bluuebunny/crossref_metadata_2025 huggingface dataset:
Bimolecular reactions involving the radical site of the distonic ion ·CH2CH2CH2CO+
Authors: Stirk Krista M. , Smith Rebecca L. , Orlowski Joe C. , Kenttämaa Hilkka I.
Published: May 2005

A systematic comparison of the reactivity of the γ‐dictonic ion ·CH2CH2CH2CO+ to that of its even‐electron analog, CH3CH2CH2CO+, and a related conventional radical cation, ionized cyclopentanone, was carried out using a dual‐cell Fourier‐transform ion cyclotron resonance mass spectrometer. Each of the ions exhibits unique chemical reactivity. The conventional radical cation reacts with neutral reagents primarily by electron transfer. The even‐electron acylium ion CH3CH2CH2CO+ is unreactive towards most of the neutral molecules studied; slow proton transfer is the only reaction observed with a few reagents. In sharp contrast to the behavior of these two ions, the distonic ion undergoes a variety of reactions with each neutral reagent. Most of these reactions involve a homolytic bond cleavage in the neutral reagent, leading to abstraction of an atom or a radical by the ion. Although reactions directly involving the charge site are not common for this ion, many of its reactions are likely to be catalyzed by the charge site. Initial bond formation at the charge site stabilizes the collision complex, extending its lifetime. This binding may also favorably position the neutral molecule for a subsequent reaction with the radical site of the ion. Accordingly, relatively facile radical abstraction reactions were observed for those reagents which react through a favorable six‐membered transition state after bonding to the charge site. These neutral reagents react similarly, but at a slower rate, with the lower homolog, ·CH2CH2CO+, presumably because a six‐membered transition state is not accessible in this case.
Plasma desorption mass spectrometry of anthocyanidins
Authors: Wood Karl V. , Bonham Connie C. , Ng Jocelyn , Hipskind John , Nicholson Ralph
Published: May 2005

Plasma desorption mass Spectrometry (PDMS), developed for the mass analysis of biopolymers, has found application in the analysis of anthocyanidins, an important class of color‐producing compounds in plants. Anthocyanidins, which have hitherto proven extremely difficult to analyze by any type of mass spectrometric technique, can be analyzed routinely to nanogram levels using PDMS. A simple extraction/hydrolysis scheme can be used to screen for these compounds.
Mass spectrometric investigation of the evaporation properties of Ba2CaWO6 and Ba2SrWO6
Authors: Popovič Arkadij , Bencze Laszlo , Marsel Jože , Lesar Antonija , Vass‐Balthazar K. , Kaposi O.
Published: May 2005

The vaporization of Ba2CaWO6 and Ba2SrWO6 was investigated by Knudsen‐cell mass spectrometry. According to the results obtained with a Knudsen cell made of tungsten, the reduction of barium‐calcium tungstates is a non‐equilibrium process magnified image whereas the sublimation of BaWO4 and its decomposition in the gas phase to BaO(g) and WO3(g) are equilibrium reactions. From the temperature dependence of the partial pressure BaWO4(g)
magnified image
the enthalpy of sublimation is obtained as ΔH = 469 ± 4kJ/mol, which is in excellent agreement with the value obtained by third‐law calculations. The origin of the most abundant ions in the gas phase, i.e., BaWO, BaWO, BaO+ Ba+ etc, has been explained from measurements of the corresponding ionization energy (IE) and appearance energy (AE) values.

The difference between the AE values for Ba2CaWO6 and Ba2SrWO6 is negligible. The presence of BaWO4 in the condensed phase was confirmed by X‐ray diffraction measurements. Neither X‐ray analysis nor the mass spectra show the presence of CaWO4 or SrWO4 in the solid phase or in the gas phase.
Gas chromatography/mass spectrometric analysis of urinary nucleosides in cancer patients; potential of modified nucleosides as tumour markers
Authors: Langridge James I. , McClure Tom D. , Ei‐Shakawi Salah , Fielding Andrew , Schram Karl H. , Newton Russell P.
Published: May 2005

Analysis of urine from cancer patients by capillary gas chromatography/mass spectrometry positively identified 14 urinary nucleosides including several modified nucleosides. Levels of the modified nucleosides 1‐methyl‐adenosine, 2‐methylguanosine, N2,N2‐dimethylguanosine and 1‐methylinosine as well as the total nucleoside level were elevated in the urine when a malignant tumour was present; the levels of N2,N2‐dimethylguanosine were found to correlate with the stage of the cancer.
Collisional ion activation in the ion trap by a three‐step tickle function
Authors: Paradisi Cristina , Traldi Pietro , Vettori Umberto
Published: May 2005

The effects of performing ion resonance collisional activation in two steps separated by an intermediate phase were studied. The results show that the time duration and the tickle frequency setting used in this intermediate stage determine the phase of the tickle output in the second activation stage which it is essential to control, to ensure the efficiency of the activation process. The following interpretation is offered: the activation process can be efficiently resumed after a period of interruption, provided the tickle voltage in the second activation step is in‐phase with the axial motion of the ions induced by the tickle field during the first activation stage.
Electron impact mass spectrometry and metastable ion studies on 2‐[3‐hydroxy‐2‐pyridyi]‐2‐(3h)‐thiazolimine and 1,3,4‐thiadiazine derivatives
Authors: Hadjieva P. , Kalcheva V. , Tosheva M. , Danieli B. , Catinella S.
Published: May 2005

