Molecular mass measurement

Another type of ion is formed almost uniquely by the electrospray inlet/ion source which makes this technique so valuable for examining substances such as proteins that have large relative molecular mass. Measurement of m/z ratios usually gives a direct measure of mass for most mass spectrometry because z = 1 and so m/z = m/1 = m. Values of z greater than one are unusual. However, for electrospray, values of z greater than one (often much greater), are quite coimnonplace. For example, instead of the [M + H]+ ions common in simple Cl, ions in electrospray can be [M + n-H]- where n can be anything from 1 to about 30. 

Naito, Y. Ishikawa, K. Koga, Y. Tsuneyoshi, T. Terunuma, H. Arakawa, R. Molecular mass measurement of polymerase chain reaction products amplified from human blood DNA by electrospray ionization mass spectrometry. Rapid Commun. Mass Spectrom. 1995,9,1484-1486. 

Zubarev, R. A. Hakansson, P. Sundqvist, B. Accuracy requirements for peptide characterization by monoisptopic molecular mass measurements. Anal. Chem. 1996,68,4060 1063. 

Limbach, P.A. Crain, P.F. McCloskey, J.A. Molecular Mass Measurement of Intact Ribonucleic Acids Via ESI Quad-rapole MS. J. Am. Soc. Mass Spectrom. 1995, 6, 27-39. 

Experimental mechanistic studies of such reactions are in their early days. However, it is clear that proper understanding will rely on the prior isolation of the organolithium reagent, rather than on its production, then use, in situ. Thereafter, the reagent needs to be identified (e.g., RLi or RLi xL ) and characterized structurally, in the solid by X-ray diffraction and, perhaps more importantly, in solutions (by colli-gative molecular mass measurements and multinuclear NMR spectroscopic studies) in which it will be used. 

Chemists now routinely use open-access LC/MS in the same way that they previously used TLC to monitor reaction mixtures for the desired product and to optimize reaction conditions. In practice, medicinal chemists require only molecular mass data and are comfortable with a variety of ionization methods to obtain this information. However, confidence in the actual method and procedure is a requisite. Today, molecular mass measurement has quickly become a preferred means of structure confirmation over NMR and IR during the early stages of synthetic chemistry activities, where sample quantities are limited. 

To avoid the inconvenience of the TFA (decrease sensitivity) during MS, if molecular mass measurements are performed on fractions that may contain traces of TFA, the sample has to be desalted and concentrated onto a Ci8 Zip-Tip. Elution of the peptide(s) will then be performed by 50% aqueous acetonitrile supplemented with 1 % formic acid. 

Diorganotetrahalotellurates were prepared by combining diaryl tellurium dihalides, pentamethylene tellurium diiodide or tetramethylene tellurium diiodide with onium halides. These compounds were found to be 2 1 electrolytes by conductivity and molecular mass measurements. ... 

Inspection of fracture surfaces of photodegraded polymers often reveals the presence of a smooth brittle zone near to the surface and a much more ductile fracture in the interior. The brittle zone depth often corresponds to that of the highly degraded depth obtained by FTIR or molecular mass measurements. 

The composition and structure of the compounds XLV - XLVn were determined by means of elementary analyses, molecular mass measurements, IR and NMR spectral data (see Table 6.7). 

The emphasis so far has been placed on processes which, by their random nature, lead to polydispersity. For some fundamental studies and technological applications, block copolymers ionic initiation and living polymer techniques have been used [3.68], [3.69]. The growing polymer chains remain active until they are deliberately quenched. These processes yield polymers that are monodisperse with respect to molecular mass. Measurements made on dispersions, sterically-stabilized with almost monodisperse block copolymers, yield results which are more readily interpreted. 

Cis-1,4, Mn = 650 method = molecular mass measurements and biomass inoculum = acenitobacter... 

Molecular mass measurement of large biological compounds Simultaneous separation and detection of complex nfixtures of biological compounds... 

One of the most important pieces of information required to elucidate the molecular structure of an unknown organic compound is its molecular mass, which provides a window within which the elemental composition and the final structure of the compound must fit. Therefore, the first essential step to identifying a compound is to measure its molecular mass by determining the m/z value of the molecular ion. Molecular mass measurements can be performed at either low or high resolution. A low-resolution measmement provides information about the nominal mass of the analyte, and its elemental composition can be also determined for low-molecular-weight compounds from the isotopic pattern. From a high-resolution mass spectrum, the accurate molecular mass can be determined, from which it is also feasible to deduce the elemental composition. Chemists who work with synthetic compounds and natural products rely heavily on the exact mass measurement data for structmal assignment. This value is acceptable in lieu of the combustion or other elemental analysis data. An acceptable value of the measured mass should be within 5 ppm of the accmate mass [1]. As shown below, the mass measurement error is reported either in parts per million (ppm) or in millimass units (mmu). 

Molecular Mass Measurements at Low-Mass Resolving Power... 

Reduction-alkylation of proteins. The molecular mass measurement of the target protein before and after this step provides information on the number of cysteine residues and disulfide bonds. 

Top-down proteomics. This strategy deals with intact protein molecules no proteolytic cleavage is performed [41], It involves the accurate molecular mass measurement of the intact protein nsing high-resolution mass spectrometry within 2 Da, followed by a molecular mass database search. The identity of... 

Comparative Peptide Mapping This procedure is used when the protein is cleaved with specific cleaving agents and the sequence of the protein is known. A simple molecular mass measurement of the peptides in a protein digest will identify the position of a disulfide bond in the protein. 

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