Solvent Viscosity - Waters ACQUITY UPLC M-Class System Manual

• 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.
D.6 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.
November 26, 2019, 715003588 Revision C
Page 117