bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of glucopyranosyl‐β‐1,4‐glucopyranosyl‐β‐1‐N‐oxindole‐3‐acetyl‐N‐aspartic acid, a new IAA catabolite, by liquid chromatography/tandem mass spectrometry
Authors: Östin Anders , Catalá Carmen , Chamarro Jesus , Sandberg Göran
Published: May 2005

[5‐3H,13C6] Indole‐3‐acetic acid was fed to immature pericarp segments from fruits of tomato (Lycopersicon esculentum Mill., cv. Moneymaker), resulting, after 24 h of incubation, in five radiolabelled peaks when analysed by reversed‐phase high‐performance liquid chromatography with radiocounting. The fractions were numbered in order of decreasing polarity. Fractions 4 and 5 had earlier been shown to contain indole‐3‐acetyl‐N‐aspartic acid and indole‐3‐acetyl‐O‐glucose. Based on results from strong alkaline hydrolysis, it had been concluded that fractions 1 and 3 contain an amide conjugate with a modified indole ring. This paper presents data supporting the structure of the labelled compounds in fractions 1 and 3 to be diastereomers of glucopyranosyl‐β‐1,4‐glucopyranosyl‐β‐1‐N‐oxindole‐3‐acetyl‐N‐aspartic acid. The identification of glucopyranosyl‐β‐1‐N‐oxindole‐3‐acetyl‐N‐aspartic acid in fraction 2 is also reported. These structures were elucidated by liquid chromatography/frit fast atom bombardment tandem mass spectrometry.
Quantitation of fatty acids and hydroxy fatty acids by gas chromatography/mass spectrometry. Predictively useful correlations of relative response factors with empirical formula
Authors: Chaurasia Chandra S. , Williams Todd D. , Judson Charles M. , Hanzlik Robert P.
Published: May 2005

Relative response factors (molar sensitivities relative to dibutyl phthalate) for homologous series of n‐alkanes (C12C26), trimethylsilyl esters of C10C20 fatty acids (FAs) and bistrimethylsilyl derivatives of C8C16 ω‐hydroxy fatty acids (HOF As) were determined by integration of total ion chromatograms obtained using a conventional gas chromatograph‐mass spectrometer in the electron impact ionization mode. For the alkanes up to C22 and for the FA‐TMS derivatives up to C18 (C21 including the TMS carbons), response factors increased linearly with total number of carbons (r2 > 0.99). The slope of this correlation (response factor = 0.0775n − 0.338, where n is the total number of carbon atoms in each analyte) is essentially identical with those determined in earlier studies for smaller molecules not containing silicon. For the HOFA derivatives up to C14 (C20 including TMS carbons), the molar response factors also increased linearly with total number of carbons, but for reasons not yet apparent the regression line for these homologs was different (response factor = 0.0330n + 0.456; r2 > 0.99). Response factors for higher homologs in all three series fell below the regression line for the lower homologs, the deviation increasing with increasing molecular mass and increasing GC retention time. In all three series the upper limit to the linear portion of the correlation corresponded to the homolog whose GC retention time was ca 15 min under the conditions used; a high injection port temperature was found to be the most critical factor in extending the linear range of the correlation.
Electron impact behaviour of trans‐4‐benzoylamino‐2H‐1‐benzopyran‐3‐ols: Evidence for an oxygen migration with loss of a benzopyranone
Authors: Evans John M. , Organ Andrew J. , Sims Jonathan L.
Published: May 2005

Certain abundant peaks in the electron impact mass spectra of a series of trans‐4‐benzoylamino‐2H‐1‐benzopyran‐3‐ols involve the formation of a substituted N‐alkylated benzonitrile ion by a mechanism involving migration of oxygen, in a postulated four‐centre skeletal rearrangement, leading to the loss of a benzopyranone. The presence of a small range of differing substituents at three locations in this series was studied for their effects on this proposed mechanism.
Intramolecular aromatic substitution and amino‐Claisen rearrangement in substituted N‐(2‐propynyl)anilines on electron impact
Authors: Ramana D. V. , Sudha M. S.
Published: May 2005

