Mass spectral

S. E. Stein, D. R. Scott,/. Am. Soc. Mass Spectrom. 1994, 5, 856-866. Optimization and testing of mass spectral library seardi algorithms for compound identification. 

The peak at mje = 98 is taken as the arbitrary standard. The height of the other peaks is measmed relative to it. Once this matrix has been established, ordered sets of mass spectral peak heights at mfe = 69, 83, 84, and 98 constitute the experimental b vector for an unknown mixture that contains or may contain the four... 

Thiazole disulfides absorb at 235 and 258 nm (320-322) and characteristic infrared bands are reported in Ref. 320. The activities of 2-cyclo-hexyldithiomethylthiazoles as vulcanization accelerators have been correlated with their mass-spectral fragmentation patterns (322). 

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. 

In a well-tuned (adjusted) instrument, the shape of a mass spectral peak is approximately triangular (Figure 44.7a), but, in an instrument that is poorly tuned the peak will appear misshapen (Figure 44.7b). Usually, the cause of the skewing of the peak arises from incorrectly adjusted... 

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. 

The National Institutes of Health-EPA mass spectral library is used to identify analyzed components of a sample by comparing their mass spectra with those of authentic specimens held in the library. 

Once the mass spectral information has been acquired, various software programs can be employed to print out a complete or partial spectrum, a raw or normalized spectrum, a total ion current (TIC) chromatogram, a mass chromatogram, accurate mass data, and metastable or MS/MS spectra. 

Thus, a computer attached to a mass spectrometer must operate on two levels. When mass spectral information is arriving, this must be acquired in real time. When the computer has spare time, it controls the operation of the instrument. Both operations are carried out at such a high speed that the dual level of computer tasks is not obvious. 

Lee, T.A., A Beginner s Guide to Mass Spectral Interpretation, Wiley, Chichester, U.K., 1998. 

Pfleger, K., Maurer, H.H., and Weber, A., Mass Spectral and GC Data of Drugs, Poisons, Pesticides, Pollutants and Their Metabolites, VCH, Weinheim, Germany, 1992. 

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

Chiral separations present special problems for vaUdation. Typically, in the absence of spectroscopic confirmation (eg, mass spectral or infrared data), conventional separations are vaUdated by analysing "pure" samples under identical chromatographic conditions. Often, two or more chromatographic stationary phases, which are known to interact with the analyte through different retention mechanisms, are used. If the pure sample and the unknown have identical retention times under each set of conditions, the identity of the unknown is assumed to be the same as the pure sample. However, often the chiral separation that is obtained with one type of column may not be achievable with any other type of chiral stationary phase. In addition, "pure" enantiomers are generally not available. 

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

Monobasic acids are determined by gas chromatographic analysis of the free acids dibasic acids usually are derivatized by one of several methods prior to chromatographing (176,177). Methyl esters are prepared by treatment of the sample with BF.—methanol, H2SO4—methanol, or tetramethylammonium hydroxide. Gas chromatographic analysis of silylation products also has been used extensively. Liquid chromatographic analysis of free acids or of derivatives also has been used (178). More sophisticated hplc methods have been developed recentiy to meet the needs for trace analyses ia the environment, ia biological fluids, and other sources (179,180). Mass spectral identification of both dibasic and monobasic acids usually is done on gas chromatographicaHy resolved derivatives. 

Pentafluorophenylmagnesium bromide or lithium can be converted to other pentafluorophenyl organometabics by reaction with the corresponding metal chloride (237). Bis(pentafluorophenyl)phenylphosphine [5074-71-5] (Ultramark 443), (CgF )2CgH P, is offered commercially as a marker for mass spectral standardi2ation (238). 

FLUOROTRIAZINES Riag-fluoriaated triaziaes are used ia fiber-reactive dyes. Perfluoroalkyl triaziaes are offered commercially as mass spectral markers and have been iatensively evaluated for elastomer and hydraulic fluid appHcations. Physical properties of representative fluorotriaziaes are listed ia Table 13. Toxicity data are available. For cyanuric fluoride, LD g =3.1 ppm for 4 h (iahalatioa, rat) and 160 mg/kg (skin, rabbit) (127). 

Mass spectral fragmentation patterns of alkyl and phenyl hydantoins have been investigated by means of labeling techniques (28—30), and similar studies have also been carried out for thiohydantoins (31,32). In all cases, breakdown of the hydantoin ring occurs by a-ftssion at C-4 with concomitant loss of carbon monoxide and an isocyanate molecule. In the case of aryl derivatives, the ease of formation of Ar—NCO is related to the electronic properties of the aryl ring substituents (33). Mass spectrometry has been used for identification of the phenylthiohydantoin derivatives formed from amino acids during peptide sequence determination by the Edman method (34). 

JICST/JOIS. The Japan Information Center for Science and Technology (fICST) Mass Spectral Database is accessible to users in Japan through the JICST Eactual Database System (fOlS-E). The database uses the NIST/EPA/ MSCD data collection supplemented by spectra from the Mass Spectrometry Society of Japan (84). 

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). 

Mass spectral analysis of quaternary ammonium compounds can be achieved by fast-atom bombardment (fab) ms (189,190). This technique rehes on bombarding a solution of the molecule, usually in glycerol [56-81-5] or y -nitroben2yl alcohol [619-25-0], with argon and detecting the parent cation plus a proton (MH ). A more recent technique has been reported (191), in which information on the stmcture of the quaternary compounds is obtained indirectly through cluster-ion formation detected via Hquid secondary ion mass spectrometry (Isims) experiments. 

Other methods of sensitive detection of radiotracers have been developed more recently. Eourier transform nmr can be used to detect (nuclear spin 1/2), which has an efficiency of detection - 20% greater than that of H. This technique is useful for ascertaining the position and distribution of tritium in the labeled compound (14). Eield-desorption mass spectrometry (fdms) and other mass spectral techniques can be appHed to detection of nanogram quantities of radiolabeled tracers, and are weU suited for determining the specific activity of these compounds (15). 

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. 

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