Appendix: Common Mobile Phases - Thermo Scientific Dionex UltiMate 3000 Series Operating Instructions Manual

10 Appendix: Common Mobile Phases

The mobile phase composition affects its UV cutoff, that is, the minimum effective wave-
length for the measurement. In general, mobile phases are solvents, such as, water,
acetonitrile, methanol, or other substances. They may also contain salts, such as NaOH.
If the excitation monochromator of a fluorescence detector is set below the UV cutoff of the
mobile phase, the solvent will absorb some of the excitation light. Thus, the excitation
wavelength should always be above the UV cutoff of the solvent (recommendation: min.
30 nm).
The UV cutoff wavelengths of these solvents may differ from those predicted by Table 1.
Among other factors, the degassing quality and purity grade of the solvent affect the UV
cutoff. Therefore, the values listed below are approximate values only. The cutoffs listed in
the table apply to HPLC-grade solvents.
Solvent
Acetic acid
Acetone
Acetonitrile
Dioxane
Ethanol
Ethyl acetate
Hexane sulfonic acid (0.005 M)
Methanol
Methylene chloride
n-Hexane
Octane sulfonic acid
Sodium carbonate (0.01 M)
Sodium hydroxide (0.1 M)
Tetrabutylammonium hydroxide (0.005 M)
Tetrahydrofuran
Tetrapropylammonium hydroxide
Toluene
Triethylamine
Water
Operating Instructions
Fluorescence Detectors FLD-3100 and FLD-3400RS
UV Cutoff
(nm)
208
330
190
215
210
256
230
205
233
190
230
210
217
215
212
195
285
Table 1: Properties of frequently used mobile phases
UltiMate 3000 Series:
Refractive Selectivity
Index Group
IV
1.37
VIa
1.356
VIb
1.341
VIa
1.42
II
1.359
VIa
1.37
II
1.326
V
1.421
VII
1.372
III
1.405
VII
1.494
I
1.398
VIII
1.333
Page 123