![]() įor a spectrum that is digitized at constant intervals, Vcg can be computed by the following summation In practice, the wavenumber of the maxima of bands in the spectra of condensed-phase spectra measured at a resolution of 2 or 4 cm should only be reported to 1 cm. Under these conditions simple peak-picking algorithms would not readily detect band shifts of about 0.5 cm. For example, in a typical spectrum measured at 4-cm resolution, data points are typically computed at 2-cm intervals. The actual band center may be considerably displaced from the maximum data point. The use of the maximum data point for the wavenumber position of a band is suitable only for noncritical information. It is not uncommon for these values to be reported to four or five decimal places, as this is how well the wavenumber of each datum is recorded however this number of digits is well beyond the realistic accuracy of most experiments. The result that is reported as the peak wavenumber is frequently the wavenumber value of the maximum discrete point, which rarely corresponds to the exact center of the band. Peak areas are to be preferred for such analyses, as areas better compensate for matrix effects (interactions). This may be of use for quantitative work, although it remains preferable to analyse peaks personally when quantitation is required. Coupled with peak-picking, there is usually a facility to store peak heights and areas in the same data file. This is a very useful facility and greatly eases the task of interpretation. Most operating software offers the facility to pick out the peak maxima in the spectrum and store the results in a file and/or label the peaks on the paper hardcopy. During this operation the cursor will only move to marked peaks. The buttons in the peak picking button panel have several functions Įdit Cursor Allows you to edit (delete, add multiplicity information) currently displayed peak labels. Furthermore, the Interpolation and Multiplicity mode can be set which increases the accuracy of the peak picking and lists the multiplicity information respectively. In this dialog box the Peaks sign, the Peaks Label and the parameter PC, which determines the sensitivity of the peak picking algorithm may be specified. Activating this menu option switches the button panel into the Peak Picking mode, the mouse cursor to Peak Picking Zoom mode and opens a dialog box (Fig. The Peak Picking option in the Analysis pull-down menu allows peak picking in an interactive way. Peak picking is usually performed to measure chemical shifts (in ppm relative to a reference peak in the spectrum) or to measure line separations (in Hz) in multiplets in order to calculate or at least to estimate coupling constants. ![]()
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