How To Use Miscibility Numbers (M-Numbers) - Waters Alliance e2695 Operator's Manual

Table D–6: Solvent miscibility
Polarity
index
4.8
5.2
5.3
5.3
5.4
5.5
5.7
6.2
6.2
6.4
6.5
6.6
7.3
9.0
D.3.1

How to use miscibility numbers (M-numbers)

Use miscibility numbers (M-numbers) to predict the miscibility of a liquid with a standard solvent.
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.
• A difference of 16 indicates a critical solution temperature between 25 and 75 °C, with 50 °C
as the optimal temperature.
• If 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 cut-off point for
miscibility.
Viscosity
Solvent
CP, 20 °C
Dioxane 1.54
Ethanol 1.20
Pyridine 0.94
Nitroethane 0.68
Acetone 0.32
Benzyl alcohol 5.80
Methoxyethanol 1.72
Acetonitrile 0.37
Acetic acid 1.26
Dimethylformamide 0.90
Dimethylsulfoxide 2.24
Methanol 0.60
Formamide 3.76
Water 1.00
February 27, 2018, 715003794 Rev. C
Boiling
point °C
(@1 atm)
101.3
78.3
115.3
114.0
56.3
205.5
124.6
81.6
117.9
153.0
189.0
64.7
210.5
100.0
Page 229
 cut-off
Miscibility
number (M) (nm)
17 220
14 210
16 305
–– ––
15, 17 330
13 ––
13 ––
11, 17 190
14 ––
12 ––
9 ––
12 210
3 ––
–– ––