Waters 2998, Обзор и руководство по обслуживанию

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December 5, 2017, 715004753 Rev. B
Page 19
Figure 1–5: Photodiodes discharged by light
The detector measures the amount of charge required to recharge each photodiode. The charge is
proportional to the amount of light transmitted through the flow cell over the interval specified by
the diode exposure time.
1.4.1 Optimizing the signal-to-noise ratio
To optimize signal-to-noise ratios, choose an acquisition wavelength range that includes only the
wavelengths of interest. It is also important that the range be one in which the mobile phase
absorbs only minimally. You can also improve the signal-to-noise ratio by increasing the spectral
resolution value. For example, you can choose to operate at 3.6 nm instead of at 1.2 nm
resolution. The signal-to-noise ratio is also affected by the filter-time constant and the sampling
rate.
1.4.2 Selecting the appropriate sampling rate
A sufficient number of points must fall across a peak, to define its shape. Thus the definition
between peaks is lost at very low sampling rates. Empower
®
uses the end time minus 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 Points Across Peak check box, and then click OK.
If the points-across-peak value for the narrowest peak of interest is less than 25, specify a higher
sampling rate in the instrument method. If the value is greater than 50, specify a lower sampling
rate in the instrument method.
Mirror
Grating
Flow cell
Deuterium lamp
Light from grating
dispersed onto diodes.
Sample in flow cell
absorbs at specific
wavelengths.
Slit