Mass spectral data

By examining a mass spectrum at sufficiently high resolution, one can obtain the exact composition of each ion in a mass spectrum, unambiguously. Most importantly, determining the accurate mass of [M]+ gives the molecular formula of the compound. 

The relative intensities of the [M]+ , [M+l]+ and [M+2]+ ions exhibit a characteristic pattern depending on the elements that make up the ion. For any molecular ion (or fragment) which contains one bromine atom, the mass spectrum will contain two 

Any molecular ion (or fragment) which contains 2 bromine atoms will have a pattern of M M+2 M+4 with signals in the ration 1 3 1 and any molecular ion (or fragment) which contains 2 chlorine atoms will have a pattern of M M+2 M+4 with signals in the ration 10 6 1. 

Electronic databases of the mass spectral fragmentation patterns of known molecules can be rapidly searched by computer. The pattern and intensity of fragments in the mass spectrum is characteristic of an individual compound so comparison of the experimental mass spectrum of a compound with those in a library can be used to positively identify it, if its spectrum has been recorded previously. 

It is now common to couple an instrument for separating a mixture of organic compounds e.g. using gas chromatography (GC) or high performance liquid chromatography (HPLC), directly to the input of a mass spectrometer. In this way, as each individual compound is separated from the mixture, its mass spectrum can be recorded and compared automatically with the library of known compounds and identified immediately if it is a known compound. 

The relative atomic mass of an element is the weighted mean of the isotopic masses. The weighted mean is calculated from the masses of all the possible isotopes of the element, taking into account the natural relative abundance of each isotope. 

The intensity of the isotopic peaks is related to the abundance of the isotope present and to the total number of atoms present in that molecule, i.e. it is related to the probability of finding that isotope in the molecule the greater the abundance and the more atoms there are present, the greater the chance of finding an isotope and the more intense the isotopic peak. 

For instance, carbon has two naturally occurring isotopes, with a natural abundance of 99.89% and C with a natural abundance of 1.11%, so that roughly one in every 100 carbon atoms will be a C. In a molecule containing 10 carbon atoms there are 10 chances of finding a atom, which adds up to a 1 in 10 chance that this particular molecule will contain one C, so that for a Cjo molecule we should see a peak corresponding to M + 1 with an intensity of 1/10 of that of the molecular ion. For small to medium sized molecules i.e. 100 carbons) the most abundant peak is the one corresponding to exclusively C atoms  

Before we can discuss the issue of mass accuracy we must first consider what we mean by this term. If we examine Table 5.1 more closely, we see that the only element listed with an integral mass i.e. a whole number) is as defined by the lUPAC convention, and when we calculate the monoisotopic mass of an analyte we always find that it is not an integer. 

However, when we calculate the accurate masses of these com- 

Apart from the actual acquisition of the mass spectrum and its subsequent display or printout, the raw mass spectral data can be processed in other ways, many of which have been touched on in other chapters in thi.s book. Some of the more important aspects of this sort of data manipulation are explained in greater detail below. 

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Mass spectra are reproduced with permis Sion from EPA/NIH Mass Spectral Data Base Supplement I S R Heller and G W A l lne National Bureau of Stan dards 1980... 

A very good general survey for interpreting mass spectral data is given by R. M. Silverstein, G. C. Bassler, and T. C. Morrill, Spectrometric Identification of Organic Compounds, 4th ed., Wiley, New York, 1981. 

Table 7.76 is condensed, with permission, from the Catalog of Mass Spectral Data of the American Petroleum Institute Research Project 44. These, and other tables, should be consulted for further and more detailed information. 

Stauffer, D.B. and McLafferty, F.W., The Wiley/NBS Registry of Mass Spectral Data, Wiley Interscience, New York, 1989. 

EPA.INIH Mass Spectral Data Base, Vol. 1, U.S. National Bureau of Standards, Wasliiagton, D.C., 1978, p. 5. 

Treatment of halomycin B (55) using nitrous acid yields rifamycin S (24) and the pyrroHdine (57) as shown in Figure 6. The halomycin B stmcture was confirmed by heating rifamycin O (23) and (57) in tetrahydrofiiran to yield halomycin B (20) which can also be converted to rifamycin S by electrochemical oxidation (213). Upon treatment with nitrous acid, halomycin A (54) yields rifamycin S along with the pyrroHdine (58). The stmcture for halomycin C (56) was deterrnined to be 20-hydroxy halomycin B based on mass spectral data (212). 

