Mass/charge accurate determination

In tandem MS mode, because the product ions are recorded with the same TOF mass analyzers as in full scan mode, the same high resolution and mass accuracy is obtained. Isolation of the precursor ion can be performed either at unit mass resolution or at 2-3 m/z units for multiply charged ions. Accurate mass measurements of the elemental composition of product ions greatly facilitate spectra interpretation and the main applications are peptide analysis and metabolite identification using electrospray iomzation [68]. In TOF mass analyzers accurate mass determination can be affected by various parameters such as (i) ion intensities, (ii) room temperature or (iii) detector dead time. Interestingly, the mass spectrum can be recalibrated post-acquisition using the mass of a known ion (lock mass). The lock mass can be a cluster ion in full scan mode or the residual precursor ion in the product ion mode. For LC-MS analysis a dual spray (LockSpray) source has been described, which allows the continuous introduction of a reference analyte into the mass spectrometer for improved accurate mass measurements [69]. The versatile precursor ion scan, another specific feature of the triple quadrupole, is maintained in the QqTOF instrument. However, in pre-... 

Salt concentrations were obtained by the addition of known weights of dried salt to the solvent mixture. The compositions of the condensed equilibrium vapor samples and the previously prepared ethanol-water charges to the still were determined as previously outlined. The mole fractions of the salt, ethanol, and water charged to the Othmer still were thus accurately determined by mass balance calculations. 

Coupling mass spectrometry (MS) to capillary electrophoresis provides detection and identihcation of amino acids, peptides, and proteins based on the accurate determination of their molecular masses [15]. The most critical part of coupling MS to CE is the interface technique employed to transfer the sample components from the CE capillary column into the vacuum of the MS. Electrospray ionization (ESI) is the dominant interface which allows a direct coupling under atmospheric pressure conditions. Another distinguishing features of this soft ionization technique when applied to the analysis of peptides and proteins is the generation of a series of multiple charged, intact ions. 

Mass spectrometry A rapid and sensitive technique for separating and determining the structure of molecules by very accurate measurement of their mass/charge ratio. 

There are mainly two methods for chemical composition analysis hydrolysis method and MS method. Hydrolysis method is by adding ot-Cal to induce hydrolysis reaction and after the reaction is analyzed by HPLC MS is the direct detection of the product composition mass/charge ratio and can more accurately determine the composition of the product chemical components. 

In this study, the molecular mass and net charge of MUPs from six wild mice, taken from two separate populations, have been determined by electrospray ionization mass spectrometry and anion exchange chromatography respectively. This method of analysis uniquely identifies individual MUPs and has allowed an accurate determination of the number of different MUPs produced by these animals. In this limited sample, the number is much greater than previously observed in inbred mice. The results are discussed both in terms of the total number of MUPs characterised and the variation in heterogeneity between individual animals and populations. 

Besides suppression of sensitivity caused by solutions with high ionic strength [11,12], high salt concentrations also affected the accuracy of isotope ratio determinations, possibly due to greater losses of the lower-mass uranium isotopes as a result of ion-ion repulsions in the ion beam known as the space-charge effect. While this may not be much of an issue for water analyses, the application of these principles to the accurate determination of uranium isotope ratios in urine imphes that either one needs to attempt a close matrix match for every sample or sample preparation should include the elimination of as many neutral and ionic compounds as possible within the constraints of minimal sample preparation complexity. 

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