Molecular weight by mass spectrometry

One way to determine the number of acidic hydrogens in a molecule is to treat the compound with NaOD in D20, isolate the product, and determine its molecular weight by mass spectrometry. For example, if cyclohexanone is treated with NaOD in DzO, the product has MW = 102. Explain how this method works. 

Whatever the reasons for the above observations, introduction of a substituent of low ionization potential is a useful addition to the methods available for increasing the intensities of molecular ions, thereby aiding the determination of molecular weights by mass spectrometry. 

In an attempt to isolate a factor responsible for stimulating hepatocyte growth. Nelson et al. (31) used a PolyHEA column to fractionate an extract of liver by size. The active fraction eluted at a position corresponding to approximately 200 Da the actual molecular weight (electrospray mass spectrometry ES-MS) was 215 Da. The compound of interest proved to be glycerophosphorylethano-lamine. 

The presence of the P4 molecule was indicated by osmometric molecular weight determinations, mass spectrometry, and by the easy displacement, even at -78°C, of the intact P4 unit by carbon monoxide or phosphane ligands. The infra-red and Raman spectra showed bands attributable to a bound P4 molecule under 3 or Cg... 

Polymers are not easily converted to gas-phase ions but this is a requirement for compounds analyzed by mass spectrometry. Despite this difficulty, mass spectrometry has been utilized to study various aspects of polymers polymers can be characterized - among others - with respect to their chemical composition, to their end groups, and to their molecular weight. Moreover, mass spectrometry can be used to study polymer surfaces. 

It is also possible to estimate the molecular weight of a protein by means of gel filtration, or from measurement of its rate of migration through an electrophoresis gel (gel electrophoresis), in comparison with a series of standards of known molecular weight. An absolute and very accurate means of determining protein molecular weights is mass spectrometry. 

Amines have odd numbered molecular weights which helps identify them by mass spectrometry Fragmentation tends to be controlled by the formation of a nitrogen stabilized cation... 

The analysis of penicillins by mass spectrometry (qv) has developed with the advent of novel techniques such as fast atom bombardment. The use of soft ionization techniques has enabled the analysis of thermally labile nonvolatile compounds. These techniques have proven extremely valuable in providing abundant molecular weight information from underivatized penicillins, both as free acids and as metal salts (15). 

Properties of luciferin precursors. About one dozen of the luciferin precursors of M. citricolor isolated by HPLC had a strong tendency of isomerization, as mentioned above. Their molecular weights could not be established by mass spectrometry, which is probably due to isomerization, although they appear to be in a range of 300-600. The precursors showed an absorption peak at about 369 nm in methanol and aqueous acetonitrile (Fig. 9.13). According to an NMR study, all precursors probably contain the following common partial structure (personal communication from Dr. H. Nakamura, 1998). 

Verification of the molecular weight of thiirene dioxides by mass spectrometry, employing the conventional electron-impact (El) ionization method, has been unsuccessful due to the absence or insignificant intensity of molecular ion peaks in their mass spectra. The base peak is rather characteristic, however, and corresponds to the formation of the disubstituted acetylene ion by loss of sulfur dioxide91 (equation 3). 

The mass spectrum produced should provide unambiguous molecular weight information from the wide range of compounds amenable to analysis by HPLC, including biomolecules with molecular weights in excess of 1000 Da. The study of these types of molecule by mass spectrometry may be subject to limitations associated with their ionization and detection and the mass range of the instrument being used. 

Analysis of polymer additives by mass spectrometry has, for the most part, been limited to molecular weight determination of the solvent-extracted components [4,254], Field desorption is a good ionisation... 

The cluster Co4(CO)2Cp4 has been obtained according to Eq. (6). The molecular weight has been confirmed by mass spectrometry, and infrared spectra are consistent with the carbonyls being triply bridging237, 238. ... 

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