Waters 2998, Operator'S Manual

Page: 21 / 122

Computing absorbance data points 1-9
Computing absorbance data points
The absorbance data points are calculated by the detector and then
transmitted to the database (MassLynx or Empower).
The absorbance calculation is
where
S = sample energy
D = dark energy
R = reference energy
t = elapsed time after start of injection
λ = wavelength
This value is then filtered as specified.
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.
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 reference spectrum value is calculated using
the same filter time constant as the absorbance data.
Data averaging
The data the detector reports to the database (
Empower or MassLynx
) can be the
average of a number of data points. After calculating absorbance, the detector
averages absorbance values based on the requested spectral resolution.
Absorbance
t λ ,
Log
10
R
λ
D
λ
–
S
t λ ,
D
λ
–
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=