N‐(2‐Propynyl)anilines undergo amino‐Claisen rearrangement to a minor extent in the ion source, losing a molecule of HCN under electron impact conditions. However, metastable molecular ions with energies closer to threshold undergo Claisen rearrangement giving rise to more abundant [M − HCN]+· ions in the first field‐free region. Loss of a hydrogen from the molecular ion gives rise to the base peak in the mass spectrum of N‐(2‐propynyl)aniline. The hydrogen that is expelled for the formation of the [M − H]+ ion is observed to be from the amino nitrogen, propargylic carbon and the ortho‐carbon of the ring. The last process leads to a cyclic fragment involving intramolecular aromatic substitution. Double oxygen migration from the nitro group to the triple bond, due to the ortho effect, yields an abundant ion at m/z 105 in N‐(2‐propynyl)‐o‐nitroaniline. The proposed fragmentation pathways and ion structures are substantiated by high‐resolution data, B/E and B2/E linked‐scan spectra, collisionally activated dissociation–B/E linked‐scan spectra and deuterium isotopic labelling.
Application of reversed phase liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry to the determination of polycyclic aromatic sulfur heterocycles in environmental samples
Authors: Thomas Darren , Crain Sheila M. , Sim P. Greig , Benoit Frank M.
Published: May 2005

Reversed‐phase liquid chromatography (RPLC) was combined with atmospheric pressure chemical ionization mass spectrometry (APCI‐MS), via a heated pneumatic nebulizer interface, for the determination of the polycyclic aromatic sulfur heterocycle (PASH) content of samples obtained by the fractionation of an extract of a pond sediment contaminated by coke‐oven residues. Some of the samples produced by the fractionation procedure contained large amounts of other polycyclic aromatic compounds (PACs) which co‐eluted with the compounds of interest, making it difficult to obtain mass spectra suitable for compound identification and verification. Therefore, the use of tandem mass spectrometry (MS/MS), as a selective method for the identification of target analytes in complex matrices, was investigated. Initially, PASH standards were injected into the mass spectrometric system by flow injection and their collisionally induced dissociation mass spectra recorded. From these results, it was possible to select ions suitable for selected reaction monitoring (SRM) experiments on both the PASH standards (to establish detection limits and also retention times which could be used to identify these compounds) and the fractions (to establish the possible presence of the selected PASHs in the fractions). The RPLC‐SRM experiments led to a tentative identification of some of the PASH standards in the fractions. However, the use of multiple reaction monitoring experiments allowed the positive identification of dibenzothiophene, phenanthro [4,5‐bcd] thiophene, phenanthro [3,4‐b] thiophene and benzo [b] naphtho [2,3‐d] thiophene in the fractions, along with several of their isomers. Quantification of the PASH standards by RPLC‐SRM in the extracts found them to be present at high levels.
Glucose glass films: A matrix for mass spectrometry that mimics aqueous solution behavior
Authors: Song Siqing , Macfarlane Ronald D.
Published: May 2005

This study demonstrates that an amorphous film of glucose has many of the features of water as a medium for solvating ions and, at low concentrations, maintaining ion pair separation. Aqueous solutions of glucose containing dissolved salts are evaporated to form a homogeneous glucose glass where the distribution of the solute in solution is preserved in the evaporated glass film. Cluster ions form in aqueous solutions at high solute concentration, and glucose films made from these solutions form gas‐phase cluster when the film is excited by a high energy density pulse. These cluster ions do not form in dilute solutions and are not present in the mass spectrum of ions desorbed from films prepared from these solutions. Non‐polar ions concentrate at the surface of aqueous solutions owing to the hydrophobic interaction and glucose glass films prepared from these solutions show, by mass spectrometry, that these features are retained in the glucose film. The salts studied include KCl, NaBr, LiCF3SO3, (tert‐butyl)4NI and (C2H5)4NBF4. The concentration of the salt is the important variable in the study and ranges from a mole fraction of 0.1–10−4. For non‐polar ions, the abundance of the molecular ion is not significantly changed over a wide range of dilutions.
Determining calcium‐binding stoichiometry and cooperativity of parvalbumin and calmodulin by mass spectrometry
Authors: Hu Peifeng , Loo Joseph A.
Published: May 2005

