Mass resolution fragmentation

Separation of families by merely increasing the resolution evidently can not be used when the two chemical families have the same molecular formula. This is particularly true for naphthenes and olefins of the formula, C H2 , which also happen to have very similar fragmentation patterns. Resolution of these two molecular types is one of the problems not yet solved by mass spectrometry, despite the efforts of numerous laboratories motivated by the refiner s major interest in being able to make the distinction. Olefins are in fact abundantly present in the products from conversion processes. 

The limitations of SIMS - some inherent in secondary ion formation, some because of the physics of ion beams, and some because of the nature of sputtering - have been mentioned in Sect. 3.1. Sputtering produces predominantly neutral atoms for most of the elements in the periodic table the typical secondary ion yield is between 10 and 10 . This leads to a serious sensitivity limitation when extremely small volumes must be probed, or when high lateral and depth resolution analyses are needed. Another problem arises because the secondary ion yield can vary by many orders of magnitude as a function of surface contamination and matrix composition this hampers quantification. Quantification can also be hampered by interferences from molecules, molecular fragments, and isotopes of other elements with the same mass as the analyte. Very high mass-resolution can reject such interferences but only at the expense of detection sensitivity. 

The helium gas in the trap not only helps in trapping the ions but also cools them (i.e., the kinetic energy of a trapped ion is dissipated through repeated collisions with the He gas), thus forcing the ions to the center of the trap where the quadrupole field is best defined. Both sensitivity and mass resolution are significantly enhanced by the presence of the He gas. Moreover, the same He can also be used to induce fragmentation when working in the MS" mode (see below). 

The sensitivity, compactness, automation, and low prices of ion trap instruments made them very popular in biological MS P Limitations of ion traps include low resolution and mass accuracy at high m/z. In addition, in MS/MS mode, the lower end of the fragment mass range cannot be visualized. Recent developments in the linear geometry of ion traps are aimed at improving on those limitations. 

However, mass spectrometry itself offers two additional degrees of freedom . One can either resolve the complexity of a sample by going to high or even ultra-high mass resolution or one can employ tandem MS techniques to separate the fragmentation pattern of a single component from that of others in a mixture. [2,3] In practice, the coupling of separation techniques to mass spectrometry is often combined with advanced MS techniques to achieve the desired level of accuracy and reliability of analytical information. [1,7,24-27]... 

March, R.E. et al., A fragmentation study of an isoflavone glycoside, genistein-7-O-glucoside, using electrospray quadrupole time-of-flight mass spectrometry at high mass resolution, Int. J. Mass Spectrom., 232, 171, 2004. 

Paul, G., Winnik, W., Hughes, N., Schweingruber, H., Heller, R., and Schoen, A. (2003). Accurate mass measurement at enhanced mass-resolution on a triple quadrupole mass-spectrometer for the identification of a reaction impurity and colfisionally-induced fragment ions of cabergoline. Rapid Commun. Mass Spectrom. 17 561-568. 

Laser desorption Fourier transform mass spectrometry (LD-FTMS) results from a series of peptides and polymers are presented. Successful production of molecular ions of peptides with masses up to 2000 amu is demonstrated. The amount of structurally useful fragmentation diminishes rapidly with increasing mass. Preliminary results of laser photodissociation experiments in an attempt to increase the available structural information are also presented. The synthetic biopolymer poly(phenylalanine) is used as a model for higher molecular weight peptides and produces ions approaching m/z 4000. Current instrument resolution limits are demonstrated utilizing a polyethylene-glycol) polymer, with unit mass resolution obtainable to almost 4000 amu. 

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