Waters 2998, Обзор и руководство по обслуживанию

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December 5, 2017, 715004753 Rev. B
Page 23
1.5.1 Dark current
Photodiodes discharge even when they are not exposed to light. This discharge is called dark
current. The dark current is updated by closing the shutter to take a dark current reading for each
diode. After updating, the detector opens the shutter and then subtracts the dark current values as
shown in the above equation.
1.5.2 Reference spectrum
The reference spectrum is a measure of lamp intensity and mobile phase absorbance at initial
conditions. The detector records a reference spectrum at the start of each injection. The value of
that spectrum is calculated using the same filter-time constant as the absorbance data.
1.5.3 Data averaging
The data the detector reports to the database (Empower or MassLynx) can be the average of data
points. After calculating absorbance, the detector averages absorbance values on the basis of the
requested spectral resolution.
1.5.3.1 Average spectral resolution
The detector can simultaneously collect two types of data channels: spectra (3D) and
chromatograms (2D). For best results in library matching and peak-purity analysis, set the 3D
resolution to 1.2 nm.
For chromatograms (2D data), select a resolution to optimize signal amplitude, baseline noise, and
linear dynamic range. When the monitoring wavelength for an analyte corresponds to a peak’s
lambda max, increasing bandwidth tends to decrease peak height while reducing baseline noise
and linear dynamic range.
Tip:
A resolution of 4.8 nm is effective for many analytes.