The mass spectrometric behaviour of some 2‐[3‐hydroxy‐pyridyl]‐2‐(3H)‐thiazolimine and 1,3,4‐thiadiazine derivatives was studied in detail under electron ionizing conditions by means of accurate mass measurements, deuterium‐labelling experiments and metastable ion studies. The resultant fragmentation patterns were highly complicated with cleavage of the amine bond and of the thiazoline ring. The main differences between the decomposition mechanism of thiazoline and thiadiazine derivatives lies in the retro‐synthetic ring transformation processes, observed in the case of thiadiazine compounds only.
Mass spectral fragmentation patterns of unsymmetric furylacrylic acid dicarbonyldichlorides and dianilides: 2,3‐dichloro‐3‐(5‐chloro‐carbonyI)‐2‐furyl‐acrylcarbonylchloride and 2,3‐dichioro‐3‐(5‐anilido‐2‐furyi)‐2‐acrylcarbonylanilide
Authors: Karminski‐Zamola Grace , Dogan Jasna , Bajić Miroslav
Published: May 2005

Electron ionization mass spectrometry is shown to provide a valid analytical toot for the structural characterization of the title compounds. Diagnostic fragmentation pathways of an unsymmetrically substituted 2,5‐furan dicarbonyl dichloride and dianilide were observed.
Analysis of clenbuterol in human plasma using liquid chromatography/atmospheric‐pressure chemical‐ionization mass spectrometry
Authors: Doerge Daniel R. , Bajic Steve , Lowes Steve
Published: May 2005

Clenbuterol is a β‐agonist drug used illegally as a growth stimulant in meat‐producing animals and human athletes. The analysis of clenbuterol in spiked human plasma was performed using on‐line liquid chromatography/atmospheric‐pressure chemical‐ionization mass spectrometry (LC/APCI‐MS) using a conventional bore LC column (flow rate = 1.0 mL/min). At low sampling cone voltages, the mass spectrum was predominantly the [M + H]+ ion but diagnostic fragment ions were formed upon incremental increases in sampling cone voltage. The detection limit (signal‐to‐noise ratio of 3) using selected‐ion monitoring of the [M + H]+ ion was 0.1 ng on‐column (l0 ppb). This is a 50‐fold better sensitivity of detection than that previously reported for an on‐line thermospray LC/MS method. The extraction procedures were not optimized for maximum sensitivity and the lack of interferences suggests that much lower detection limits for clenbuterol in plasma are attainable.
Electronic effects in the electron ionization fragmentations of 2‐aryl substituted octahydro‐1,3‐ and ‐3,1‐benzoxazines
Authors: Vainiotalo Pirjo , Lehtelä Pirjo‐Liisa , Fülöp Ferenc , Bernáth Gábor , Vuorilehto Lauri , Pihlaja Kalevi
Published: May 2005

The 70 eV electron ionization mass spectra of 27 2‐aryl substituted octahydro‐1,3‐ and ‐3,1‐benzoxazines have been recorded in order to find out how the site and stereochemistry of the ring fusion and especially the nature of the substitutent X on the 2‐phenyl group affect their fragmentation patterns. The structural isomers showed clearly different spectra; however, stereoisomeric differentiation was possible only with 1,3‐derivatives. The fragment‐ion peaks connected with the ionized ring and open chain forms of the compounds studied were clearly present in all the spectra. Analogously to the results obtained in solution, the electron‐withdrawing ability of X increased the abundance of the fragments originating from the ring form. Also, the relative importance of different fragmentation channels varied according to the electron donating or withdrawing ability of the substituent X.
Direct observation of UV‐crosslinked protein–nucleic acid complexes by matrix‐assisted laser desorption lonization mass spectrometry
Authors: Jensen Ole N. , Barofsky Douglas F. , Young Mark C. , Von Hippel Peter H. , Swenson Stephen , Seifried Steven E.
Published: May 2005

Interactions between proteins and nucleic acids arc important in the fundamental cellular processes that drive replication, recombination, dynamic alteration and repair of DNA, transcription and processing of RNA, synthesis of proteins, and regulation of enzyme activities. As part of an effort to develop a general, sensitive mass spectrometric strategy for the characterization of protein–nucleic acid interactions, we have used matrix‐assisted laser desorption‐ionization (MALDI) time‐of‐flight mass spectrometry to analyze protein–nucleic acid complexes that have been covalently crosslinkcd by ultraviolet (UV) light. In general, the application of MALDI mass spectrometric techniques to studies of U V‐induced crosslinking of nucleoprotein complexes is demonstrated to be feasible. Specifically, MALDI mass analysis was used to determine the molecular weights of the phage T4 gene 32 protein (gp32) crosslinked to the oligonucleotide (dT)20, and the Escherichia coli transcription termination factor rho, photoaffinity labeled with 4‐thio‐uridine‐diphosphate (4sUDP). The covalent gp32:(dT)20 complex is readily detected at a concentration of 1–2 μM in 1 μL of an unpurined solution of reactants thai has been exposed to a single, 266 nm UV laser pulse. Mass spectrometric molecular weight determinations of the covalent rho:4sUDP complex add directness and specificity to the ATPase inactivation assay normally used to monitor the formation of 4sUDP photoafluiity labeled rho. It is found that successful MALDI mass spectrometry of protein–nucleic acid complexes is as critically dependent on the choice of solvents and additives as it is on the primary matrix compound.
Isotope ratio measurements in lead using three‐photon one‐colour resonance ionization mass spectrometry
Authors: Telle H. H. , Telyatnikov A. L. , McNaghton E. D. , Brown R. A. , McCormick A.
Published: May 2005

