The integrator has three peak recognition filters that it can use to recognize peaks by detecting changes in the slope and curvature within a set of contiguous data points. These filters contain the first derivative (to measure slope) and the second derivative (to measure curvature) of the data points being examined by the integrator.
In order to deliver reliable results the peak must contain at least ten data points. |
The recognition filters are:
Slope (curvature) of two (three) contiguous data points
Slope of four contiguous data points and curvature of three non-contiguous data points
Slope of eight contiguous data points and curvature of three non-contiguous data points
The actual filter used is determined by the peak width setting. For example, at the start of an analysis, Filter 1 may be used. If the peak width increases during the analysis, the filter is changed first to Filter 2 and then to Filter 3. To obtain good performance from the recognition filters, the peak width must be set close to the width of the actual chromatographic peaks. During the run, the integrator updates the peak width as necessary to optimize the integration.
The integrator calculates the updated peak width in different ways, depending on the instrument technique.
For LC data, the default peak width calculation uses a composite calculation:
0.3 * (Right Inflection Point - Left Inflection Point) + 0.7 * Area / Height
For GC data, the default peak width calculation uses area/height. This calculation does not overestimate the width when peaks are merged above the half-height point.
In certain types of analysis, for example isothermal GC and isocratic LC analyses, peaks become significantly broader as the analysis progresses. To compensate for this, the integrator automatically updates the peak width as the peaks broaden during the analysis. It does this automatically unless the updating has been disabled with the fixed peak width timed event.
The peak width update is weighted in the following way:
0.75 * (Existing Peak Width) + 0.25 * (Width of Current Peak)