Mass spectrum definition

The strength of the ion current relates to the number of ions per second arriving at the collector plate, and a mass spectrum can be regarded as a snapshot of the current taken over a definite period of time. Because of the finite time taken to produce a mass spectrum, it is a record of the abundances of ions (often mistakenly called intensities of ions). 

Resolution 10% valley definition, m/Am. Let two peaks of equal height in a mass spectrum at masses m and m/Am be separated by a valley that at its lowest point is just 10% of the height of either peak. For similar peaks at a mass exceeding m, let the height of the valley at its lowest point be more (by any amount) than 10% of either peak height. Then the resolution (10% valley definition) is m/Am. It is usually a function of m therefore, m/Am should be given for a number of values of m. 

Resolution (10% valley definition) Let two peaks of equal height in a mass spectrum at masses m and (m - Am) be separated by a valley that at its lowest point is 10% of the height of the peaks. 

The X-ray spectra of niobium have been investigated.4 Aston was unable to obtain a definite mass spectrum of the metal.5 The arrangement of the electron groups in the atom has been considered by Lesshdm and Samuel.4 Niobium is not radioactive.7... 

Some of the early studies reported abnormal fragmentation patterns when polyatomic molecules were seeded in argon. It was speculated that heteroclusters, such as Ar Xra, are the neutral precursors for the various ions observed in the cluster mass spectrum. Our study of the argon/methanol coexpansions showed that the CMS is definitely affected by the choice of carrier gas, as well as the energy... 

L. C16H29NO. Cochromatographs with another alkaloid, and because of this a definitive mass spectrum could not be obtained. Occurs mainly as the 0-acetate (73). 251L O-acetate. C18H31NO2, —,—, ion trap, m/z 293(<1), 250(18), 222(32), 176(77), 148(40), 134(22), 84(80). Infrared data (73). The infrared spectrum is typical for homopumiliotoxins, as is the m/z 84 fragment. 

The gas phase pjnrolysis of alkyl hahdes has been extensively reviewed 58>, and in general the unimolecular gas phase reactions of alkyl halides parallel their reactivity in a mass spectrometer. For example, ethylchloride yields ethylene and HCl on thermolysis 5 >, and the ethylene ion in the mass spectrum of ethyl chloride is significantly more intense than the molecule ion. 1,2-dichloroethane also eliminated HCl thermolytically and the corresponding ion is the base peak in its mass spectrum. Elimination of HCl is also common to the mass spectra and thermochemistry of chloroprene dimers.Although in this case the major ion at mje 91 had no definite analog in the thermochemistry. This is probably due to the fact that mje 91 was a tropylium ion which would not be stabihzed as a neutral. 

In addition to F, Cl and F , the negative ions mass spectrum given by Ahnell and Koski ) indicates a peak at M/z = 27 and hints of the presence of CF and C1F ions. Possibly other species also are present, but the low resolution of the mass spectmm shown precludes any attempt at definitive assignment by this author. The presence of the M/z = 27 ion (possibly HCN ) with a relative abundance of about 2-3 % in their spectrum is not commented on by Ahnell and Koski. 

Because mass-spectral fragmentation patterns are usually complex, it s often difficult to assign definite structures to fragment ions. Most hydrocarbons fragment in many ways, as the mass spectrum of hexane shown in, Figure 12.4 demonstrates. The hexane spectrum shows a moderately abundant molecular ion at m/z = 86 and fragment ions at m/z - 71, 57,43, and 29. Since all the carbon-carbon bonds of hexane are electronically similar, all break to a similar extent, giving rise to the observed ions. 

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