Wavelength selection C-15
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
the autozero function cancels, or “autozeroes,” out. Wavelength, pH, and
concentration of the mobile phase affects its absorbance. Examples of several
mobile phases are given in the table below.
Tip: The absorbances in the table below are based on a 10-mm pathlength.
Mobile phase absorbance measured against air or water
Absorbance at specified wavelength (nm)
200 205 210 215 220 230 240 250 260 280
Solvents
Acetonitrile0.050.030.020.010.01<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 — —
Isopropanol1.800.680.340.240.190.080.040.030.020.02
Unstablized
tetrahydro-
furan
(THF), fresh
2.44 2.57 2.31 1.80 1.54 0.94 0.42 0.21 0.09 0.05
Unstablized
tetrahydro-
furan
(THF), old
>2.5 >2.5 >2.5 >2.5 >2.5 >2.5 >2.5 >2.5 2.5 1.45
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