Using Miscibility Numbers (M-Numbers) - Waters ACQUITY UPLC M-Class System Manual

Table D–2: Solvent miscibility
Polarity
index
0.0
1.8
4.3
4.3
5.2
5.5
5.7
6.2
6.2
6.4
6.5
6.6
9.0
D.5.1 Using 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.
• When 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 from 25 to 75 °C, with 50 °C as the
optimal temperature.
• 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:
Solvent Viscosity cP,
20 °C
(@1atm)
N-hexane 0.313
Triethylamine 0.38
1-propanol 2.30
2-propanol 2.35
Ethanol 1.20
Benzyl 5.80
alcohol
Methoxyethan 1.72
ol
Acetonitrile 0.37
Acetic acid 1.26
Dimethylform 0.90
amide
Dimethylsulfo 2.24
xide
Methanol 0.60
Water 1.00
November 26, 2019, 715003588 Revision C
Page 116
Boiling Miscibility
point °C number (M)
(@1atm)
68.7 29
89.5 26
97.2 15
117.7 15
78.3 14
205.5 13
124.6 13
81.6 11, 17
117.9 14
153.0 12
189.0 9
64.7 12
100.0 —
λ cutoff (nm)
—
—
210
—
210
—
—
190
—
—
—
210
—