and the results
obtained are shown as graphs relating optimum velocity to temperature for a
range of different solvent mixtures in figure 25.
