Waters ACQUITY UPLC Operator's, Overview And Maintenance Manual page 25

reference spectrum is a measure of lamp intensity and mobile phase
absorbance. With the shutter open, the reference spectrum is
determined over the interval specified in the exposure time.
Tips:
• For best results, the reference spectrum should represent the initial
mobile phase.
• For extremely long exposure times, the dark current and reference
spectrum readings can take several seconds to finish.
Absorbance
The detector calculates the absorbance for each diode at the end of each
exposure time using the following equation:
Absorbance n
=
where
S = obtained during sample analysis
D = obtained during the dark current test
R = obtained from the reference spectrum
n = diode number
Resolution
The data the detector report to the database (Empower, MassLynx, or
third-party) can be the average of a number of data points. After calculating
absorbance, the detector averages absorbance values based on spectral
resolution and sample rate.
Averaging spectral data based on resolution
Spectral resolution (or bandwidth) is the wavelength interval (in
nanometers) between data points in an acquired spectrum. The
detector's lowest resolution setting is 1.2 nm. For example, in 3D mode,
the detector averages six adjacent diodes for each reported wavelength
when the spectral resolution is set in the software to 3.6 nm. In 2D
mode, absorbance values are computed based on the bandwidth setting.
Averaging chromatographic data based on sample rate
Sample rate is the number of data points acquired per second. The
number of times the photodiodes are read during the sample rate
( )
Sn – Dn
log ------------------------ -
( )
Rn Dn –
Operating principles of the light-guiding flow cell 13