Technical data

Understanding Your Agilent ChemStation 75

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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