June 11, 2015, 715004752 Rev. A
Page 25
1.3.3 Spectrum scanning
When the detector is operating under the control of the chromatography data
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, when required. You can scan and store as many as three
spectra (three reference or zero scans, or three sample scans) for playback or to
compare with other spectra.
The major difference between the detector and a double-beam spectrophotometer is
that the detector uses only one flow cell, or cuvette when required, rather than a
sample and a reference pair.
Recommendation:
If your flow cell requires a cuvette, use a matched pair of
cuvettes for the zero and sample scans.
The detector obtains an absorbance spectrum by performing two types of scans on
the flow cell or using the cuvette:
•
Zero scan – Characterizes the baseline absorbance spectrum of a solvent.
•
Sample scan – Subtracts the zero scan, so the results displayed or charted are
of the sample only.
To obtain a spectrum of a sample using the detector, run a zero scan first, followed by
a sample scan. Typically, you run the zero scan using pure solvent. The sample scan is
a scan of the analyte dissolved in that solvent.
Spectra can be simultaneously charted on the channel A output, or acquired and
stored in memory for later playback.
See also:
“Scanning using the cuvette” on page 88
.
RatioPlot (A/B)
Produces the ratio of absorbance from
two wavelengths. Theoretically, the ratio
is constant for a pure chromatographic
peak and variable for an impure peak,
which results in a nonsquared response.
Instead of a programmable AU, 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)
Plots the arithmetic difference in
absorbance for the two monitored
wavelengths.
Table 1–6:
Additional options for analog output in dual-wavelength mode
Mode option
Description of mode
Summary of Contents for 2489
Page 2: ...June 11 2015 715004752 Rev A Page ii...
Page 8: ...June 11 2015 715004752 Rev A Page viii...
Page 14: ...June 11 2015 715004752 Rev A Page xiv...
Page 46: ...June 11 2015 715004752 Rev A Page 46...
Page 124: ...June 11 2015 715004752 Rev A Page 124...
