Mass interpretation

J. P. Vigier, New non-zero photon mass interpretation of the Sagnac effect as direct experimental justification of the Langevin paradox, Phys. Lett. A 234(2), 75-85 (1997). 

Hydrogen sulfide gas, H2S, burns in oxygen to give sulfur dioxide, SO2, and water. Write the equation for the reaction, giving molecular, molar, and mass interpretations below the equation. 

The unique adduct ions (M -1- C2H5) = (M -1- 29) and (M -I- CjHj)" = (M -I- 41) formed by the methane cluster confirm the molecular mass interpretation. These adduct ions are easily seen as a mass difference of 28 resp. 40 from the protonated molecular ion (M+H)". ... 

Adduct formation with NH4" occurs with substances where the proton affinity differs little from that of NHg and can be used to confirm the molecular mass interpretation. In these cases the formation and addition of higher (NH3), clusters is observed with instruments with threshold pressures of... 

The Mathieu equation for the quadnipole ion trap again has stable, bounded solutions conesponding to stable, bounded trajectories inside the trap. The stability diagram for the ion trap is quite complex, but a subsection of the diagram, correspondmg to stable trajectories near the physical centre of the trap, is shown in figure Bl.7.15. The interpretation of the diagram is similar to that for tire quadnipole mass filter. 

To enable an atomic interpretation of the AFM experiments, we have developed a molecular dynamics technique to simulate these experiments [49], Prom such force simulations rupture models at atomic resolution were derived and checked by comparisons of the computed rupture forces with the experimental ones. In order to facilitate such checks, the simulations have been set up to resemble the AFM experiment in as many details as possible (Fig. 4, bottom) the protein-ligand complex was simulated in atomic detail starting from the crystal structure, water solvent was included within the simulation system to account for solvation effects, the protein was held in place by keeping its center of mass fixed (so that internal motions were not hindered), the cantilever was simulated by use of a harmonic spring potential and, finally, the simulated cantilever was connected to the particular atom of the ligand, to which in the AFM experiment the linker molecule was connected. 

In contrast to IR and NMR spectroscopy, the principle of mass spectrometry (MS) is based on decomposition and reactions of organic molecules on theii way from the ion source to the detector. Consequently, structure-MS correlation is basically a matter of relating reactions to the signals in a mass spectrum. The chemical structure information contained in mass spectra is difficult to extract because of the complicated relationships between MS data and chemical structures. The aim of spectra evaluation can be either the identification of a compound or the interpretation of spectral data in order to elucidate the chemical structure [78-80],... 

Alkylidenehydrazinothiazoles (297) can be prepared either from 2-hydrazinothiazoles (549) or by direct heterocyclization (527). Their characteristic infrared bands have been reported (550). The main mass spectrometric peaks of (4-coumarinyl-2-thiazolyl)hydrazone (302) (Scheme 179) (134, 551) are situated at mle = 361. 244, 243, 118, 216, 202, 174, 117 the proposed interpretation of the fragmentation pattern should, however, be reconsidered. Scheme l80 summarizes some representative reactions of this class of compounds. 

Knowing what to look for with respect to isotopic clusters can aid in interpreting mass spectra How many peaks would you expect to see for the molecular ion in each of the following compounds At what m/z values would these peaks appear (Disregard the small peaks due to and )... 

As we have just seen interpreting the fragmentation patterns m a mass spectrum m terms of a molecule s structural units makes mass spectrometry much more than just a tool for determining molecular weights Nevertheless even the molecular weight can provide more information than you might think... 

Interpreting the mass spectra of sulfur compounds is aided by the observation of an M+2 peak because of the presence of the mass 34 isotope of sulfur The major cleav age pathway of thiols is analogous to that of alcohols... 

A very good general survey for interpreting mass spectral data is given by R. M. Silverstein, G. C. Bassler, and T. C. Morrill, Spectrometric Identification of Organic Compounds, 4th ed., Wiley, New York, 1981. 

To increase the number of theoretical plates without increasing the length of the column, it is necessary to decrease one or more of the terms in equation 12.27 or equation 12.28. The easiest way to accomplish this is by adjusting the velocity of the mobile phase. At a low mobile-phase velocity, column efficiency is limited by longitudinal diffusion, whereas at higher velocities efficiency is limited by the two mass transfer terms. As shown in Figure 12.15 (which is interpreted in terms of equation 12.28), the optimum mobile-phase velocity corresponds to a minimum in a plot of H as a function of u. 

The mass spectrum is characteristic for different substances and can be used like a fingerprint to identify a substance, either by comparison with an already known spectrum or through skilled interpretation of the spectrum itself (Figure 3.2). 

However, interpretation of, or even obtaining, the mass spectrum of a peptide can be difficult, and many techniques have been introduced to overcome such difficulties. These techniques include modifying the side chains in the peptide and protecting the N- and C-terminals by special groups. Despite many advances made by these approaches, it is not always easy to read the sequence from the mass spectrum because some amide bond cleavages are less easy than others and give little information. To overcome this problem, tandem mass spectrometry has been applied to this dry approach to peptide sequencing with considerable success. Further, electrospray ionization has been used to determine the molecular masses of proteins and peptides with unprecedented accuracy. 

Data reduction. The process of transforming the initial digital or analog representation of output from a spectrometer into a form that is amenable to interpretation, e.g., a bar graph, a table of masses versus intensities. 

Lee, T.A., A Beginner s Guide to Mass Spectral Interpretation, Wiley, Chichester, U.K., 1998. 

McLafferty, F.W, Interpretation of Mass Spectra, University Science Books, 1996. 

Snyder, A.P., Interpreting Protein Mass Spectra A Comprehensive Resource, American Chemical Society, Washington, D.C., 2000. 

The right-hand side is now a pure number and, if we wish to plot mass, in grams, against, say, volume on a graph we label the mass axis m/g so that the values marked along the axis are pure numbers. Similarly, if we wish to tabulate a series of masses, we put m/g at the head of a column of what are now pure numbers. The old style of using m(g) is now seen to be incorrect as, algebraically, it could be interpreted only as m x g rather than m g, which we require. 

The molecular composition of sulfur vapor is a complex function of temperature and pressure. Vapor pressure measurements have been interpreted in terms of an equiHbtium between several molecular species (9,10). Mass spectrometric data for sulfur vapor indicate the presence of all possible molecules from S2 to Sg and negligible concentrations of and S q (H)- In general, octatomic sulfur is the predominant molecular constituent of sulfur vapor at low temperatures, but the equihbrium shifts toward smaller molecular species with increasing temperature and decreasing pressure. 

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