Resonance effects on measured isotope ratios in lead using three‐photon one‐colour resonance ionization mass spectrometry are discussed. The shape of the ionization signal is considered for the case of a non‐monochromatic laser field. The intensity of the laser radiation is adjusted to be low enough not to cause saturation of the transitions. The variation of the measured isotope ratio as a function of laser frequency is considered. It is shown that the deviation of the measured from the expected isotope ratio, for a Lorentzian laser lineshape equals the ratio of the isotope shift to the laser bandwidth. Unfortunately, the background noise in the experiments makes verification of this behaviour difficult for the isotopes of low abundance.
Ion mobility spectrometry as a detection technique for the separation sciences
Authors: Jones Dennis , Brenton A. Gareth , Games David E. , Brittain Alan H. , Taylor Stephen , Kennedy David , Smith Peter
Published: May 2005

The development of a high temperature ion mobility, spectrometer is described for interfacing to chromatographic techniques, in particular, gas chromatography and high‐performance liquid chromatography. The performance of the system is assessed by measuring ion mobility constants for both positive and negative ions. The sensitivity of the detector was determined and found to allow the detection of trace components down to tens of picogrammes (pg) for halogenatcd compounds, in the negative‐ion mode of operation. Standard mixtures of potychlorinated biphenyls (PCBs) were studied by gas chromatography/ion mobility Spectrometry with the aim of quantitating extracts of soil samples. A novel method of interfacing to liquid chromatography has been evaluated using a membrane separator of large surface area and high efficiency for removing the mobile phase. Preliminary data for liquid chromatocraphy/ion mobility spectrometry is reported.
Electron‐ionization mass spectra of aminomethyltetrathiafulvalenes
Authors: Garín J. , Orduna J. , Uriel S.
Published: May 2005

Electron‐ionzation mass spectra of aminomethyltetrathiafulvalenes were studied by exact mass measurements and metastable‐ion analysis. Cleavages of the C‐N bond and the exocyclic C‐C bond with or without hydrogen rearrangement are the most characteristic fragmentations for these compounds. Ions at m/z 204 and 134 were characterized as tetrathiafulvalene and l,3‐dithiol‐2‐thione molecular ions by collisional activation.
Mass spectrometric location of double‐bond position in isomeric dodecenols, without chemical derivatization
Authors: Yuan Gu , He Meiyu , He Xiaoran , Horiike Michio , Kim Chul‐Sa , Hirano Chisato
Published: May 2005

A new procedure is presented for locating double‐bund position in dodecenols. Ten isomers of chemically unmodified dodecenol were analysed by two kinds of mass spectrometers. A series of spectra obtained with a magnetic sector instrument were interpreted by analysing the similarity of mass spectral patterns based on a ‘fuzzy’ reasoning method, in which the intensity ratios of six diagnostic pairs of the predominant ions were defined as standard parameters. The method was tested with other series of spectra from a quadrupole mass spectrometer, and the original double‐bond position in each isomer was located unambiguously.
Investigating the non‐covalent interaction of cytidylic acids, with Ribonuclease A by electrospray mass spectrometry
Authors: Camilleri Patrick , Haskins Neville J.
Published: May 2005

Electrospray mass spectrometry has been applied to probe the binding of 2′‐CMP,3′‐CMP and 2′3′‐CMP to RNaseA. Results show that, in the presence of excess amounts of these molecules, binding also appears to occur at a secondary site on the enzyme.
Quantitative aspects of the matrix‐assisted laser desorption mass spectrometry of complex oligosaccharides
Authors: Harvey D. J.
Published: May 2005

Comparative studies of the matrix‐assisted laser desorption ionization of complex oligosaccharides were made using a range of mono, di‐ and tri‐substituted benzoic acids, substituted coumarins and cinnamic acids. The best results were obtained with 2,5‐dihydroxybenzoic acid (2,5‐DHB). Detection limits using this matrix were in the range of 100 fmol for complex and high mannose sugars, some 2‐fold better than those obtained with α‐cyano‐4‐ hydroxycinnamic acid and 10‐fold better than with an earlier oligosaccharide matrix, 3‐amino‐4‐hydroxybenzoic acid. The strongest signals were achieved with a matrix‐to‐sample ratio of about 5000:1. Little correlation was found between the measured peak height and sample loading when 3‐amino‐4‐hydroxybenzoic acid was used as the matrix and the signal appeared to saturate at a sample level of around 30 pmol. However, good correlation was found between the amount of sample loaded onto the target and the response when an analogous compound was used as an internal standard and peak ratios were measured. In contrast to this, the use of 2,5‐dihydroxy‐benzoic acid as the matrix enabled the oligosaccharide to be measured over the range 100fmol to at least 100pmol with an excellent linear correlation between sample quantity and response and without the need of a standard. No evidence of saturation was found with this matrix. With 2,5‐DHB (other matrices were not tested), the oligosaccharide signal strength was found to fall with increasing molecular weight in a linear manner and similar to that found previously with proteins. Signal strength from individual sugars also fell when these were measured in mixtures. Derivatization (peracetylation) generally caused an increase in signal strength.
Electron impact ionization of H2O ice
Authors: Safvan C. P. , Raheja U. T. , Mathur D.
Published: May 2005

Electron impact ionization and dissociative ionization of water in vapour and ice form has been studied using a newly developed apparatus comprising a well‐collimated beam of 700 eV electrons, a cryogenic target assembly and a quadrupole mass spectrometer. The target assembly consists of a liquid‐nitrogen cooled nickel foil upon which a thin layer of ice is formed. Comparison of the vapour‐phase mass spectrum with that obtained in the ice phase reveals significant differences in the dissociative ionization pattern which are of significance in modelling studies of cold astrophysical environments.
Doubly charged ions: Differentiation of flavanone and 2′‐hydroxy chalcone
Authors: Vékey Károly , Szabó Pál , Dinya Zoltán
Published: May 2005

