Most abundant mass

The quadrupole mass filter is the most abundant mass analyser today and RF-only multipoles are used as transmission devices/collision regions in various instrumental configurations. The mass filter is used extensively as a stand-alone mass analyser and as an analyser in multistage mass spectrometers. 

In this method, chromium is extracted and preconcentrated from seawater with trifluoroacetylacetone [H(tfa)] which complexes with trivalent but not hexavalent chromium. Chromium reacts with trifluoroacetylacetone in a 1 3 ratio to form an octahedral complex, Cr(tfa)3. The isotopic abundance of its most abundant mass fragment, Cr(tfa)2 was monitored by a quadrupole mass spectrometer. 

The position of the most intensive peak of an isotopic pattern is termed most abundant mass. [3] For example, the most abundant mass in case of C120 is 1441 u corresponding to M+1 (Fig. 3.2). The most abundant mass is of high relevance if large ions are concerned (Chap. 3.4.3). 

The calculation of isotopic patterns of molecules of several 10 u is not a trivial task, because slight variations in the relative abundances of the isotopes encountered gain relevance and may shift the most abundant mass and the average mass up or down by 1 u. In a similar fashion the algorithm and the number of iterations employed to perform the actual calculation affect the final result. [16]... 

This means that for a protein of mass >10 kDa there will be a confusing array of peaks in the mass spectrum and it may be difficult to pick out the relatively minor "monoisotopic" peak that arises from molecules containing only 12C, 1H, 14N, leO, and 32S. In fact, the peak representing the most abundant mass will be a few mass units higher than the monoisotopic peak.215 216 (see Study Question 15). New computer programs have been devised to assist in the analysis. Use of 13C and 15N-depleted nutrients also extends the applicability of mass spectrometry.217... 

The capillary HPLC separation from a selected protein spot provides a base-peak profile shown in Figure 6.2A. The base-peak profile is similar to a total ion current (TIC) profile, but it contains only the most abundant mass spectral peak in each scan. The chromatogram is simplified and the contributions from background ion abundances are eliminated, resulting in an enhanced signal-to-ion ratio for an improved visualization of data. The molecular mass for each component is labeled along with corresponding amino acid residues. This format provides a comprehensive approach for peak selection and peptide identification. 

Atoms that have the same atomic number (Z) but different atomic mass numbers (A) are termed isotopes [1]. Isotopes are classified into atoms that are unstable and decay by emission of radiation to stable products (radioisotopes) and those that have never been observed to decay (stable isotopes). Most of the elements associated with organic compounds possess naturally occurring stable isotopic variants. Stable isotopes frequently encountered in the course of pharmacokinetic and drug-metabolism studies and their natural abundances, relative to the most abundant mass, are listed in Table 1 [2,3]. 

Element Most abundant mass (100%) Stable isotope Relative natural abundance (%)... 

Figures 2 and 4-7 show the percentage abundance of the masses referred to the most abundant species observed. This is, for example, 73 in the case of Si(CH3)4 and [(CH3)3Si—CH2]2Si(CH3)2, 145 (molecular mass — 15) for [(CH3)3Si]2CH2, and 201 (molecular mass — 103) for the Si-methylated compound [(CH3)3Si—CH2—Si(CH3)2]2CH2. The mass numbers and percentage abundances of the ions from the linear compounds are summarized in Fig. 2. The ions which occur result, as a rule, from cleavage of the Si—C bond. Both CH2Si(CH3)3 and CH3 groups are split off and this will account for the greater part of the observed masses. For the mass spectra from carbosilanes of the general formula Si C3n+iH8n+4, the most abundant masses of the ions formed may be represented by ...

The spectrum of [(CH3)3Si]2C=CH2 differs from the others in that the molecule ion gives the most abundant mass, showing the greater stability of compounds with a double bond. This effect is also found in the spectra of (CH3)sSiCH=CH2 and C8H6Si(CH3)3. It is seen from the above that the different types of compound studied have characteristic mass spectra, which also reveal the influence of substituents on the stability of the structure. Mass spectrographic investigations offer a route to the analysis of mixtures of such compounds and yield valuable information relating to other questions. 

Table 1.6 Substances identified by the electronic library (Wiley) in the Py-GC-MS analysis of Kraton 1107 with the eight most abundant masses and their relative intensities according to the Eight Peak Index (Mass Spectrometry Data Center) ...

Retention time (min) Substance Eight most abundant masses (relative intensities)... 

A compound containing only C, H, and Cl was examined in a mass spectrometer. The highest mass peak seen corresponds to an ion mass of 52 amu. The most abundant mass peak seen corresponds to an ion mass of 50 amu and is about three times as intense as the peak at 52 amu. Deduce a reasonable molecular formula for the compound and explain the positions and intensities of the mass peaks mentioned. Hint Chlorine is the only element that has isotopes in comparable abundances 17CI 75.5 percent 17CI 24.5 percent. For H, use jH for C, use sC.)... 

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