Mass spectrometric analyses

These equations indicate that the energy of the scattered ions is sensitive to the mass of the scattering atom s in the surface. By scanning the energy of the scattered ions, one obtains a kind of mass spectrometric analysis of the surface composition. Figure VIII-12 shows an example of such a spectrum. Neutral, that is, molecular, as well as ion beams may be used, although for the former a velocity selector is now needed to define ,. ... 

It is interesting to note that recent evidence shows that even extra-terrestrially formed hydrocarbons can reach the Earth. The Earth continues to receive some 40,000 tons of interplanetary dust every year. Mass-spectrometric analysis has revealed the presence of hydrocarbons attached to these dust particles, including polycyclic aromatics such as phenanthrene, chrysene, pyrene, benzopyrene, and pentacene of extraterrestrial origin indicated by anomalous isotopic ratios. 

Laser desorption to produce ions for mass spectrometric analysis is discussed in Chapter 2. As heating devices, lasers are convenient when much energy is needed in a very small space. A typical laser power is 10 ° W/cm. When applied to a solid, the power of a typical laser beam — a few tens of micrometers in diameter — can lead to very strong localized heating that is sufficient to vaporize the solid (ablation). Some of the factors controlling heating with lasers and laser ablation are covered in Figure 17.2. 

To achieve sufficient vapor pressure for El and Cl, a nonvolatile liquid will have to be heated strongly, but this heating may lead to its thermal degradation. If thermal instability is a problem, then inlet/ionization systems need to be considered, since these do not require prevolatilization of the sample before mass spectrometric analysis. This problem has led to the development of inlet/ionization systems that can operate at atmospheric pressure and ambient temperatures. Successive developments have led to the introduction of techniques such as fast-atom bombardment (FAB), fast-ion bombardment (FIB), dynamic FAB, thermospray, plasmaspray, electrospray, and APCI. Only the last two techniques are in common use. Further aspects of liquids in their role as solvents for samples are considered below. 

For mass spectrometric analysis of an analyte solution using a plasma torch, it is necessary to break down the solution into a fine droplet form that can be swept into the flame by a stream of argon gas. On the way to the flame, the droplets become even smaller and can eventually lose all solvent to leave dry analyte particulate matter. This fine residual matter can be fragmented and ionized in the plasma flame without disturbing its operation. 

Dynamic headspace GC/MS. The distillation of volatile and semivolatile compounds into a continuously flowing stream of carrier gas and into a device for trapping sample components. Contents of the trap are then introduced onto a gas chromatographic column. This is followed by mass spectrometric analysis of compounds eluting from the gas chromatograph. 

Stable ion. An ion that is not sufficiently excited to dissociate into a daughter ion and associated neutral fragments, or to react further in the time frame of the mass spectrometric analysis under stated experimental conditions. 

Sputtered Neutral Mass Spectrometry (SNMS) is the mass spectrometric analysis of sputtered atoms ejected from a solid surface by energetic ion bombardment. The sputtered atoms are ionized for mass spectrometric analysis by a mechanism separate from the sputtering atomization. As such, SNMS is complementary to Secondary Ion Mass Spectrometry (SIMS), which is the mass spectrometric analysis of sputtered ions, as distinct from sputtered atoms. The forte of SNMS analysis, compared to SIMS, is the accurate measurement of concentration depth profiles through chemically complex thin-film structures, including interfaces, with excellent depth resolution and to trace concentration levels. Genetically both SALI and GDMS are specific examples of SNMS. In this article we concentrate on post ionization only by electron impact. 

Figura 1 Schematic of SNMS analysis. Neutral atoms and molecules sputtered from the sample surface by energetic ion bombardment are subsequently ionized for mass spectrometric analysis.

It is very evident in Figure 3 that the chemical complexity of Hasteloy presents special problems for mass spectrometric analysis using a quadrupole mass spectrometer with low mass resolution. Molecular ions comprised of combinations of matrix and plasma atoms are formed in abundance and will obscure many elements... 

Somewhat later, Travis and Busch reported that extraction of the residue from Eq. (6.8) with hot ethanol afforded the dimer of 10 in 25% yield . The latter, 1,4,8,11, 15,18,22,25-octathiooctacosane, was characterized by mass spectrometric analysis as well as the customary analytical methods. It was found that by dilution of reactants prior to mixing, the yield of [monomer] is greatly increased (50—60%) while the yield of [dimer] is lowered substantially . One might have expected the larger rather than the smaller ring to be more favored at higher dilution, but there is no further comment on this point. 

Under certain conditions surface catalytic deuterations can lead to the exchange of benzylic hydrogens. An example in the steroid field is the exchange of the benzylic hydrogens in estrone methyl ether (42) with deuterium in the presence of palladized charcoal." " According to mass spectrometric analysis, the product (43) contains three deuteriums (83 %), which have been assigned to the 6- and 9a-positions on the basis of NMR evidence." " ... 

