Operational modes 1-15
that blocks unwanted ultraviolet (UV) light from reaching the diffraction
grating, which can interfere with fluorescence detection of 400 nm and longer.
Selecting the appropriate sampling rate
A sufficient number of points must fall across a peak to define its shape. For
this reason, the definition between peaks is lost at very low sampling rates.
Empower uses the index of the data point closest to the end time, minus the
index of the data point closest to the start time, to calculate the Points Across
Peak value for each integrated peak in the chromatogram.
Tip: The Points Across Peak value appears in the Peaks table, at the bottom of
the Review Main window. If the Points Across Peak field is not visible,
right-click anywhere in the table, and then click Table Properties. Click the
Columns tab, and then scroll down to find the Points Across Peak field. Clear
the check box, and then click OK.
If the Points Across Peak value for the narrowest peak of interest is less than
25, you must specify a higher sampling rate in the instrument method. If the
value is greater than 50, you should specify a lower sampling rate in the
instrument method.
Set the sampling rate to the lowest value required to achieve 25 or more
points across the narrowest peak. Excessively high sampling rates exhibit
higher noise levels.
Multichannel mode
In multichannel, or multiwavelength mode, the detector monitors two or more
excitation/emission wavelength pairs. The sampling frequency range is
reduced, limiting the use of this mode to a more standard chromatography,
where peaks are not excessively narrow. You can use multiwavelength mode
to obtain additional information about an analyte by running a Difference Plot
or a MaxPlot. The detector allows you to select up to four excitation
wavelengths from 200 to 890 nm and up to four emission wavelengths from
210 to 900 nm. For the best signal-to-noise ratio, set a gain that maximizes
the dynamic range of the electronics. A gain that is too high overloads the
pre-amplifier, resulting in flat-topped peaks and a warning alarm.
MaxPlot
The detector allows you to obtain a MaxPlot in multichannel mode. The
MaxPlot function monitors fluorescence at the selected excitation/emission
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