Solvent Viscosity - Waters ACQUITY UPLC I-Class IVD System Manual

D Solvent Considerations
• When the difference is 17 or greater, the liquids are immiscible, or their
critical solution temperature is above 75 °C.
Some solvents prove immiscible with solvents at both ends of the lipophilicity
scale. These solvents receive a dual M-number:
• The first number, always lower than 16, indicates the degree of
miscibility with highly lipophilic solvents.
• The second number applies to the opposite end of the scale. A large
difference between these two numbers indicates a limited range of
miscibility.
For example, some fluorocarbons are immiscible with all the standard
solvents and have M-numbers of 0 and 32. Two liquids with dual M-numbers
are usually miscible with each other.
A liquid is classified in the M-number system by testing for miscibility with a
sequence of standard solvents. A correction term of 15 units is then either
added or subtracted from the cutoff point for miscibility.

Solvent viscosity

Generally, viscosity is not a consideration when you operate with a single
solvent or under low pressure. However, with gradient chromatography, the
viscosity changes that occur as the solvents are mixed in different proportions
can effect pressure changes during the run. For example, a 1:1
water/methanol mixture produces twice the pressure of either water or
methanol alone.
If you do not know the extent to which pressure changes affect the analysis,
monitor the pressure during the run.
90 July 7, 2014, 715003736IVD Rev. C