Area Peak Factor Calculations
The Model Background dialog will also calculate the background corrected peak and integrated areas using a cubic spline fit to the intensity data. These are useful for Area Peak Factor (APF) calculations. The program will calculate both the P/I (Peak/Integrated, normally the “standard” or reference compound) and the I/P (Integrated/Peak, normally the “unknown” compound) values. The one that is ultimately utilized for an APF calculation by the user depends on whether the wavescan represents the primary standard or the secondary standard. See the section of APF calculations in the Analytical menu section for details on how these values are used for the calculation of APFs.
The APF calculations are in units of counts per second for the peak intensities and area counts per second divided by spectrometer range (between the low off-peak and high off-peak positions) for the integrated intensities (counts per second per spectrometer unit). Both the peak and integrated intensities are background corrected using the currently selected background fit type.
Centroid Calculations
The Model Background dialog will also calculate the centroid of the displayed wavescan. The program will fit the wavescan intensities that are within the currently displayed x-axis zoom range (min to max) of the Graph dialog to a parabola (2nd order polynomial), maxima or Gaussian centroid. Therefore the user should zoom the wavescan to display only the top portion of the wavescan peak for best results. The parabolic peak centroid is calculated using the following equation:
Where:
is the
centroid of the peak
is the
first fit coefficient (intercept)
is the
second fit coefficient (slope)