Solvent miscibility C-3
Buffers
When you use buffers, dissolve salts first, adjust the pH, then filter to remove
insoluble material.
Tetrahydrofuran (THF)
When using unstabilized THF, ensure that your solvent is fresh. Previously
opened bottles of THF contain peroxide contaminants, which cause baseline
drift.
Solvent miscibility
Before you change solvents, consult the following table to determine the
miscibility of the solvents to be used. When you change solvents, be aware
that:
• Changes involving two miscible solvents may be made directly. Changes
involving two solvents that are not totally miscible (for example, from
chloroform to water), require an intermediate solvent (such as
isopropanol).
• Temperature affects solvent miscibility. If you are running a
high-temperature application, consider the effect of the higher
temperature on solvent solubility.
• Buffers dissolved in water may precipitate when mixed with organic
solvents.
When you switch from a strong buffer to an organic solvent, flush the buffer
out of the system with distilled water before you add the organic solvent.
Warning: THF contaminants (peroxides) are potentially explosive
when concentrated or taken to dryness.
Solvent miscibility
Polarity
index
Solvent
Viscosity
CP, 20 °C
Boiling
point °C
(1 atm)
Miscibility
number
(M)
λ Cutoff
(nm)
–0.3 N-decane 0.92 174.1 29 ––
–0.4 Iso-octane 0.50 99.2 29 210
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