Wavelength Selection - Waters ACQUITY UPLC Operator's, Overview And Maintenance Manual

How to use miscibility numbers
Use miscibility numbers (M-numbers) to predict the miscibility of a liquid
with a standard solvent (see
To predict the miscibility of two liquids, subtract the smaller M-number value
from the larger M-number value.
• If the difference between the two M-numbers is 15 or less, the two
liquids are miscible in all proportions at 15 °C (59 °F).
• A difference of 16 indicates a critical solution temperature from 25 to
75 °C (77 to 167 °F), with 50 °C (122 °F) as the optimal temperature.
• If the difference is 17 or greater, the liquids are immiscible or their
critical solution temperature is above 75 °C (167 °F).
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, 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.

Wavelength selection

This section includes UV cutoff ranges for
• common solvents.
• common mixed mobile phases.
• chromophores.
102
"Solvent miscibility" on page 100.)