Waters 2998, Overview And Maintenance Manual

Page: 92 / 94

December 5, 2017, 715004753 Rev. B
Page 92
*Willard, H. H. and others.
Instrumental Methods of Analysis
, 6th ed. Litton Educational Publishing, Inc., 1981. Reprinted by
permission of Wadsworth Publishing Co., Belmont, California, 94002.
C.9.4 Mobile phase absorbance
This section lists the absorbances at several wavelengths for frequently used mobile phases.
Choose the mobile phase carefully to reduce baseline noise.
The best mobile phase for your application is one that is transparent at the chosen detection
wavelengths. With such a mobile phase, ensure 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 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.
Allene —(C=C)4— 300 52,000
Allene —(C=C)5— 330 118,000
Allene —(C=C)2—
(alicyclic) 230-260 3000-8000
Ethylenic/
Acetylenic C=C—C

C 219 6,500
Ethylenic/
Amido C=C—C=N 220 23,000
Ethylenic/
Carbonyl C=C—C=O 210-250 10,000-
20,000
Ethylenic/
Nitro C=C—NO2 229 9,500
Table C–5: 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
Table C–4: Electronic absorption bands of representative chromophores (continued)*
Chromophore
Chemical
Configuration

max
(nm)

max
(L/m/cm)

max
(nm)

max
(L/m/cm)