The calcium‐binding properties of parvalbumin and calmodulin were investigated by electrospray ionization mass spectrometry (ESI‐MS). The two calcium sites of parvalbumin were found to be strongly cooperative in binding Ca2+ ion. Up to four calcium ions were found to bind to calmodulin at high calcium concentration levels. Strong cooperativity was detected between the third and fourth Ca2+ binding sites of calmodulin (ordered by loading sequence). Strong interactions were also indicated between the two halves of the calmodulin molecule. Demetallation of the gas‐phase ions can occur during the desolvation process, especially for ESI of aqueous solutions. However, the ESI‐MS methodology has the potential to provide insight into the intricate processes involved in metal site communications for other metalloproteins.
Effects of molecular geometry on the fragmentation of ionized maleic and fumaric acids; an overdue reappraisal
Authors: Chen Hongwen , Holmes John L.
Published: May 2005

The ionized geometric isomers maleic and fumaric acids ((Z)‐ and (E)‐ethenedicarboxylic acids) were studied by a variety of tandem mass spectrometric techniques. In agreement with much earlier work, the metastable ionized isomers do not reversibly interconvert. They do, however, have two dissociation channels, H2O and CO losses, for which common transition states are involved. Ionized maleic acid has one geometry‐specific dissociation, loss of CO2. Structures were assigned to all major fragment ions together with their heats of formation.
Investigation of non‐covalent ligand binding to the intact streptavidin tetramer by electrospray ionization mass spectrometry
Authors: Schwartz Brenda L. , Gale David C. , Smith Richard D. , Chilkoti Ashutosh , Stayton Patrick S.
Published: May 2005

The relative non‐covalent binding behavior of two small molecule ligands to the tetrameric protein streptavidin was investigated by electrospray ionization mass spectrometry (ESI‐MS). An extended m/z range quadrupole mass spectrometer was employed to observe the intact multimeric form of the protein and to probe the relative stabilities of the tetrameric protein‐ ligand complexes in the gas phase. Various protein:ligand molar ratio concentrations and incubation times were studied for the ligands biotin (Kd ≈ 10−15 M) and iminobiotin (Kd ≈ 10−7 M), in combination with the adjustment of variables in the ESI atmosphere‐vacuum interface region. Positive‐ion ESI‐MS of a 1:7 molar ratio streptvidin–biotin sample produced peaks corresponding to the intact tetrameric complex (16+ to 14+ charge states) with four ligands binding to the active from of the protein. Only the expected specific non‐covalent complexes of four ligand molecules binding to the protein tetramer were detected, consistent with known solution behavior and without the appearance of any random aggregation. However, under identical interface conditions, complete iminobiotin binding to the protein was not observed, even when higher ligand concentrations, longer complexation times and gentler interface conditions were employed. The thermally induced dissociation (TID) of the non‐covalent complexes was studied by applying more severe conditions in the ESI interface region. In addition, observation of an intact streptavidin–biotinylated oligonucleotide non‐covalent complex (17– to 14– tetrameric charge states) by negative‐ion ESI‐MS at m/z 4500–5000 is presented. The results show that the complexes observed in the mass spectrometer are representative of those that exist in solution, under the ESI conditions employed, and that the ability to observe such complexes is at least qualitatively related to stability in solution.
HD exchange kinetics of alcohols and protonated peptides: Effects of structure and proton affinity
Authors: Green M. Kirk , Gard Eric , Bregar Jennifer , Lebrilla Carlito B.
Published: May 2005