The metastable and collision‐induced decompositions of the singly charged molecular ions of flavanone and of 2′‐hydroxy chalcone were obtained using mass‐analysed ion kinetic energy spectrometry. Using the same method, neutral losses from, and charge separation reactions of, the doubly charged molecular ions were also determined. The fragmentation characteristics of the doubly and singly charged ions were found to be completely different. Comparison of the spectra of the isomers indicated that both the reactive and unreactive singly charged molecular ions lose their structural identity by the time they reach the second field‐free region; flavanone ions probably isomerize to 2′‐hydroxy chalcone ions. The corresponding doubly charged molecular ions, on the other hand, do not isomerize, and their spectra are quite distinct. This result suggests that spectra of doubly charged ions may, in some cases, be more suitable for the characterization of isomers than singly charged ions.
Ion trap and quadrupole mass spectra of lignin pyrolysates: How well do they compare?
Authors: Galletti Guido C. , Reeves James B. , Francis Barry A. , Reeves Valerie B.
Published: May 2005

Lignin samples from wheat straw, orchard grass, red clover and a synthetic lignin were subjected to pyrolysis gas chromatography/mass spectrometry using both quadrupole (QMS) and ion‐trap detector (ITD). ITD mass spectra were comparable with those presented in the National Bureau of Standards (NBS) library and with those obtained by QMS as evaluated by discrepancy factors. Computer‐assisted library searches for ITD spectra were successful for 22 of 47 compounds. The other 25 compounds were not present in the library. A typical program and mass spectra are shown. Statistical data are discussed.
Fast‐atom bombardment mass spectrometric study of some N‐ and S‐glycosides of acetylated hexose isomers
Authors: Liptáak Miklós , Heerma Wigger
Published: May 2005

Various N‐aryl, S‐aryl and S‐alkyl glycosides of acetylated D‐glucose, D‐galactose and D‐mannose have been studied by fast‐atom bombardment mass spectrometry. It was found that the matrix used has a considerable effect on the relative peak intensities in the molecular mass region. Glycerol apparently promotes the formation of protonated molecules (MH+) whereas in 3‐nitrobenzyl alcohol both MH+ ions and M+· radical cations are abundant. The unimolecular decomposition spectra of the MH+ ions exhibit two significant peaks corresponding to losses of acetic acid and of the aglycon. The intensity ratios of these fragment ions are dependent on the nature of the aglycon and the hexose unit and can be used to identify the monosaccharides. It has also been established that acetic acid elimination occurs mainly from the C‐3 position.
Time‐base modulation for the correction of cyclotron frequency shifts observed in long‐lived transients from fourier‐transform ion‐cyclotron‐resonance mass spectrometry of electrosprayed biopolymers
Authors: Bruce James E. , Anderson Gordon A. , Hofstadler Steven A. , Winger Brian E. , Smith Richard D.
Published: May 2005

The occurrence of small shifts in the cyclotron frequency during the acquisition of very long transients (in excess of 80 s) has been observed to be a limiting factor for ultrahigh‐resolution mass measurements of protein ions performed with electrospray‐ionization Fourier‐transform ion‐cyclotron‐resonance mass spectrometry. Resolution measurements were restricted to values less than 106 because of the frequency shifts. Measurements of the frequency shifts, performed by sequentially transforming small segments of the transient, allowed the shift to be characterized and fitted to a 4th‐order equation. The sampling rate of the acquired transient was then modulated (at a rate equal to the reciprocal of the rate for the frequency shift) to allow ultrahigh resolution, greater than 2 × 106, and improved mass measurement and precision to be achieved for a small protein.
Reactions of low‐energy ions with ferrocene self‐assembled monolayer surfaces
Authors: Pradeep T. , Riederer D. E. , Ast T. , Cooks R. G.
Published: May 2005

Collisions of low‐energy Cr(CO) (n = 0, 2, 6) ions with self‐assembled monolayer surfaces bearing covalently bound ferrocene groups result in transfer of the cyclopentadienyl ligand into the gas phase as the Cr(C5H5)+ ion. High fluences of Cr+ ions lead to deposition of Cr at the surface and subsequent Xe+ collisions liberate the metal ion. The Cr atoms deposited on the surface appear to be chemically bonded to the cyclopentadienyl rings. The implications of these results for modification of surfaces using ion beams are discussed.
Multiple excitation collisional activation in Fourier‐transform mass spectrometry
Authors: Lee Samuel A. , Jiao Charles Q. , Huang Yongqing , Freiser Ben S.
Published: May 2005

Multiple excitation collisional activation (MECA) has been examined using Fourier‐transform mass spectrometry. In analogy to recently reported multiple excitation detection schemes, MECA is a process in which ions are translationally excited to larger orbits by applying an RF signal over the desired mass range. Next, collisional cooling of the ions collapses them, spatially, back to the center of the cell, where the process can be repeated. Two examples of the utility of MECA are given. The first involves a novel way of growing cluster ions by sequential ion/molecule reactions followed by MECA. The second uses MECA to increase the energy deposition in a stable and difficult‐to‐fragment ion, thereby inducing fragmentation.
Bond activation by d0 metal carbene complexes in the gas phase
Authors: Wilson Kimber L. , Cooper Brian T. , Buckner Steven W.
Published: May 2005

