783620H / 1013 6. ANALYSIS METHODS
All peaks found by the peak search routine and not in the library are included in the deconvolution regardless of the sensitivity setting, unless all the deconvolution candidates are unknown peaks with uncertainty greater than the sensitivity setting, in which case the region is ignored.
6.5.1. Defining a Multiplet Region for Deconvolution
After a list of peaks is determined from the library-directed and Mariscotti peak searches, multiplets are identified. Note that peaks which are found by the Mariscotti peak search but do not pass the sensitivity (peak cutoff) test are flagged for further multiplet consideration. For each located peak, the energy of the next peak is checked to see if it is less than or equal to 3.08 times the FWHM of the peak currently being processed. If so, the two peaks are marked as a multiplet.
The energy of successive peaks is checked, using the same criteria, to determine if they belong in the multiplet. After the last peak in the multiplet is identified, the multiplet is flagged for peak deconvolution.
Because a multiplet identified in this way might contain a combination of library peaks and unidentified peaks, the analysis engine processes it as follows:
! If library energies are less than 10 eV apart, the lowest-energy peak is included in the deconvolution and the other peaks within 10 eV are set to zero.
! If all the peaks in the multiplet are unidentified (i.e., not listed in the library) and do not meet the sensitivity criterion, the entire region is ignored.
The width of the multiplet region is from 1.5 times the FWHM below the lowest peak to
1.5 times the FWHM above the highest-energy peak (Fig. 243).
6.5.2. Establishing Multiplet Background
Three background types are used for multiplets: stepped, parabolic, and straight-line. Selection of the background type depends on the shape of the peak background.
1) Stepped background is used if the slope of the peak background across the peak area is less than the slope of the background adjacent to the high-energy side of the peak. That is, if the background under the peak is declining faster than the background above the highest-energy peak in the background, the stepped background is selected; see Fig. 244.
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Fig. 243. Background for Multiplets.
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Fig. 244. Stepped Background.
2) Parabolic background is selected if:
! The background on the low-energy side of the multiplet is less than the background on the high-energy side.
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