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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.
The absorbances in the table below are based on a 10-mm pathlength.
Tip:
Mobile phase absorbance measured against air or water
Absorbance at specified wavelength (nm)
200
Solvents
Acetonitrile
0.05
Methanol
2.06
(not
degassed)
Methanol
1.91
(degassed)
Isopropanol
1.80
Unstablized
2.44
tetrahydro-
furan
(THF), fresh
Unstablized
>2.5
tetrahydro-
furan
(THF), old
205
210
215
0.03
0.02
0.01
1.00
0.53
0.37
0.76
0.35
0.21
0.68
0.34
0.24
2.57
2.31
1.80
>2.5
>2.5
>2.5
220
230
240
0.01
<0.01 —
0.24
0.11
0.05
0.15
0.06
0.02
0.19
0.08
0.04
1.54
0.94
0.42
>2.5
>2.5
>2.5
Wavelength selection
250
260
280
—
—
—
0.02
<0.01 —
<0.01 —
—
0.03
0.02
0.02
0.21
0.09
0.05
>2.5
2.5
1.45
C-15
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