Waters 2998, Обзор и руководство по обслуживанию

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December 5, 2017, 715004753 Rev. B
Page 84
C.1.5 Use buffers
When you use buffers, dissolve salts first, adjust the pH, then filter to remove insoluble material.
C.1.6 Tetrahydrofuran
When using unstabilized tetrahydrofuran, ensure that your solvent is fresh. Previously opened
bottles of tetrahydrofuran contain peroxide contaminants, which cause baseline drift.
C.2 Solvent miscibility
Before you change solvents, refer to the table below to determine the miscibility of the solvents to
be used. When you change solvents, be aware of these miscibility principles:
• Changes involving two miscible solvents may be made directly, but changes involving two
solvents that are not totally miscible (for example, from chloroform to water) require an
intermediate solvent, like 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 can precipitate when mixed with organic solvents.
When you switch from a strong buffer to an organic solvent, flush the buffer from the system using
distilled water before you add the organic solvent.
Warning:
Tetrahydrofuran contaminants (peroxides) are potentially explosive if
concentrated or taken to dryness.
Table C–1: Solvent miscibility
Polarity
Index
Solvent
Viscosity
CP, 20

C
Boiling
Point

C
(1 atm)
Miscibility
Number (M)

Cutoff
(nm)
–0.3 N-decane 0.92 174.1 29 ––
–0.4 Iso-octane 0.50 99.2 29 210
0.0 N-hexane 0.313 68.7 29 ––
0.0 Cyclohexane 0.98 80.7 28 210
1.7 Butyl ether 0.70 142.2 26 ––
1.8 Triethylamine 0.38 89.5 26 ––
2.2 Isopropyl ether 0.33 68.3 –– 220
2.3 Toluene 0.59 100.6 23 285
2.4 P-xylene 0.70 138.0 24 290
3.0 Benzene 0.65 80.1 21 280
3.3 Benzyl ether 5.33 288.3 –– ––
3.4 Methylene chloride 0.44 39.8 20 245
3.7 Ethylene chloride 0.79 83.5 20 ––