Peak fitting software

To demonstrate calibration linearity and transferability using a fiber-optic probe and simple peak-area methods, the solution spectra of four solutions of phenylisocyanate in acetone were used. The mid-infrared spectrum of most isocyanates are characterized by a sharp band, sometimes exhibiting shoulders, at 2250-2285 cm which is assigned to the asymmetric stretch of the -N C=0 group. In the spectra of acetone solutions of phenylisocyanate, this band appears at 2261 cm with a substantial shoulder at 2283 cm. Figure 1 shows an expanded view of the band, displayed in a screen shot from the GRAMS peak-fitting software with two Lorentzian peaks fitted at 2261 and 2283 cm. ... 

Modem pRS systems are accompanied with powerful spectral acquisition and analysis software, which enables the creation of ID (cross section), 2D, and 3D maps of various features from the ID, 2D, or 3D array of spatially resolved Raman spectra. Various features that can be routinely mapped include intensity variations of specific peaks (by plotting the user-defined peak intensity or integrated area under the peak), intensity ratio of two different bands, peak position (by user-defined peak fitting routines such as Gaussian, Lorentzian), and peak widths. The obtained images can be further processed to highlight the spatial variations of the acquired spectra. For example. Boolean maps, which present a binary... 

A simplified approach to peak fitting is to use a suitable analytical function to approximate the measured peak. As in the previous section, the function parameters are adjusted to obtain an optimal fit to the experimental data. In a next step the adjusted function (or its parameters) is used to calculate the first and second moment. This procedure may, for example, help to overcome the inaccuracy of moment analysis in case of asymmetric peaks (Chapter 2.7). It also offers the benefit that standard software such as spread sheets can be used instead of special parameter estimation systems. 

XPS analyses were performed 1 day after the plasma treatment on a Leybold LHS 12 XPS spectrometer ( Institut des Materiaux , CNRS, Nantes, France) with a Mg Ka X-ray soixrce of energy 1.2536 keV). The analyzed depth is approximately 10 nm. The number of scans was 5 for the wide-scan spectra and 15 for the high-resolution spectra. All spectra were referenced to the Cis peak for hydrocarbon, which is assigned a value of 285 eV. The data were collected with a Hewlett-Packard 2436 E computer, and peak fitting was done using Peak Fit 4.0 software (Jandel Scientific). The full width at half maximum (FWHM) was maintained constant, and the peak shape was chosen with Gaussian/Lorentzian (1/1) curve fitting. 

Detailed spectra were processed with CasaXPS software (V2.3.12, Casa Software Ltd., UK). An iterated Shirley-Sherwood background subtraction was applied before peak fitting using a linear-least-squares algorithm. Minor charging was observed and corrected by referencing the aliphatic carbon to 285.0 eV. Details on the curve-fitting parameters, whieh have been measured on reference compounds, have been pubUshed elsewhere [10, 11],... 

The intensity of a resonance can be measured in several ways (1) peak heights and areas obtained from the standard software supplied by the spectrometer manufacturer, (2) peak heights measured by hand, (3) peaks cut and weighed from the plotted spectrum, and (4) peaks fitted to a Lorentzian line shape. For flat baselines, intensity measurements are generally straightforward. However, in the event of curved baselines the measurements are somewhat uncertain and manual measurements are generally more reliable than intensity values obtained from computer software. 

ToF-SIMS has been used in a similar manner, in the work of Shimizu et al. (2010) to identify the specific interaction between aluminum and polymeric methylene diphenyl diisocyante (PMDI). A series of ToF-SIMS spectra from the region of nominal mass m/z = 102 u is shown in Fig. 10.16, and the spectra have been peak-fitted which is not a standard practice in ToF-SIMS (first demonstrated by Abel et al. 2009), although it is readily accomplished using standard XPS software such as CasaXPS (CasaXPS 2009). These range from a concentrated solution ( Fig. 10.16a, 5 v/v%) through to a dilute solution and the bare aluminum substrate ( Fig. 10.16e and/j respectively). For the two most concentrated solutions Pig- and b)... 

The summation runs over all the absorption bands (with wavenumber Vq and experimental dipole strength Oexp) which contribute to the complex band structure. Y, D xp total dipole strength of the complex band. In practice, v is determined by curve-fitting software by placing a line shape function under the complex band. Vq is equal to the sum of the peak maxima Vq weighted by the fractional contribution Xj (0 1, X, x,- = 1)... 

It seen that the de-convolution is likely to be successful as the position of the peak maximum, and the peak width, of the major component is easily identifiable. This would mean that the software could accurately determine the constants in the Gaussian equation that would describe the profile of the major component. The profile of the major component would then be subtracted from the total composite peak leaving the small peak as difference value. This description oversimplifies the calculation processes which will include a number of iteration steps to arrive at the closest fit for the two peaks. 

The other plots are made with the software TABLECURVE. The special function F2 used there is a log-normal relation and F3 is a sine-wave function. Usually a ratio of low degree polynomials also provides a good fit to bell-shaped curves here five constants are needed. The Gamma distribution needs only one constant, but the fit is not as good as some of the other curves. The peak, especially, is missed. 

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