Base peaks, scaling

Let IM be the intensity of a peak at mass M, normalized to the highest peak in the spectrum (the base peak with intensity 100%). A spectral feature Xj is a function of one or several peak intensities and is scaled to the range 0-100. Spectral features can be used—eventually together with original peak intensities—to characterize a mass spectrum of a compound. The typical parameters given here are for electron impact mass spectra. 

Scaling to a base peak. In some forms of measurement, such as mass spectrometry (e.g. LC-MS or GC-MS), it is possible to select a base peak and scale to this for... 

The standard low-resolution mass spectrum (Fig. 30.3) is computer generated, which allows easy comparison with known spectra in a computer database for identification. The peak at the highest mass number is the molecular ion (M ), the mass of the molecule minus an electron. The peak at RA = 100%, the base peak, is the most abundant fragment in the spectrum and the computer automatically scales the spectrum to give the most abundant ion as 100%. The mass spectrum of a compound gives the following information about its chemical structure ... 

The most abundant ion peak in many compounds in the methamphetamine family is found at 58 amu. Mass spectra are processed by assigning the largest peak (called the base peak) a value of 100 and scaling all other peaks to that value. Consequently, many minor peaks may be all but lost. Removing the base peak and renormalizing the... 

The label 50 indicates that the intensity scale ends at 50% relative intensity and is subdivided in 10% steps. In these cases, the height of the base peak has to be doubled to bring it to 100%. All spectra represent positive ions only. 

Example El vs. methane reagent gas PICI spectrum of methionine. The comparison shows greatly reduced fragmentation in the PICI spectrum (Fig. 7.4). Only small intact molecules such as NH3, HCOOH, and MeSH are eliminated from the [Mh-H]" ion, m/z 150, which yields the base peak. In addition, the PICI spectrum perfectly reveals the isotopic pattern that indicates the presence of sulfur. The horizontal line (Fig. 7.4b) means that this range was not acquired in the PICI spectrum as to keep the spectrum free from reactant ion signals. The spectra were, however, plotted on the same m/z scales to simplify the comparison. 

Figure 3.16a shows the storage and loss components of the compliance of crystalline polytetrafluoroethylene at 22.6°C. While not identical to the theoretical curve based on a single Voigt element, the general features are readily recognizable. Note that the range of frequencies over which the feature in Fig. 3.16a develops is much narrower than suggested by the scale in Fig. 3.13. This is because the sample under investigation is crystalline. For amorphous polymers, the observed loss peaks are actually broader than predicted by a...

Application of the Baker-Strehlow method for evaluating blast effects from a vapor cloud explosion involves defining the energy of the explosion, calculating the scaled distance (/ ), then graphically reading the dimensionless peak pressure (Ps) and dimensionless specific impulse (i ). Equations (4.41) and (4.42) provide the means to calculate incident pressure and impulse based on the dimensionless terms. 

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