Mass-to-charge ratio of ions

The heart of the mass spectrometer is the mass analyzer, the function of which is to measure the mass-to-charge ratios of ions and provide a means of their identification. This is achieved by a combination of a dispersive action to separate the ions according to their m/e ratios and a focusing action to maximize the resolved ion intensities... 

A second commonly used mass analyzer is the quadrupole. A quadrupole acts as a mass filter, allowing a certain mass-to-charge ratio of ions to be transmitted while filtering out all others. The quadrupole consists of a set of four electrodes positioned in an array. Superimposed radio frequency and direct current electric fields can be mutually tuned to allow transmission of ions of the selected mass-to-... 

Unfortunately, the number of compounds that can be searched for specific Infrared bands, mass-to-charge ratios of Ions, gas... 

The molecular ion for compounds containing only C, H, and O always has an even mass-to-charge value. Why What can you say about the mass-to-charge ratio of ions that arise from fragmentation of one bond in the molecular ion from fragmentation of two bonds in the molecular ion ... 

Mass spectrometry (MS) is the study of ions created as a result of ionization/ fragmentation as determined electrically in the gas phase (neutral molecules are not observed) [1]. The mass spectrum is a graphical representation of the ion abundance versus the mass-to-charge ratio mli where m is the mass and z is the charge) of the ions separated in a mass spectrometer. The most important peak for identification of a molecule is the molecular ion (M+ ) or quasimolecular ion (e.g. MNa" ") as this peak has the same mass as the molecule. The mass spectrometer actually measures the mass-to-charge ratio of ions therefore, the molecular ion with a single charge is detected at a value that represents the mass of the molecule. 

Tandem mass spectrometry (MS/MS) is a method for obtaining sequence and structural information by measurement of the mass-to-charge ratios of ionized molecules before and after dissociation reactions within a mass spectrometer which consists essentially of two mass spectrometers in tandem. In the first step, precursor ions are selected for further fragmentation by energy impact and interaction with a collision gas. The generated product ions can be analyzed by a second scan step. MS/MS measurements of peptides can be performed using electrospray or matrix-assisted laser desorption/ionization in combination with triple quadruple, ion trap, quadrupole-TOF (time-of-flight), TOF-TOF or ion cyclotron resonance MS. Tandem... 

The quantity mle is the conventional notation for the mass-to-charge ratio of the molecular ions, with the mass a multiple of the atomic mass constant tnu and the charge a multiple of the fundamental charge e. 

In contrast to most other ionization methods, the majority of ions produced by electrospray are multiply charged. This is of great significance as the mass spectrometer measures the m/z (mass-to-charge) ratio of an ion and the mass range of an instrument may therefore be effectively extended by a factor equivalent to the number of charges residing on the analyte molecule, i.e. an ion of m/z 1000 with... 

The LC/MS/MS method utilizes the principle of three-dimensional separation to achieve excellent selectivity based on chromatographic separation (reversed-phase, size-exclusive, ionic, etc.), the unique mass-to-charge ratio of the analyte s parent ion, and the fragment ion. A sample clean up... 

Capillary electrophoresis (CE) either coupled to MS or to laser-induced fluorescence (LIF) is less often used in metabolomics approaches. This method is faster than the others and needs a smaller sample size, thereby making it especially interesting for single cell analysis [215] The most sensitive mass spectrometers are the Orbitrap and Fourier transform ion cyclotron resonance (FT-ICR) MS [213]. These machines determine the mass-to-charge ratio of a metabolite so accurate that its empirical formula can be predicted, making them the techniques of choice for the identification of unknown peaks. 

Fig. 3.7. Dyes used in these experiments and the mass-to-charge ratio of the major ion from each that was observed or monitored. Reprinted with permission from G. J. Van Berkel el al. [88].

Mass spectrometers use the difference in mass-to-charge ratio (m/z) of ionized atoms, molecular fragments, or whole molecules to differentiate between them. Mass spectrometry is therefore useful for quantitation of atoms or molecules and also for determining chemical and structural information about them [329, 531-533]. Molecules have distinctive fragmentation patterns which provide information to identify structural components. The general operation of a mass spectrometer is to (1) create gas-phase ions, (2) separate the ions in space or time based on their mass-to-charge ratio, and (3) measure the quantity of ions of each mass-to-charge ratio. The ion separation power of a mass spectrometer is described by the resolution, which is defined as ... 

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