The formation and bond activation reactions of the d0 carbene complexes MCHCN+ (M = Sc, Y) are presented. Sc+ and Y+ dehydrogenate acetonitrile to produce the metallocarbenes. The carbene complexes are less reactive towards hydrocarbons than their bare metal ion counterparts, but will activate CH, OH, and NH bonds through a four‐centered intermediate. Labeling studies indicate that reactions with olefins proceed by migratory insertion after initial CH activation, and that subsequent ligand coupling produces metal‐bound nitrite products. Oletin metathesis reactions are not observed due to the electron‐withdrawing characteristics of the CN substituent and the electrophilicity of the metal centers.
Metastable ion study of organosilicon compounds, part VII.1 Losses of C2H4 and CH4 from the metastable dimethylsilyl ion [(CH3)2Si+H]
Authors: Tabei Eiichi , Mori Shigeru , Kinoshita Takeshi , Kawazoe Kayoko , Tajima Susumu
Published: May 2005

The spontaneous unimolecular dissociative reactions of dimethylsilyl cations (CH3)2Si+H (1+; m/z 59) have been investigated by mass‐analyzed ion kinetic energy (MIKE) spectrometry and deuterium‐labelling studies. Excepting the losses of H and H2, the ions 1+ mainly eliminate C2H4 and CH4 to produce product ions at m/z 31 and 43, respectively. Almost complete hydrogen scrambling occurs prior to the C2H4 loss, but only a small degree of scrambling occurs in the CH4 loss. Predominantly, the hydrogen atom bound to Si participates in the latter reaction, contrary to the previously reported mechanism.
Mass spectra of some phenylphosphinosilanes
Authors: Kim Tae Wook , Jahng Woong Sang , Kim Chang Hwan , Lee Myong Euy
Published: May 2005

The 70 eV electron‐impact low resolution spectra of Me3SiPPh2, (Me3Si)3SiPPh2, and (Me3Si)2(Me)SiP(Me)(Ph) were investigated. The migration of two phenyl groups from phosphorous to a silicon site was observed and the unimolecular mass‐analysed ion kinetic energy spectra indicated that the migration occurred in [M  CH3]+ ions rather than in M+· ions. The benzene eliminations from the M+· and [M  CH3]+ ions of Me3SiPPh2 were observed not in the EI spectrum, but in their MIKE spectra.
Mass spectrometric sequencing of linear peptides by product‐ion analysis in a reflectron time‐of‐flight mass spectrometer using matrix‐assisted laser desorption ionization
Authors: Kaufmann R. , Spengler B. , Lützenkirchen F.
Published: May 2005

In matrix‐assisted laser desorption ionization (MALDI) a large fraction of analyte ions undergo post‐source decay (PSD) during flight in the field‐free drift path. By means of a modified two‐stage reflectron, product ion time‐of‐flight spectra of medium‐sized linear peptides (up to 2800 u) were recorded, containing full sequence information. Precision, accuracy and mass resolution of fragment ions were almost as good as obtained in high‐energy collisionally activated dissociation (CAD) studies performed in four‐sector instruments. Instrumental sensitivity was better by at least one order of magnitude. In reflectron time‐of‐flight mass spectrometry (RETOF‐MS) the cleavage pattern of PSD products is different from that obtained by high‐energy and low‐energy CAD. Activation mechanisms of PSD were found to be largely determined by collisional events (ion/neutral) occurring in the acceleration field during early plume expansion. Future potentials of PSD analysis after MALDI are discussed.
Selected‐ion accumulation from an external electrospray ionization source with a fourier‐transform ion cyclotron resonance mass spectrometer
Authors: Bruce James E. , Anderson Gordon A. , Hofstadler Steven A. , van Orden Steven L. , Sherman Michael S. , Rockwood Alan L. , Smith Richard D.
Published: May 2005

The coupling of an electrospray ionization (ESI) source to a Fourier‐transform ion cyclotron resonance (FTICR) mass spectrometer provides a facility for the high resolution, accurate mass analysis of large biopolymers. Typically the m/z range of the electrosprayed ions injected and trapped in the FTICR cell is between m/z 500 and 2500 (but can vary considerably with solution conditions). Recent reports on quadrupole excitation have demonstrated the ability to cool the magnetron motion of ions trapped in the FTICR mass spectrometer cell by converting this motion to cyclotron motion which, under appropriate pressure conditions, damps readily to the center of the cell. The use of a broadband waveform (swept frequency or stored waveform inverse Fourier‐transform) for the quadrupole cooling pulse was shown to provide cooling of a wide range of m/z ions, while implementation of a single frequency demonstrated a much narrower m/z response. This report demonstrates the successful combination of single‐frequency quadrupole cooling with external injection of electrosprayed ions into an FTICR mass spectrometer for m/z selected‐ion accumulation. This capability is particularly significant with electrospray ionization since it allows ions of only one charge state to be accumulated in the cell, and greatly increases the potential dynamic range of ESI‐FTICR.
Jet separator/membrane introduction mass spectometry for on‐line quantitation of volatile organic compounds in aqueous solutions
Authors: Dejarme L. E. , Bauer S. J. , Cooks R. G. , Lauritsen F. R. , Kotiaho T. , Graf T.
Published: May 2005

