Steven H. Hoke

Occurrence and fragmentation of high-mass fullerenes

Abstract Extracts of graphitic soot are shown by electron attachment mass spectrometry to contain, in addition to the well-known fullerenes C 60 and C 70 , smaller quantities of larger carbon clusters, up to C 200 . A structure for one of the more abundant clusters, C 76 , is proposed. The data show the conspicuous absence of particular clusters. The relative stabilities of C 60 , C 70 and C 84 were investigated by charge exchange and collision activated dissociation experiments. All the fullerene ions showed remarkable stability to fragmentation. At the highest collision energies accessible, fragmentation of C 2+ 70 and C − 70 produced a series of products from C 2 loss, including the conspicuous formation of C 60 ions.

Mass spectrometers: instrumentation

Abstract Developments in mass spectrometry instrumentation over the past three years are reviewed. The subject is characterized by an enormous diversity of designs, a high degree of competition between different laboratories working with either different or similar techniques and by extremely rapid progress in improving analytical performance. Instruments can be grouped into genealogical charts based on their physical and conceptual interrelationships. This is illustrated using mass analyzers of different types. The time course of development of particular instrumental concepts is illustrated in terms of the s-curves typical of cell growth. Examples are given of instruments which are at the exponential, linear and mature growth stages. The prime examples used are respectively: (i) hybrid instruments designed to study reactive collisions of ions with surfaces: (ii) the Paul ion trap; and (iii) the triple quadrupole mass spectrometer. In the area of ion/surface collisions, reactive collisions such as hydrogen radical abstraction from the surface by the impinging ion are studied. They are shown to depend upon the chemical nature of the surface through the use of experiments which utilize self-assembled monolayers as surfaces. The internal energy deposited during surface-induced dissociation upon collision with different surfaces in a BEEQ instrument is also discussed. Attention is also given to a second area of emerging instrumentation, namely technology which allows mass spectrometers to be used for on-line monitoring of fluid streams. A summary of recent improvements in the performance of the rapidly developing quadrupole ion trap instrument illustrates this stage of instrument development. Improvements in resolution and mass range and their application to the characterization of biomolecules are described. The interaction of theory with experiment is illustrated through the role of simulations of ion motion in the ion trap. It is emphasized that mature instruments play a dominant role in most work using mass spectrometers. This is illustrated with recent results on the chemistry of C+.60 including the formation of covalent adducts with aromatic compounds. Quantitative analysis of methylated nucleosides and structural studies of the anti-cancer drug taxol are also discussed. A compendium of mass spectrometers constructed over the past three years is provided. This includes a variety of hybrid instruments, combinations of sector mass spectrometers with traps, instruments designed to study collision dynamics, and many more.

Evaluation of different data-processing options for a flow system with a well-stirred mixing chamber

Abstract This paper describes the evaluation of several data-processing options for a flow-based sample processor with a well-stirred mixing chamber. Data-processing options evaluated include peak-height, peak-area and time-interval methods with different choices of reference points. Results are compared with theoretical expectations and effects of experimenal parameters on the different methods are compared by using relative error coefficients. It is found that theoretical equations based on a kinetic model for the system describe shapes of calibration equations very well and predict slopes of calibration plots to within a few percent of experimental values. These results show that other less rigorous treatments can lead to conclusions that are valid only for selected sets of circumstances.

Chemical modification of deoxyribonucleic acids: Quantitation of 3-methylthymidine and O4-methylthymidine by tandem mass spectrometry

Abstract Quantitation of 3-methylthymidine and O4-methylthymidine generated in the reaction of calf thymus DNA with methyl methanesulfonate (MeMS) and 1-methyl-1nitrosourea (MeNU) by mass spectrometry is reported. Quantitative precision of 7% or better is achieved on samples of 10−12 −10−13 mole in the HPLC and a final stage of separation before quantification by tandem mass spectrometry using desorption chemical ionization. Synthetic CD3-labeled nucleosides were used as internal standards for mass spectral quantification. A unique mass spectrometric scanning procedure, which allowed simultaneous MS—MS product ion analysis of both the analyte and the internal standard, was utilized to enchance precision and accuracy in these low level determinations. MeNU (a potent carcinogen) resulted in 18&%; 3-methylation and 0.17% O4-methylation of deoxythymidine whereas MeMS (a weak carcinogen) produced only 6.8% 3-methylation and 0.005% of deoxythymidine. These results demonstrate that the sensitivity and accuracy of this method should be adequate for the detection and quantification of methyl-nucleosides at the sub-picomole level at which mutation is induced in cell cultures.

Ion/molecule reactions leading to WFn+ (n = 1−5): implications for the mechanisms of ion/surface reactions

Abstract Reactions between W(CO)6 and perfluorohexane (C6F14) in a chemical ionization source yield the complex ion [W(CO)6.C6F13]+. When this ion is selected in an MS-MS experiment and dissociated using 195eV collisions upon argon, products WFn+ (n = 1−5) are generated. By simultaneously mass-selecting all the isotopic forms of the parent ion, the tungsten-containing fragment ions WFn+ (n = 1−5) are easily identified through their characteristic isotopic pattern in the product ion spectrum. These collisional activation data suggest that WFn+ (n = 1−5) can be formed in a single collision of W(CO)6+ with a fluorocarbon molecule; this process may be operative in collisions of tngsten-containing ions with fluorinated self-assembled monolayer surfaces.

Pyrolytic and gas phase fullerene derivatization reactions

Abstract The bulk production of naphthyne derivatives of [60]fullerene, C 60 , is achieved by pyrolysis of 1,8-diiodonaphthalene in the presence of C 60 . Desorption chemical ionization mass spectra, recorded in the negative ion mode, show the addition of up to ten naphthyne units to a single C 60 molecule. Products containing two C 60 molecules are also generated. Tandem mass spectrometry confirms that covalent bonding has occurred. Similar reactions are described for the reactive intermediates generated from 1,8-naphthalic anhydride, 9-iodoanthracene, 2,6-dimethoxyiodobenzene, 2-iodonaphthalene and hexabromobenzene. Evidence for a [4 + 2] Diels—Alder ion/molecule reaction between mass-selected fullerene cations and methoxy-substituted 1,3-butadienes is presented. Ion/molecule reactions of various closed shell cations derived from the dissociative electron ionization of chlorine containing compounds are shown to result in the methylation, acylation, phenylation and benzylation of fullerenes in the course of positive ion chemical ionization. In the negative ion mode, halogenated fullerene anions are observed. At high desorption temperatures, the addition of at least 30 hydrogen atoms to C 60 is reported.

Taxol and taxane formation in plant cell culture

The production of taxol, cephalomannine and baccatin III from a suspension cell culture of Taxus brevifolia has been investigated using HPLC and tandem mass spectrometry (MS/MS). Interference from other products in the cell culture medium led to development of an MS/MS assay based on negative ion desorption chemical ionization using [2H3]-labelled internal standards for measurements of these compounds at the level of 2–8 ng cm–3 of medium. The use of parent scans allowed the detection of a number of new taxanes for further study.