The melting points, optical rotations, and uv spectral data for selected prostanoids are provided in Table 1. Additional physical properties for the primary PGs have been summarized in the Hterature and the physical methods have been reviewed (47). The molecular conformations of PGE2 and PGA have been determined in the soHd state by x-ray diffraction, and special H and nuclear magnetic resonance (nmr) spectral studies of several PGs have been reported (11,48—53). Mass spectral data have also been compiled (54) (see Mass spectrometry Spectroscopy). 

W. Jennings and T. ShS o2im.o. o, Qualitative Analysis of Flavor andFragrance Volatiles by Glass Capillay Gas Chromatography, Academic Press, Inc., New York, 1980 also iacludes retention iadexes and mass spectral data. 

Static SIMS has been demonstrated to be a valuable tool in the chemical characterization of surfaces. It is unique in its ability to provide chemical information with high surface sensitivity. The technique is capable of providing mass spectral data (both positive and negative spectrometry), as well as chemical mapping, thereby giving a complete microchemical analysis. The type of information provided by... 

A number of azacrown compounds were reported by Lockhart and coworkers in 1973. In a typical case, 2-aminophenol was heated at reflux with an equivalent of tet-raethylene dichloride for 48 h. A mixture of the monoaza-15-crown-5 (5) and the mono-aza-12-crown-4 (4) shown in Eq. (4.4) were obtained. Structural assignments were based on H-NMR, IR and mass spectral data. 

Mass spectra are reproduced with permission from EPA/NIH Mass Spectral Data Base, Supplement I, S. R. Heller and G. W. A. Milne, National Bureau of Standards, 1980. 

Propose structures for compounds that fit the following mass-spectral data ... 

Registiy of Mass Spectral Data, 412 Replication (DNA). 1106-1107 direction of, 1107 error rate during. 1107 lagging strand in, 1107 leading strand in, 1107 Okazaki fragments in, 1107 replication fork in, 1107 Replication fork (DNA), 1107 Reserpine, structure of, 65 Residue (protein), 1027 Resist, photolithography and, 505-506... 

Mass spectral data on l-(arylsulfonyl)-l//-azepines have been amassed,73 and the fragmentation patterns of several 1-acyl-1//-azepines elucidated.61 For the latter systems, the base peaks correspond to the azatropylium cation (m/z 92). Loss of hydrogen cyanide to yield the cyclo-pentadienyl cation (m/z 65) has also been noted. 

Structure ofF Although F has never been obtained in a completely pure state, the FAB mass spectral data of F [m/z 687 (M + Na)+ and 665 (M+H)+], and the comparison of the H and 13C NMR spectra of F with those of Oxy-F, suggested structure 6 for this compound. To confirm this structure, F was subjected to ozonolysis, followed by diazomethane treatment. The expected diester 5 was successfully isolated, indicating that 6 is indeed the structure of compound F (Nakamura et al., 1988). The structure of the luminescence reaction product of F is considered to be 8 on the basis of comparison with the dinoflagellate luminescence system (see Chapter 8). 

Calculations. The atoms of incorporated lsO is calculated from mass spectral data. When the ratio of the peak heights at mass-to-charge ratio (m/e) 44, 46 and 48 for CO2 is X-.Y-.Z, assuming that the height of each peak is strictly proportional to the number of CO2 molecules, the atom fraction of l80 in CO2, C, is given by ... 

List possible structures or partial structures consistent with the mass spectral data. If probable molecular formulae are tabulated and the structure is still unknown, possible structures can easily be obtained from such sources as Beilstein, Merck Index, Handbook of Chemistry, Handbook of Chemistry... 

McLafferty. F. W., and Stauffer, D. B. Important Peak Index of the Registry of Mass Spectral Data. New York Wiley-Interscience, 1991. 

Compilations of Reference Spectra There are several compilations of reference mass spectra available of which the oldest is the American Petroleum Institute (Ref 82) collection of spectra obtained mostiy on the older type instruments. Recent collections index spectra variously, eg, under reference number (Ref 19). molecular weight (Refs 12 19), molecular formula (Ref 19), fragment ion values (Ref 19), and base peak (Refs 12 19). A quarterly journal, Archives of Mass Spectral Data ... 

Mass Spectral Data , ASTM Special Technical Publication No 356, Phila, Pa (1963) 12a) J.H. 

Cornu R. Massot, Compilation of Mass Spectral Data , Heyden Son, London (1966)... 

T. Cairns, E. G. Siegmund and R. A. Jacobson, Mass Spectral Data Compilation of Pesticides and Industrial Chemicals, Food and Drug Administration, Los Angeles, 1981. 

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