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Appendix D
Mobile Phase Absorbance
This appendix provides a list of the absorbances at several wavelengths for commonly
used mobile phases. Choose your mobile phase carefully to reduce baseline noise.
The best mobile phase for your application is one that is transparent at the chosen
detection wavelengths. Such a mobile phase ensures that any absorbance is due only to
the sample. Absorbance by the mobile phase also reduces the linear dynamic range of the
detector by the amount of absorbance that is autozeroed out. Wavelength, pH and
concentration of the mobile phase will affect its absorbance. Examples of several mobile
phases are provided below.
Table D-1 Mobile Phase Absorbance Measured Against Air or Water
Absorbance at Specified Wavelength (nm)
200
205
210
215
220
230
240
250
260
280
Acetonitrile
0.05
0.03
0.02
0.01
0.01
<0.01
—
—
—
—
Methanol (not
degassed)
2.06
1.00
0.53
0.37
0.24
0.11
0.05
0.02
<0.01
—
Methanol
(degassed)
1.91
0.76
0.35
0.21
0.15
0.06
0.02
<0.01
—
—
Isopropanol
1.80
0.68
0.34
0.24
0.19
0.08
0.04
0.03
0.02
0.02
Unstablized
Tetrahydrofuran
(THF, fresh)
2.44
2.57
2.31
1.80
1.54
0.94
0.42
0.21
0.09
0.05
Unstablized
Tetrahydrofuran
(THF, old)
>2.5
>2.5
>2.5
>2.5
>2.5
>2.5
>2.5
>2.5
2.5
1.45
Solvents
D
70
Appendix D