The kinetics of gas‐phase HD exchange reactions of a series of protonated amino acids and peptides with deuterium‐substituted alcohols (D2O, CH3OD, C2H5OD and 1‐C4H9OD) were studied in an external source Fourier transform mass spectrometer. The number of exchanges observed on the time‐scale of these experiments ranged from one to the total number of ‘labile’ substrate hydrogens, depending on the amino acid and the deuterating reagent. Exchange efficiencies, k/kADO, varied from <0.001 to 0.3. Within the series ROD, the reactivity increased with increasing size of the R group. For the amino acids with alkyl side‐chains, a roughly linear correlation of log(k/kADO) with proton affinity difference (ΔPA = PA of unprotonated substrate ‐ PA of reagent) was observed. The amino acids lysine and histidine and the dipeptides alanylglycine and diglycine showed higher reactivity and greater tendency for multiple exchange, with a weaker dependence on ΔPA. The ability of a peptide and an alcohol to exchange efficiently even when ΔPA is larger is attributed to the occurrence of exchange within a cyclic hydrogen‐bonded complex, in which the deuterating agent forms a bridge between the site of protonation and a basic site on the substrate.
Fragmentation mechanisms of protonated actinomycins and their use in structural determination of unknown analogues
Authors: Thomas Darren , Morris Michael , Curtis Jonathan M. , Boyd Robert K.
Published: May 2005

A combination of mass shifts arising from known structural variations of neutral precursors, and accurate mass measurements of key fragment tions, has led to a proposed systematization of the low‐energy fragmentation mechanisms for MH+ ions of actinomycins. These rationalizations are used in a predictive manner to interpret fragment ion spectra, of unknown impurities in actinomycin standards, in terms of structure. Both the strengths and limitations of this approach are emphasized. This work has uncovered actinomycin variants in which one of the threonine residues is substituted by serine, a structural variation which does not appear to have been reported previously.
Structural determination of 1,4‐naphthoquinones by mass spectrometry/mass spectrometry
Authors: Stensen Wenche G. , Jensen Einar
Published: May 2005

The fragmentation pathways of several substituted 1,4‐naphthoquinones have been studied by multi stage mass spectrometry. Methods for the recognition and identification of 1,4‐naphthoquinones and of substitution patterns on the naphthoquinone nucleus are outlined.
Trace determination of alkyl methylphosphonic acids in environmental and biological samples using gas chromatography/negative‐ion chemical ionization mass spectrometry and tandem mass spectrometry
Authors: Fredriksson Sten‐Åke , Hammarström Lars‐Gunnar , Henriksson Liselott , Lakso Hans‐Åke
Published: May 2005

Alkyl methylphosphonic acids (AMPA) are metabolites and primary hydrolysis products of the organophosphorus nerve agents listed in the Chemical Weapons Convention (CWC). Gas chromatography/negative‐ion chemical ionization mass spectrometry and tandem mass spectrometry (GC/NICI‐MS and GC/NICI‐MS/MS) were used for the determination of AMPA as their pentafluorobenzyl esters. Extremely high sensitivity was obtained and low attogram amounts could be detected by GC/NICI‐MS. Ion‐exchange chromatography was employed for selective isolation and enrichment of AMPA in serum, urine, water and soil samples. Collision‐induced dissociation (CID) of the single methylphosphonate anion peak from NICI of the pentafluorobenzyl ester produced fragment ions specific for the methylphosphonate structure, allowing positive identification of AMPA. CID conditions optimized for structure information and for sensitivity were investigated. The improved selectivity of GC/MS/MS allows the detection of femtogram amounts of AMPA in samples where chemical background inhibits detection by GC/MS.
Structures and stabilities of XCCY2+ dications (X, Y = O, S and NH), doubly charged isoelectronic analogues of cyanogen
Authors: Wong Ming Wah
Published: May 2005

