Waters 1500-Series, Operator'S Manual

Page: 176 / 188

C-8 Solvent Considerations
How to use miscibility numbers (M-numbers)
Use miscibility numbers (M-numbers) to predict the miscibility of a liquid
with a standard solvent (see the table above).
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 cutoff point for miscibility.
Buffered solvents
When using a buffer, use a good quality reagent and filter it through a
0.45-µm filter.
Do not leave the buffer stored in the system after use. Flush all fluidic
pathways with HPLC-quality water before shutting down the system and
leave water in the system (flush with 90 percent HPLC-quality water:10
percent methanol for shutdowns scheduled to be more than one day). Flush
using a minimum of 15 mL.