A new technique is described for the direct detection of volatile organic compounds present in aqueous solutions at levels in the parts per trillion range. The sample is enriched in analyte in two consecutive stages; one utilizes a semi‐permeable membrane interface and the other a jet separator. The analyte solution is sampled as it flows coaxially over a semi‐permeable capillary membrane, the interior of which is continuously purged by helium. The permeate is pneumatically transported to the mass spectrometer via a jet separator, which is used to remove excess helium and 'vater from the analyte vapor strean. Data are reported for two instruments; in one the membrane/jet separator system is interfaced to a single ijuadrupolc mass spectrometer via a custom‐built metal jet separator with a variable capillary gap. In the second, an ion‐trap mass spectrometer is used in conjunction with a conventional fixed‐gap quartz jet separator. Typical analyte response times are 2–5 min at ambient temperature, and Mow injection methods are used for sample delivery. Direct comparisons, made under identical instrumental conditions, show that the jet separator system displays even lowsr detection limits than a conventional direct‐insertion membrane probe. Detection limits in the range 30 parlis per trillion to a few parts per billion are observed for selected volatile organic compounds and the response is linear over 3 orders of magnitude.
Analysis of the squalestatins by on‐line packed capillary liquid chromatography combined with electrospray mass spectrometry
Authors: Lane S. J. , Brinded K. A. , Taylor N. L. , Watkins P. J. F. , Harrison M. E.
Published: May 2005

A mixture of four squalestatins was separated anil characterized by gradient packed capillary liquid chromatography combined with electrospray collision‐induced dissociation mass spectrometry (ESI/CID/MS). Negative‐ion ESI was found to afford spectra typified by strong pseudo‐molecular ions but providing little structural information. Structural information was obtained using an ion‐focusing RF‐only octapole lens to provide conditions for CID. The new method showed improvements in sensitivity when compared to existing thermospray and dynamic liquid secondary‐ion mass spectrometry methods.
Application of a parallel computer to simulation of ion trajectories in an ion cyclotron resonance spectrometer
Authors: Miluchihin Nickolay V. , Miura Kenji , Inoue Masao
Published: May 2005

A parallel computer was used to calculate ion trajectories in the cell of an ion cyclotron resonance spectrometer. Computation was carried out 512 ions simultaneously. Ion‐cloud evolution in a non‐uniform electric field and ion/neutral collision processes were introduced to demonstrate the capability of parallel computation. The performance evaluation of a parallel computer was fulfilled.
Electron affinities of higher fullerenes
Authors: Boltalina O. V. , Sidorov L. N. , Ya. Borshchevsky A. , Sukhanova E. V. , Skokan E. V.
Published: May 2005

Knudsen cell mass spectrometry has been used for the investigation of ion‐molecule equilibria between gaseous neutral species and negative ions in fullerenc vapors at 800–900 K. Equilibrium constants of one‐electron exchange reactions between C60 and the higher fullerenes C70, C76, C78 and C84 have been measured. Electron affinities of C70, C76, C78 and C84 were found to be 2.72 ± 0.05, 2.88 ± 0.05, 3.01 ± 0.07, and 3.05 ± 0.08 eV respectively. Negative ions of C86, C90, and C92 were observed, and the lower limit of electron affinities for these species was estimated as ≥3.0eV.
Small volume and low flow‐rate electrospray lonization mass spectrometry of aqueous samples
Authors: Gale David C. , Smith Richard D.
Published: May 2005

A new electrospray ionization source (emitter) has been developed which allows the effective utilization of very small sample volumes at much lower flow rates than previously demonstrated. A small diameter etcched‐tip capillary has been incorporated into a pressure‐infusion electrospray ionization source. The ability to electro‐spray aqueous solutions without the use of an ancillary sheath flow is demonstrated with several biopolymers. High signal intensities and stable signals are observed for this source in a comparison with a standard methanol‐sheath source.
A curved‐field reflectron for improved energy focusing of product ions in time‐of‐flight mass spectrometry
Authors: Cornish Timothy J. , Cotter Robert J.
Published: May 2005

A new type of curved‐field reflectron has been developed for the energy focusing of ions formed after initial acceleration in time‐of‐flight (TOF) mass spectrometers. These include ions generated in the dissociation region of a tandem TOF, as well as metastable decay products formed in the field‐free drift region prior to their reflection. Unlike conventional linear‐field reflectrons, which focus product ions to different focal lengths that are proportional to the mass (energy) of the fragment, the new curved‐field reflectron energy focuses all ions to within a small region near the exit of the reflectron. Thus, the collection of resolved fragment peaks is possible without scanning or stepping the potential gradient of the reflectron, enabling faster acquisition of the production spectrum and, more importantly, true multiplex recording of the spectra from each ionization event. Theoretical considerations of the design are discussed along with an evaluation of collision‐induced dissociation data, demonstrating the performance of the new reflectron in a tandem TOF instrument.
Facile identification by electrospray mass spectrometry of the insulin fragment A14–21‐B17–30 produced by insulin proteinase
Authors: Vu Lan , Stöcklin Reto , Rose Keith , Offord Robin E.
Published: May 2005

We confirm the cleavage at position B16–17 of porcine insulin which occurs during in vitrio digestion by insulin proteinase. The fragment A14–21‐B17–30 was purified by reversed‐phase high performance liquid chromatography and characterized by electrospray ionization mass spectrometry. Fast‐atom bombardment mass spectrometry, on the other hand, failed todetect the presence of this fragment.
Characterization of succinimide‐type dehydration products of recombinant hirudin variant 1 by electrospray tandem mass spectrometry
Authors: Grossenbacher H. , Märki W. , Coulot M. , Müller D. , Richter W. J.
Published: May 2005

Two congeners Q4 and Q5 inferred in earlier analyses to be cyclic succinimide‐type dehydration product; of recombinant hirudin (variant 1) were structurally fully characterized. After isotopic labeling by ring‐opening with H218O, the suspected anhydro‐positions Asp53 and Asp33 were confirmed by tandem mass spectrometry (MS/MS) sequencing of relevant smaller peplides directly in the enzymatic hydrolysates (V8 protease) using electrospray MS/MS. The chosen strategy proved highly efficient and sensitive.
Direct peptide mapping of sickle‐cell hemoglobin using electrospray mass spectrometry
Authors: Sakairi Minoru
Published: May 2005

