Axis BTA 2100D Manual do Operador descarregar pdf (Página 438)

436

Peak Detection

The Varian MS Workstation software reduces the raw data collected from the

chromatograph into a results report in four steps:

 Peak detection

 Peak integration (and final baseline determination)

 Peak identification (if a Peak Table is present)

 Results calculations

Peak detection is the process in which the peak start, apex, and end points are

determined. This is also the step where fused peaks are identified as a

mother/tangent peak pair, or as two valley separated main peaks.

The programmable time events that affect the peak detection process are Peak

Width, Signal to Noise Ratio, Inhibit Integrate, Tangent Percentage, and Forced

Peak. These are discussed in more detail later in this section.

Once the peaks are detected, the area for the peaks is determined in the peak

integration step. The first part of this step is to process any Split Peak events.

This event causes a previously detected peak to be treated as two separate

peaks. Tied to both peak detection and peak integration is baseline placement.

The four time events which affect baseline placement do not affect peak

detection. These events are Valley Baseline, Horizontal Forward, Horizontal

Backward, and Horizontal Minimum.

After areas for all peaks have been calculated, the optional step of peak

identification is done. Before peaks are identified, they may be excluded from

consideration by the Solvent Reject event or the Peak Reject event. Also, several

peaks may be treated as one peak by the Group Peak event. Peak identification

is the process by which peaks detected in the first step, and integrated in the

second, are matched by retention time with a list of peaks you have previously

entered in the Peak Table. As described below in more detail, Interactive

Graphics provides a fast and efficient means of building the Peak Table using

your pilot run.

The final step is to perform one or more of a large variety of possible calculations

producing the final results. This produces results in a state suitable for printing or

exporting by the Report application.

Peak Width Determination

In general, peaks are wider in liquid chromatography than they are in gas

chromatography. To account for potential wide differences in peak width from run

to run, you can set an initial peak width parameter. The lower the peak width

value, the more accurate the placement of peak events. However, if set too low,

a wide low peak may not be detected.

Peaks tend to widen with the retention time. The Data Handling software can

account for this by automatically programming peak width events at appropriate

times. This way, early eluting narrow peaks can use a low and more accurate

peak width setting, while later eluting wide peaks will be properly detected with a

higher peak width setting. To do automatic peak width programming, the peak

detection software monitors peak widths as peaks are detected. If it determines

that peaks are getting too wide relative to the current peak width setting, it

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