Consistent with experimental observations, high‐level ab initio calculations, at the G2(MP2) level of theory, predict that the XCCY2+ (X, Y = O, S and NH) dications are remarkably stable species in the gas phase. OCCS2+, SCCS2+, HNCCO2+, HNCCS2+ and HNCCNH2+ are calculated to be thermodynamically stable species, whereas OCCO2+ is predicted to lie in a deep potential well, separated from exothermic CC cleavage by a large barrier. All the doubly charged species are calculated to have a linear skeleton. Despite the inherent strong Coulombic repulsion, these species are characterized by short CX or CY triple bonds. Vertical and adiabatic ionization energies of the XCCY+· monocations and the heats of formation of the resulting dications are reported. There are remarkable changes in the structures and stability ordering of isomers on going from the XCCY neutrals to the XCCY+· monocations and to the XCCY2+ dications. The rationalization of these results is discussed.
Quantification of the anti‐HIV drug saquinavir by high‐speed on‐line high‐performance liquid chromatography/tandem mass spectrometry
Authors: Knebel N. G. , Sharp S. R. , Madigan M. J.
Published: May 2005

A method is described for the fast routine determination of the anti‐HIV drug saquinavir and its pentadeuterated analogue [2H5] saquinavir in the plasma of healthy volunteers. The method is based on high‐performance liquid chromatography (HPLC)/atmospheric pressure positive‐ion chemical ionization (APCI) mass spectrometry, with a stable labelled form of saquinavir (13C6–2H3–15N) as internal standard. Automated solid‐phase extraction in combination with short‐column HPLC and multiple reaction monitoring is employed for high selectivity and sensitivity, and this also permits rapid quantification (the run time per sample is 1.5 min) over the range of 0.4–200 ng ml−1 with excellent accuracy and precision. Up to 200 samples per analyst per day can be analysed. This assay methodology illustrates the versatility of APCI tandem mass spectrometry, in conjunction with high‐speed HPLC, for the fast routine quantification of drugs in the nanograms per millilitre range, which is essential for clinical pharmacokinetic studies.
Characterization of endogenous DNA adducts by liquid chromatography/electrospray ionization tandem mass spectrometry
Authors: Chaudhary Ajai K. , Nokubo Munetaka , Oglesby Thomas D. , Marnett Lawrence J. , Blair Ian A.
Published: May 2005

Endogenous carcinogens arising from normal metabolism are known to cause modifications to DNA by reacting with bases to form adducts. Malondialdehyde is a well characterized endogenous carcinogen that forms an adduct with 2′‐deoxyguanosine. This adduct has been detected in rat and human liver DNA by gas chromatography/electron capture negative‐ion chemical ionization mass spectrometry. A method has been developed based on liquid chromatography/electrospray ionization tandem mass spectrometry for the characterization of endogenous DNA adducts. Using this method, it was unequivocally established that the malondialdehyde adduct of 2′‐deoxyguanosine was a constituent of human liver DNA. The methodology that has been developed should be applicable to the characterization of other endogenous DNA adducts. There are few structural or biological data available to assess the importance of endogenous DNA adducts as premutagenic lesions responsible for the development of cancer. The availability of methodology based on liquid chromatography/electrospray ionization tandem mass spectrometry for the characterization of DNA adducts should greatly facilitate future studies in this area.
Electron affinities of polycyclic aromatic hydrocarbons determined by the kinetic method
Authors: Chen Guodong , Cooks R. Graham
Published: May 2005

