Waters 2996 - Appendix C; Mobile Phase Absorbance; Mobile Phase Absorbance Measured against Air or Water

Mobile Phase Absorbance 55
C
Appendix C
Mobile Phase Absorbance
This appendix lists 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 in Table C-1.
Table C-1 Mobile Phase Absorbance Measured Against Air or Water
Absorbance at Specified Wavelength (nm)
200 205 210 215 220 230 240 250 260 280
Solvents
Acetonitrile 0.050.030.020.010.01<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