Direct peptide mapping of sickle‐cell hemoglobin (Hb S) using electrospray mass spectrometry is demonstrated to be a rapid, sensitive and useful technique for providing information concerning the location of variation. By fully comparing electrospray mass spectra of digests of sickle‐cell and normal hemoglobins, using L‐l‐tosylamide‐2‐phenylethyl chloromeihyl ketone (TPCK)‐treated trypsin, the point mutation of B1 fragment of β‐chain in Hb S can be confirmed, taking into consideration that all the other fragments are completely identical in the two proteins.
Identification of double‐bond position in the sex pheromone of china corn borer by mass spectrometry
Authors: Yuan Gu , He Meiyu , He Xiaoran
Published: May 2005

The female sex pheromone of the China corn borer, Ostrinia furnacalis (Lepidoptera: Pyralidae), was confirmed as Δ12‐tetradecenyl acetate by a ‘fuzzy’ similarity analysis of gas chromatograph/mass Spectrometry data.
Mass spectral fragmentation reactions of some stereoisomeric cyclic β‐amino acids under electron and chemical ionization
Authors: Partanen Tuula , Vainiotalo Pirjo , Stájer Géza , Bernáth Gábor , Göndös György , Pihlaja Kalevi
Published: May 2005

Mass spectral fragmentations of two cyclopentane, four cyclohexane/ene and four norbornane/ene ß‐amino acids were studied under electron ionization by low‐resolution, high‐resolution, metastable ion analysis and collision‐induced dissociation techniques. All stereoisomeric compounds gave rise to identical 70 eV electron‐ionization mass spectra. The major fragmentation pathway for the saturated compounds began as an α‐cleavage reaction with respect to the nitrogen atom. For the unsaturated compounds, a retro‐Diels–Alder reaction was favoured. In addition to a normal retro‐Diels‐Alder fragmentation reaction, the norbornene compounds underwent a retro‐Diels‐Alder fragmentation reaction accompanied by the migration of one hydrogen atom. In the case of the chemical ionization mass spectra, differences between stereoisomers were observed only under methane chemical ionization, where monocyclic trans isomers decomposed more readily than the corresponding cis isomers. All the [M + H]+ ions decomposed mainly by dehydration and deamination reactions. The fragmentation in the chemical‐ionization ion source resulted in the same elimination ratio [M + H  H2O]/{[M + H  H2O] + [M + H  NH3]} as observed under kinetic control in the collision region.
Computer‐Designed waveform technique for reducing chemical noise in atmospheric‐pressure ionization/ion‐trap mass spectrometry
Authors: Mordehai Alex V. , Henion J. D.
Published: May 2005

This paper describes implementation of a storage waveform technique for manipulation of ions in a quadrupole ion trap. The technique is similar to the well established storage waveform inverse Fourier‐transform (SWIFT) technology for controlling ion motion in Fourier‐transform ion cyclotron resonance (FT‐ICR). These techniques allow one to manipulate ions stored in the trap through computer control. The focus of this paper is the application of the storage waveform technique to the chemical noise problems associated with the analytical applications of atmospheric‐pressure ionization/ion‐trap mass spectrometry. In particular, the wave function described results in selected‐ion accumulation in the trap in a mass window of ∼︁ 100 u. The position of the mass window can easily be adjusted across the mass range, thus providing selective accumulation in the trap only for ions of interest, while removing all others. The technique is easily implemented for routine use with on‐line separations, resulting in improved sensitivity by significantly reducing ion current from interfering chemical background.
Mass spectrometric studies on azasqualenes, a class of 2,3‐oxidosqualene cyclase inhibitors
Authors: Ceruti Maurizio , Seraglia Roberta , Traldi Pictro
Published: May 2005

The mass spectrometric behaviour of a series of azasqualenes and azasqualanes has been studied by two different instruments, a double focusing machine and an ion‐trap mass spectrometer (ITMS). The high abundances of fragmentation products obtained using the former indicate that with ITMS, processes additional to electron ionization must be present, leading to molecular species with lower internal energy contents.
Matrix‐assisted laser desorption ionization for rapid determination of the sequences of biologically active peptides isolated from support‐bound combinatorial peptide libraries
Authors: Scott Youngquist R. , Fuentes Gary R. , Lacey Martin P. , Keough Thomas , Baillie Thomas A.
Published: May 2005

A termination synthesis approach has been developed to encode each resin bead in support‐bound combinatorial peptide libraries with the information needed to establish the sequence of the full‐length products also contained on the beads. Matrix‐assisted laser desorption ionization mass spectrometry was then used to rapidly read the appropriate sequences. In addition to rapid peptide sequencing, the technique allows direct assessment of the quality of the synthetic library, since deletion peptides, side‐reaction products and incomplete‐deprotection products are readily observed. An anti‐gp120 monoclonal antibody was screened against a hexapeptide library, and eight active peptides were isolated. Six of the eight peptides were shown to possess the exact recognition sequence for the antibody.
Analysis of fumonisin B1 by negative‐ion thermospray mass spectrometry
Authors: Thakur Rohan A. , Scott Smith J.
Published: May 2005

