Waters 2489, Operator'S Manual

Page: 29 / 234

Operational modes 1-13
inaccuracies because of possible UV light interference (second order
effects).
Chart Out selection modes
When operating in dual wavelength mode, the detector offers these choices for
analog output in addition to the selections offered in single wavelength mode
and explained in
“Single wavelength mode” on page 1-11 . The default
selection for dual wavelength mode is Absorbance.
• Absorbance (A and B) – This is the standard LC mode where the current
absorption is scaled and sent directly out the analog output. The scaling
depends on the AUFS setting and the absorbance offset. The absorbance
value is scaled for the 2-V analog output. If a setting of 1 AU/V is
desired, you can set an AUFS of 2.0000 for either the A or B output
channels that can be controlled independently, even in single
wavelength mode.
• MaxPlot – This mode results in the output of the larger of the two
absorbance values, scaled to the selected AUFS setting. This mode is
useful when looking at multiple compounds with absorbancies at two
separate wavelengths with one data channel.
• RatioPlot (A/B) – This mode produces the ratio of absorbance from two
wavelengths. Theoretically, the ratio is constant for a pure
chromatographic peak and variable for an impure peak. This results in a
nonsquared response. Instead of a programmable AUFS, the detector
provides minimum and maximum ratio values that scale the ratio plot
proportionally. In addition, a configurable minimum absorbance
threshold activates ratio output scaling only when it reaches the
absorbance at both wavelengths.
• Difference Plot (A-B) – This mode plots the arithmetic difference in
absorbance for the two monitored wavelengths.
Spectrum scanning
Note: When the detector is operating under the control of the Empower
software, the scanning function is disabled.
You can use the detector as a spectrophotometer to acquire spectra from either
the flow cell or the cuvette. You can scan and store up to three spectra (three
reference or zero scans, or three sample scans) in memory for playback or to
compare with other spectra.