D-6 Solvent Considerations
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.
Buffered solvents
When using a buffer, obtain a good quality reagent and filter it through a
0.45-
µm syringe filter.
Do not leave the buffer in the pump upon shutdown. Once the run is complete,
remove the column and clean the buffer out completely by flushing the outlet
line, inlet line, and filter with approximately 40 mL of Milli-Q water
containing 0.2% sodium azide. Use a syringe to flush distilled water through
the vent holes while running the pump.
After flushing with water, flush the pump with 10% methanol before
shutdown. Store the pump in 10% methanol/water during the shutdown.
Solvent head height
The Waters Prep system is flexible in allowing you where to position the
solvent reservoirs. Ideally, the reservoirs should be positioned approximately
level with the pump heads, particularly at flow rates of 2.0 mL/min or less.
However, well maintained (good plunger seals) pump heads are able to
self-prime and draw well sparged solvent from a level beneath the pump
heads. When drawing solvent from containers on the floor beneath the bench,
well sparged solvent is critical. Gas in the solvent can come out of solution as
the pump draws and reduces pressure in the solvent tubing.
Solvent viscosity
It is important to keep in mind that when running a gradient, the viscosity
changes which occur as the solvents are mixed in different proportions can
result in Pressure changes during the run. For example, a 1:1 mixture of
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