The kinetic method has been applied in the determination of electron affinities (EA) of polycyclic aromatic hydrocarbons (PAHs) using electron attachment desorption chemical ionization mass spectrometry (DCI‐MS) and triple quadrupole tandem mass spectrometry. Electron‐bound dimers of PAHs (viz. solvated radical anions) are generated in the ion source and they fragment competitively upon collisional activation to yield the intact monomeric molecular radical anions. The ratio of the abundances of these two ions reflects the difference in electron affinities of the PAHs. Relative electron affinities are ordered as phenanthrene < perylene < 1,2‐benzanthracene < benzo [ghi] perylene < anthracene < pyrene < fluoranthene < biphenylene on the basis of multiple pairwise measurements. On the assumption that the effective temperature of the electron‐bound dimers is constant, under fixed desorption conditions, and using phenanthrene (EA = 0.307 eV), anthracene (EA = 0.556 eV), pyrene (EA = 0.591 eV) and fluoranthene (EA = 0.63 eV) as reference compounds, the electron affinities of several PAHs are estimated as perylene (0.35 eV), 1,2‐benzanthracene (0.39 eV), benzo [ghi] perylene (0.42 eV) and biphenylene (0.89 eV). The calculated effective temperature using the known EAs of the reference compounds, phenanthrene, anthracene, pyrene and fluoranthene, is 1251 K. The high effective temperature in the electron‐bound dimer is ascribed to both the weak binding in the electron‐bound dimer and to the choice of ionization conditions. The same methodology was applied to estimate the electron affinities of substituted PAHs. For alkyl‐substituted PAHs, e.g. 1‐methylanthracene, the estimated electron affinity (0.55 ± 0.10 eV) is consistent with electron transfer equilibrium studies. However, for halogenated PAHs, the ratio of fragment ion abundances does not correlate with the known electron affinity difference when a PAH and a halogenated PAH comprise the electron‐bound dimer. This is suggested to be due to differences in the structures of the cluster ions generated upon halogen substitution. The expected affinity results are obtained when the electron‐bound dimer is comprised of two halogenated PAHs. Estimated electron affinity values for 1‐bromopyrene (0.72 ± 0.10 eV) and 9‐bromoanthracene (0.61 ± 0.10 eV) are slightly higher than the electron affinities of pyrene and anthracene, respectively.
Effect on conformation on proton affinities of stereoisomeric ethers
Authors: Denekamp C. , Etinger A. , Fokkens R. H. , Khaselev N. , Mandelbaum A. , Nibbering N. M. M.
Published: May 2005

The proton affinity (PA) of cis‐4‐tert‐butylcyclohexyl methyl either with an axial methoxy group is higher by ∼0.1 kcal mol−1 (1 kcal = 4.184 kJ) than the trans isomer with the equatorial ether group. The gas‐phase basicity shows a similar small difference of 0.1 kcal mol−1 between the two stereoisomeric ethers. A greater difference in PA has been observed between the stereoisomeric 4‐phenylcyclohexyl methyl and ethyl ethers (1.0 and 1.2 kcal mol−1, respectively), in favour of the cis isomers with the equatorial ether groups. The latter result is explained by the internal hydrogen bond with the π‐system of the phenyl ring.
Reactions of protonated acetic acid clusters (CH3COOH)nH+ (n = 1–3)
Authors: Feng Wan Yong , Lifshitz Chava
Published: May 2005

Reactions of (CH3COOH)nH+ (n = 1–3) with a series of base molecules B were studied using a selected ion flow tube. All the reactions observed proceed at near gas kinetic collision rates for bases having higher proton affinities than acetic acid. Different reaction channels are observed with increasing proton affinity of the neutral: association and proton transfer for the proton‐bound monomer; association, ligand switching and proton transfer for the dimer; association, ligand switching, switching with solvent evaporation and proton transfer for the trimer. A thermochemical comparison of the appearance enthalpy and free energy for proton transfer from (CH3COOH)3H+ and (C2H5OH)3H+ established that both sets of reactions take place by forming BH+ with evaporation of three monomeric units (of acetic acid or ethanol, respectively) rather than evaporation of neutral dimers. Proton transfer from (CH3COOH)2H+ is fast provided that the reaction is exothermic; proton transfer from (CH3COOH)3H+ is fast even if the reaction is endothermic (but exergonic).
Identification of quaternary ammonium and tertiary sulfonium compounds by plasma desorption mass spectrometry
Authors: Bonham Connie C. , Wood Karl V. , Yang Wen‐Ju , Nadolska‐Orczyk Anna , Samaras Yiannis , Gage Douglas A. , Poupart Julie , Burnet Michael , Hanson Andrew D. , Rhodes David
Published: May 2005