ATPase inhibitor. In such patients, inhibition of the sodium pump in the cells lining the blood vessel wall results in accumulation of sodium and calcium in these cells and the narrowing of the vessels to create hypertension. An 8-year study aimed at the isolation and identification of the agent responsible for these effects by researchers at the University of Maryland Medical School and the Upjohn Laboratories in Michigan recently yielded a surprising result. Mass spectrometric analysis of compounds isolated from many hundreds of gallons of blood plasma has revealed that the hypertensive agent is ouabain itself or a closely related molecule ... 

Laser vaporization of a composite pressed disc of graphite and BN using He as carrier gas, followed by mass spectrometric analysis, gave a range of clusters with even numbers of atoms from less than 50 to well above the peak... 

Ahearn, Mass Spectrometric Analysis of Solids, Elsevier, NY (1966) 23) M.S.B. Munson ... 

Qualitative or quantitative mass spectrometric analysis can be made by one of two alternative configurations. Either the sample is decomposed in the high vacuum chamber of the mass spectrometer (MS) itself or reaction proceeds in an external system at higher pressure (e.g. a microbalance)... 

Co(en)3]X3 complexes [1113,1130] decompose in nitrogen to yield CoX2 and give Co304 in air, the sequence of stability with variation in X is SCN < Cl < I" = Br" < S04 < NOJ. Mass spectrometric analysis of the products of reaction in vacuum indicated the formation of large quantities of NH3 and no ethylenediamine. Decomposition does not, therefore, involve stepwise release of the ligand. 

A number of analytical techniques such as FTIR spectroscopy,65-66 13C NMR,67,68 solid-state 13 C NMR,69 GPC or size exclusion chromatography (SEC),67-72 HPLC,73 mass spectrometric analysis,74 differential scanning calorimetry (DSC),67 75 76 and dynamic mechanical analysis (DMA)77 78 have been utilized to characterize resole syntheses and crosslinking reactions. Packed-column supercritical fluid chromatography with a negative-ion atmospheric pressure chemical ionization mass spectrometric detector has also been used to separate and characterize resoles resins.79 This section provides some examples of how these techniques are used in practical applications. 

The following very important observations must be accounted for in any mechanistic proposal cells were incubated with a mixture of (2 -l3C)AIRs and (3-,5N)AIRs. A mass-spectrometric analysis of the product of biosynthesis showed that this was a mixture of two pyrimidines, one labeled at the methyl carbon atom, the other at N-l no pyrimidine twice labeled or unlabeled was observed these latter would have arisen from recombination of fragments carrying C-2 or N-3. The conclusion is that the fragments containing C-2 and N-3, orig-... 

Craig, H. (1957a). Isotopic standards for carbon and correction factors for mass-spectrometric analysis of carbon dioxide. Geochim. Cosmochim. Acta 12, 133-149. 

Figure 5.59 Molecular structures of the diarrhetic shellfish poisons (a) pectenotoxin-6 (PTX6) (b) okadaic acid (OA) (c) dinophysistoxin-1 (DTXl) (d) yessotoxin (YTX). Reprinted from J. Chromatogr., A, 943, Matrix effect and correction by standard addition in quantitative liquid chromatographic-mass spectrometric analysis of diarrhetic shellfish poisoning toxins , Ito, S. and Tsukada, K., 39-46, Copyright (2002), with permission from Elsevier Science.

Table I. Mass Spectrometric Analysis of Decomposition Residues...

C22-0026. Mass spectrometric analysis of charcoal from an archaeological dig gave a carbon-14... 

He, X.G. et al, Liquid chromatography-electrospray mass spectrometric analysis of curcuminoids and sesquiterpenoids in turmeric Curcuma longa), J. Chromatogr. A, 818, 127, 1998. 

ESI-MS has emerged as a powerful technique for the characterization of biomolecules, and is the most versatile ionization technique in existence today. This highly sensitive and soft ionization technique allows mass spectrometric analysis of thermolabile, non-volatile, and polar compounds and produces intact ions from large and complex species in solution. In addition, it has the ability to introduce liquid samples to a mass detector with minimum manipulation. Volatile acids (such as formic acid and acetic acid) are often added to the mobile phase as well to protonate anthocyanins. A chromatogram with only the base peak for every mass spectrum provides more readily interpretable data because of fewer interference peaks. Cleaner mass spectra are achieved if anthocyanins are isolated from other phenolics by the use of C18 solid phase purification. - ... 

Herbach, K.M. et al.. Isotope ratio mass spectrometrical analysis of betanin and isobetanin isolates for authenticity evaluation of purple pitaya-based products. Food Chem., 99, 204, 2006. 

The analyte must be converted into a volatile compound suitable for mass-spectrometric analysis. Procedures for C, N, and O follow those developed for conventional organic microanalysis— oxidation of organic C to COj, reduction of organic N to N2, and conversion of O2 into CO or COj. In most procedures, cryogenic purification of the products is carried out before mass spectrometry, and both off-line and on-line procedures have been developed. 

Figure4.72 Mass spectrometric analysis of product formation of dimethoxylation of methyl 2-furoate for various flow rates.

The analysis of the neutral gas composition in a discharge yields useful information on the mechanisms and kinetics of silane dissociation. However, it should be borne in mind that with mass-spectrometric analysis one only detects the final products of a possibly long chain of reactions. 

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