Mass, monoisotopic

Monoisotopic mass The mass of an ion calculated using the exact mass of the most abundant isotope of each element in the formula (e.g., C = 12.0000, O = 15.9949). 

X 12 = 72 (Multiply 6 carbon atoms by monoisotopic mass of carbon.)... 

Showing the monoisotopic masses of fragments MH+ of /i-lactoglobulin A cysteine residues are shown in bold script, i.e. cysteine-C aromatic residues are underlined, i.e. phenylalanine-F, tyrosine-F, and tryptophan- mIz expected for singly charged species. 

Thr28-Gin27-Vai28-Gin2 -Asp8°-Giy -Lys32 Monoisotopic mass = 774.39 Da... 

High mass accuracy (<5 ppm selectivity and elemental composition based on monoisotopic masses)... 

Da of the monoisotopic masses, high sensitivity (down to 20fmolp,L 1), and the absence of any fragmentation, are important advantages for a L-ToF system. The main characteristics of MALDI-ToFMS, as applied directly to polymer/additive dissolutions, are summarised in Table 9.7. 

Senko, M. W. Beu, S. C. McLafferty, F. W. Determination of monoisotopic masses and ion populations for large biomolecules from resolved isotopic distributions. J. Am. Soc. Mass Spectrom. 1995, 6,229-233. 

Table 2.5 Natural isotopic abundances and monoisotopic masses of common elements...

Accurate Mass An experimentally determined mass of an ion that is used to determine an elemental formula. For ions containing combinations of the elements C, H, N, O, P, S, and the halogens, with mass less than 200 Da, a measurement with 5 ppm uncertainty is sufficient to uniquely determine the elemental composition. See also related entries on average mass dalton molar mass monoisotopic mass nominal mass unified atomic mass unit. 

Mass See entries on accurate mass average mass dalton molar mass molecular weight monoisotopic mass nominal mass unified atomic mass unit. 

Comment The same problem as for monoisotopic mass immediately arises for compounds containing elements such as Fe or B. See discussion in entry monoisotopic mass. 

Name Formula Monoisotopic Mass (Average) Methylated Monoisotopic Mass of Derivatives Deutero- methylated Acetylated Deutero- acetylated... 

Gly21—Asn22 -1 le23 - Thr24 - Phe25 Monoisotopic mass = 550.28 Da... 

The exact mass of the most abundant isotope of an element is termed monoisotopic mass. [3] The monoisotopic mass of a molecule is the sum of the monoisotopic masses of the elements in its empirical formula. As mentioned before, the monoisotopic mass is not necessarily the naturally occurring isotope of lowest mass. However, for the common elements in organic mass spectrometry the monoisotopic mass is obtained using the mass of the lowest mass isotope of that... 

The exact mass of a positive ion formed by the removal of one or more electrons from a molecule is equal to its monoisotopic mass minus the mass of the elec-tron(s), ffje. [1] For negative ions, the electron mass (0.000548 u) has to be added accordingly. 

As we have already seen, the isotopic mass also is the exact mass of an isotope. The isotopic mass is very close but not equal to the nominal mass of that isotope (Table 3.1). Accordingly, the calculated exact mass of a molecule or of a mono-isotopic ion equals its monoisotopic mass (Chap. 3.1.4). The isotope C represents the only exception from non-integer isotopic masses, because the unified atomic mass [u] is defined as of the mass of one atom of nuclide C. 

In the retesting and deconvolution phase of the procedure new compound mixtures were made based on the results of primary screening. These contained from nine to 14 compounds and no monoisotopic mass redundancy. Since most mass spectrometric peaks picked as hits in the primary screen contain more than one compound, and only one compound per peak is likely to be a binder, the nonmass redundant retest mixtures are unlikely to contain more than a few bona fide ligands, so once again target excess is maintained. Both the initial (round zero,... 

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