A rapid and sensitive method for the identification of quaternary ammonium and tertiary sulfonium compounds is described. The method utilizes plasma desorption mass spectrometry (PDMS) in which a 252Cf ionizing source produces fission fragments which interact with the sample to yield ions which are then analyzed by a time‐of‐flight mass spectrometer. The method was applied to analyses of authentic standards and to the identification of quaternary ammonium and tertiary sulfonium compounds in higher plant leaf extracts purifed by ion‐exchange chromatography. Plant species from 14 different families were tested, including species which are known glycinebetaine, β‐alaninebetaine, prolinebetaine or β‐dimethylsulfoniopropionate accumulators. PDMS results confirmed and extended the known taxonomic distributions of these compounds. Glycinebetaine was found in one species Krameria parvifolia from a family (Krameriaceae) not previously known to accumulate this compound. Pipecolatebetaine was identified in Achillea filipendulina (Asteraceae). The occurrence of prolinebetaine and hydroxyprolinebetaine(s) was confirmed in three species (Lamium maculatum, Stachys byzantina and Phlomis fruticosa) of the tribe Lamieae of the subfamily Lamioideae in the family Lamiaceae, but not in a fourth member of this tribe (Physostegia virginiana). The last species accumulated only trigonelline. The PDMS method was also used to identify trigonelline‐deficient Zea mays lines.
Cycloreversal reaction and ortho interactions in 2‐aryl‐4H‐3, 1‐benzoxazin‐4‐ones on electron impact
Authors: Ramana D. V. , Kantharaj E.
Published: May 2005

A cycloreversal reaction, leading to aroyl cations, is the major process in 2‐aryl‐4H‐3,1‐benzoxazin‐4‐ones under electron impact conditions. The ortho interaction of the methoxy and the nitro groups in the 2‐phenyl moieties in these compounds present the most abundant ions at m/z 119 and 134, respectively, in their mass spectra as a result of the transfer of a hydrogen atom from the former and an oxygen atom from the latter to the imine nitrogen of the heterocycle. The ion structures and the mechanisms for the proposed fragmentations are based on high‐resolution data, B/E and B2/E linked‐scan spectra, collision‐activated decomposition–B‐/E linked‐scan spectra and deuterium labelling.
Special feature: Historical. Collision‐induced dissociation: Readings and commentary
Authors: Cooks R. Graham
Published: May 2005

Collision‐induced dissociation (CID), also known as collision‐activated dissociation (CAD), is now central to the practice of mass spectrometry. The story of its discovery, fundamental basis, and its development as a technique applicable to different types of instruments has evolved over many decades. In this paper, these topics are explored by reference to and commentary on particular texts, chosen to represent milestones in the development of CID over the period 1910–1970.
Magnitude‐mode multiple‐derivative spectra for resolution enhancement without loss in signal‐to‐noise ratio in Fourier transform spectroscopy
Authors: Kim Hyun Sik , Marshall Alan G.
Published: May 2005

An nth‐derivative Fourier transform complex spectrum, dnF(ω)/dωn, may be generated by multiplying at time‐domain signal by (−it)n before Fourier transformation. The resolving power of the magnitude‐mode nth‐derivative spectrum, |dnF(ω)/dωn|, increases monotonically with increasing derivative order, but with concomitant decrease in signal‐to‐noise ratio. However, application of time‐domain exponential windowing can restore the signal‐to‐noise ratio. The combined derivatization–windowing process yields a magnitude‐mode nth‐derivative Fourier transform spectrum with significantly enhanced resolution near the peak base without loss in signal‐to‐noise ratio. A theoretical analysis of the trade‐off between resolving power and signal‐to‐noise ratio for magnitude‐mode nth‐derivative Fourier transform spectra as a function of time‐domain signal truncation, time‐domain windowing (exponential) and derivative order is presented. The method is demonstrated experimentally for Fourier transform ion cyclotron resonance mass spectra.
Mass discrimination in matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry: A study using cross‐linked oligomeric complexes
Authors: Farmer Terry B. , Caprioli Richard M.
Published: May 2005

