PDA-100 Photodiode Array Detector
3-26
Doc. 031644-02 9/03
Negative Absorbance
NOTE The NegativeAbsorptionLevel command is available
only if you are running PeakNet 6.40 SP3 (or later) or
Chromeleon 6.50 SP1 (or later)
and
PDA-100
Moduleware version 2.0 (or later).
Negative absorbance is the result of decreased absorption of the eluent after
autozero (which usually occurs at the beginning of a run). Depending on certain
buffer conditions, this shift can result in flat baselines or truncated peaks; if this
occurs, increase the
NegativeAbsorptionLevel
setting to shift the detection level.
This is especially helpful when running a gradient application in which the
absorbance decreases more than several hundred mAU.
For example, in Figure 3-7, the
NegativeAbsorptionLevel
setting is -100 initially
and the baseline is flat when the gradient is
≤
50%. The baseline is not flat when
the gradient is >5% and the
NegativeAbsorptionLevel
is set to -600.
Figure 3-7. Gradient Baseline with NegativeAbsorptionLevel Settings of -100 and -600
Pump Gradient
75%
50%
25%
NegativeAbsorptionLevel = -100
NegativeAbsorptionLevel = -600
