Allocating The Baseline - Agilent Technologies 8453 Operator's Manual

4
Integration
Overview

Allocating the Baseline

The integrator allocates the chromatographic/electropherographic baseline
during the analysis at a frequency determined by the peak width value. When
the integrator has sampled a certain number of data points, it resets the
baseline from the initial baseline point to the current baseline point. The
integrator resumes tracking the baseline over the next set of data points and
resets the baseline again. This process continues until the integrator identifies
the start of a peak
Figure 4 Baseline
At the start of the run, this baseline setting is used as the beginning baseline.
If this is not set, the first data point is used. This baseline point is then
periodically reset according to the following formula:
Areas are summed over a time T (expected peak width). This time can never be
shorter than one data point. This continues as long as baseline condition
exists. Slope and curvature are also taken. If both slope and curvature are less
than the threshold, two summed areas are added together, and compared with
the previous baseline. If the new value is less than the previous baseline, the
new value immediately replaces the old one. If the new value is greater than
the previous value, it is stored as a tentative new baseline value and is
confirmed if one more value satisfies slope and curvature flatness criteria.
This latter limitation is not in effect if negative peaks are allowed. During
baseline, a check must also be made to examine fast rising solvents. They may
be too fast for upslope detection. (By the time upslope is confirmed, solvent
criterion may no longer be valid.) At first time through the first data point is
baseline. It is replaced by the 2 T average if signal is on base. Baseline is then
reset every T (see Figure 4 on page 75).
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