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
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
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
Summary of Contents for 2998
Page 12: ...xii Table of Contents...
Page 26: ...1 14 2998 PDA Detector Optics Principles...
Page 62: ...3 12 Maintaining the Detector...
Page 82: ...5 10 Spectral Contrast Theory...
Page 96: ...A 14 Safety Advisories...