Thermospray mass spectrometry was used to analyze fumonisin B1 (FB1) from two corn samples that were known to contain fumonisins, and from a FB1‐spiked meat sample. The mass spectrometer was operated in the negative‐ion discharge‐on, filament‐off, mode with the fragmentor set at 200 V. Selected‐ion monitoring (SIM) was used for quantitative analysis. The mobile phase was CH3CN (containing 1% CICH2CN, v/v)+0.1M ammonium acetate, pH 3.65 (65:35, v/v). Quantitative analysis was done by integrating the peak areas traced by ion currents of 5 selected ions in SIM, and by the method of standard additions. Responses to the selected ions were linear within the range of 2‐200 ng. Fumonisins were easily identified in the corn and muscle tissue matrices without any apparent matrix interferences and were detectable down to 0.1 μ/mL (2 ng injected).
Identification of phosphorylated peptides from complex mixtures using negative‐ion orifice‐potential stepping and capillary liquid chromatography/electrospray ionization mass spectrometry
Authors: Ding Jianmei , Burkhart William , Kassel Daniel B.
Published: May 2005

A rapid method for identifying and characterizing sites of phosphorylation of peptides and proteins is described. High‐performance capillary liquid chromatography (HPLC) coupled with electrospray ionization mass spectrometry (ESI‐MS) is used to distinguish non‐phosphorylated and phosphorylated peptides originating from mixtures as complex as enzyme digests. The method relies on the ability to produce a fragment ion characteristic and unique to phosphopeptides (m/z 79, PO3−) by stepping the orifice potential of the mass spectrometer as a function of mass. At low m/z values, a high orifice potential is applied to induce extensive fragmentation of the peptide, leading to the formation of the m/z 79 phosphate‐derived ion. This method is analogous to that described by Carr et al. for the identification of glycopeptides from enzymatic digestion of glycoproteins (S.A. Carr, M. J. Huddleston, M. F. Bean, Protein Science 2, 183 (1993)). The method was first evaluated and validated for a mixture of non‐, mono‐ and di‐phosphorylated synthetic peptides. Both mono‐ and di‐phophorylated peptides were found to generate fragment ions characteristic of PO3− whereas the non‐phosphorylated peptide did not. Application of the method was extended to identifying phosphopeptides generated from an endoprotease Lys‐C digestion of β‐casein. Both the expected mono‐ and tetra‐phosphorylated Lys‐C peptides were observed and identified rapidly in the LC/SEI‐MS analysis. The procedure was used additionally to identify the site(s) of phosphorylation of the cytosolic non‐receptor tyrosine kinase, pp60c‐src.
Capillary column supercritical fluid chromatography/mass spectrometry of polycyclic aromatic compounds using atmospheric pressure chemical ionization
Authors: Thomas Darren , Greig Sim P. , Benoit Frank M.
Published: May 2005

Capillary column supercritical fluid chromatography (SCF) was combined with atmospheric pressure chemical ionization (APCI) mass spectrometry through a heated pneumatic‐nebulizer interface, originally developed for liquid chromatography/mass spectrometry (LC/MS), and subsequently modified for use with supercritical fluid chromatography/mass spectrometry (SFC/MS). A high pressure syringe pump was used to pass SFC‐grade carbon dioxide, used as the mobile phase, through a capillary SFC column which was contained in an oven, maintained at 100°C. The eluent passed through the heated pneumatic‐nebulizer interface into the ionization region of the mass spectrometer with the aid of the flow of nebulizing gas. The system was optimized using benz[a]anthracene, and then applied to analyze a standard mixture of polycyclic aromatic compounds (PACs) as well as complex mixtures of PACs obtained by the fractionation of a pond sediment contaminated by coke‐oven residues. A detection limit of 40 pg was established for chrysene.
The evaluation of several electrospray systems and their use in non‐covalent bonding studies
Authors: Haskins Neville J. , Ashcroft Alison E. , Phillips Andrew , Harrison Mark
Published: May 2005

A number of different designs of electrospray sources have been used to study the non‐covalent interaction between ribonuclease A and cytidylic acids. Signal differences were observed between the various types of source giving rise to very different spectra. However, in all cases, information was obtained relating to the putative complex.
Electrospray tandem mass spectrometry in the diagnosis of organic acidemias
Authors: Rashed M. S. , Ozand P. T. , Harrison M. E. , Watkins P. J. F. , Evans S. , Baillie Thomas A.
Published: May 2005

A novel procedure based on electrospray tandem mass spectrometry (ESI‐MS/MS) has been used in the diagnosis of organic acidemias. The method is based on the determination of acylcarnitine profiles from blood spots collected on Guthrie cards. The acylcarnitines are extracted with methanol, derivatized to their butyl esters and analyzed by ESI‐MS/MS. Precursor‐ion scanning of the common fragment at m/z 85 of the butyl esters yields highly diagnostic acylcarnitine profiles. Analysis time is one minute per sample and is fully automated. Examples are given of normal profiles, of profiles from two patients with fatty acid oxidation defects, and of a case of propionic acidemia. The technique is simple, rapid and specific, and shows potential for routine application in neonatal screening of organic acidemias.
1994 Directory of mass spectrometry manufacturers and suppliers
Authors: Lammert Stephen A.
Published: May 2005

An annual directory of companies which supply mass spectrometers and mass spectrometry components and services.
Quantitative determination of β(1–2) cyclic glucans by matrix‐assisted laser desorption mass spectrometry
Authors: Garozzo Domenico , Spina Emanuela , Sturiale Luisa , Montaudo Giorgio , Rizzo Roberto , Daolio S.
Published: May 2005

The use of matrix‐assisted laser desorption/ionization mass spectrometry for the determination of the molecular weight distribution of cyclic β (1–2) glucans is reported here. Quantitative response is demonstrated by the use of different instruments and by comparison with high‐performance liquid chromatography/refractive index detection analysis.