Ions, mass-to-charge ratios

Crosstalk An unwanted contribution to a LC-MS/MS transition from a previous LC-MS/MS transition. The potential for crosstalk is higher when multiple analytes with identical product ion mass-to-charge ratios are being monitored and when sufficient time is not provided for emptying the collision cell between MRM or SRM transitions. Crosstalk leads to over- or underestimation of an analyte of interest (Tong et al., 1999). 

Source Temperature 350 °C Mass transitions (optimized precursor and product ion mass to charge ratio) in positive ion mode D-24851 390 -> 268 m/z D-24851-D 394 -+272 m/z The instrument parameters have been optimized for the analysis of D-24851 and the internal standard. Total analysis time 5 minutes. 

Ion source APCI, positive mode Mass transitions (optimized precursor and product ion mass to charge ratio) in positive ion mode ... 

After observation of a molecular or pseudomolecular ion, the most important feature of a mass spectrum is the fragmentation behavior, i.e., the differences between the observed ion mass-to-charge ratios and their relative abundances. The rules for structural elucidations for electron ionization (El) are well known and accessible. The reader is referred to McLafferty and Turacek (1993) either as an introduction or as a refresher.30... 

Fig. 6.5—6.9 show CIMS/MS results for these milk fat CLA methyl esters. As is always the case in the CIMS/MS spectra of unsaturated FAME, the [M+54-32] ions are abundant and are easily identified at m z 316 for the 18 2 isomers. The parent, [M+54] ions, are usually completely consumed during coUisional dissociation thus making the [M+54-32] ion useful for easy verification of the parent ion mass to charge ratio in CIMS/MS spectra. The a/co ratios for these milk fat CIA are shown in Table 6.3 and reflect these differences in diagnostic ion abundances. 

Figure 10 A mass spectrum obtained using H3O+, precursor ions following the introduction of laboratory air into the SIFT. Concentrations of the detected species (released from an adjacent laboratory) are given in parts per billion (ppb) in parentheses, u = ion mass-to-charge ratio, c/s = counts per second.

Tg = buffer gas temperature t = reaction u = ion mass-to-charge ratio v = frequency. 

In a mass spectrometer, the molecules, in the gaseous state, are ionized and fragmented. The fragments are detected as a function of their mass-to-charge ratio, m/e. The graphical representation of the ion intensity as a function of m/e makes up the mass spectrogram as illustrated In Figure 3.1. 

Ion chemistry is a product of the 20th century. J J Thomson discovered the electron in 1897 and identified it as a constituent of all matter. Free positive ions (as distinct from ions deduced to exist in solids or electrolytes) were first produced by Thomson just before the turn of the century. He produced beams of light ions, and measured their mass-to-charge ratios, in the early 1900s, culminating in the discovery of two isotopes of neon in 1912 [1]. This year also marked Thomson s discovery of which turns out to be the... 

In odier words, ions with a particular mass-to-charge ratio, m/z, can be selectively passed tlirough the magnetic sector by appropriate choice of a value of V and B (though nonnally V is held constant and only B is varied). 

In GC-MS effluent from the column is introduced directly into the mass spectrometer s ionization chamber in a manner that eliminates the majority of the carrier gas. In the ionization chamber all molecules (remaining carrier gas, solvent, and solutes) are ionized, and the ions are separated by their mass-to-charge ratio. Because each solute undergoes a characteristic fragmentation into smaller ions, its mass spectrum of ion intensity as a function of mass-to-charge ratio provides qualitative information that can be used to identify the solute. 

A plot of ion intensity as a function of the ion s mass-to-charge ratios. 

All mass spectrometers analyze ions for their mass-to-charge ratios (m/z values) by separating the individual m/z values and then recording the numbers (abundance) of ions at each m/z value to give a mass spectrum. Quadrupoles allow ions of different m/z values to pass sequentially e.g., ions at m/z 100, 101, 102 will pass one after the other through the quadrupole assembly so that first m/z 100 is passed, then 101, then 102 (or vice versa), and so on. Therefore, the ion collector (or detector) at the end of the quadrupole assembly needs only to cover one point or focus for a whole spectrum to be scanned over a period of time (Figure 28.1a). This type of point detector records ion arrivals in a time domain, not a spatial one. 

All mass spectrometers analyze ions for their mass-to-charge ratios (m/z values) and simultaneously for the abundances of ions at any given m/z value. By separating the ions according to m/z and measuring the ion abundances, a mass spectrum is obtained. 

Prior separation of mixtures into individual components may not be needed. If the mass spectrometer is capable of MS/MS operation, one of the mass spectrometers is used to isolate individual ions according to m/z value (mass-to-charge ratio), and the other is used to examine their fragmentation products to obtain structural information. 

Another important property of electric and magnetic fields is their ability to separate ions according to their individual masses (m, mj,. .., m ) or, more strictly, their mass-to-charge ratio (mj/z, raji,. mjz). 

A mass spectrometer measures mass-to-charge ratio (m/z) and, often, the charge on the ion is unity, so that m/z = m/1 = m. Thus, a mass spectrometer can be used to measure mass. 

Ion cyclotron resonance analyzer. A device to determine the mass-to-charge ratio (m/z) of an ion in the presence of a magnetic field by measuring its cyclotron frequency. 

Mass spectrograph. An instrument in which beams of ions are separated according to their mass-to-charge ratio (m/z) and in which the deflection and intensity of the beams are recorded directly on a photographic plate or film. 

Resolving power (mass). The ability to distinguish between ions differing slightly in mass-to-charge ratio. It can be characterized by giving the peak width, measured in mass units, expressed as a function of mass, for at least two points on the peak, specifically for 50% and for 5% of the maximum peak height. 

MS", application of successive mass spectrometric measurements n of them), particularly in linked scanning of m/z, which is the ratio of the mass (m) of an ion and the number of charges (z) on it. Older publications used m/e, but as e is the actual charge on an electron and not the number of charges on the ion, the use of m/e was abandoned, m/z. mass-to-charge ratio, a measure of molecular mass PDB. PeeDee Belemnite (a carbon isotope standard see VPDB)... 

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