The determination of the mass discrimination effect of matrix‐assisted laser desorption ionization mass spectrometry (MALDI MS) over a wide m/z range was made by determining the relative amounts of prepurified protein monomer and dimer species present in reconstituted mixtures. Protein complexes were covalently cross‐linked with glutaraldehyde and monomeric and dimeric species were separated by gel filtration chromatography. Individual protein species were recombined in specific ratios and analyzed by both MALDI MS and sodium dodecyl sulfate polyacrylamide gel electrophoresis. The contributions of the peak areas of the doubly charged ions and singlycharged dimeric ions generated during the MALDI MS analyses relative to that of the singly‐charged [M + H]+ species were measured. The calculation of mass discrimination for two different MALDI time‐of‐flight instruments showed the loss of a factor of ∼2.6 in relative peak area as the m/z value doubled over the m/z range 30 000–145 000. An overall correction factor for mass discrimination is given which includes effects associated with sample preparation, sample desorption/ion formation, ion transmission and ion detection.
Two‐dimensional mass spectra of 2‐phenylethylamines
Authors: Cardoso Ana M. , Correia A. J. Ferrer
Published: May 2005

The two‐dimensional mass spectra (metastable mapping) of ten biogenic amines derived from the amino acid 2‐phenylalanine are described. This technique permitted the identification of almost all the fragmentations of singly and doubly charged positive ions formed by electron impact and decomposing in the different parts of a reverse‐geometry mass spectrometer. The results obtained are discussed in order to establish the main fragmentation pathways common to all the amines belonging to the general class of 2‐phenylethylamines and to identify the fragmentations characteristic of each amine.
Simultaneous determination of concentrations and stable isotope enrichments of α‐ketoisocaproic acid, leucine, phenylalanine and tyrosine in blood plasma by gas chromatography/negative ion mass spectrometry
Authors: Kulik W. , van Toledo‐Eppinga L. , Kok R. M. , Guérand W. S. , Lafeber H. N.
Published: May 2005

A simple procedure for the extraction and derivatization of α‐amino acids and α‐keto acids from human plasma is described. This stable isotope dilution method permits the quantification of isotopic enrichment and concentrations of several α‐keto and α‐amino acids simultaneously. The derivatization process results in methylformated, pentafluorobenzylated α‐amino acids and pentafluorobenzylated α‐keto acids. The derivatives proved to be very stable when stored at 5°C. Under electron capture chemical ionization (ECCI) conditions the derivatized amino acid produces abundant [M – PFB]− or [M – PFB – CH3OH]− anions; the α‐keto acid gives abundant [M – PFB]− anions. The method was applied to the analyses of 100 μl plasma samples in studies on protein metabolism. For the determination of concentrations [α‐ketoisocaproic acid (α‐KIC), Leu, Phe and Tyr] and enrichments ([1‐13C]‐α‐KIC, [1‐13C]‐Leu, D5‐Phe, D2‐Tyr, D4‐Tyr), resulting from administered tracers, the corresponding [M – PFB]− or [M – PFB – CH3OH]− anions were monitored. Higher labelled analogues were used as internal standards. The overall sensitivity was sufficient to study isotopic enrichments in the range 0.2–10 at.% excess.
Site of gas‐phase methylation of alkyl phenyl ketones
Authors: Cheung Mary , Harrison Alex G.
Published: May 2005

The CH adducts of benzaldehyde, acetophenone, propiophenone and butyrophenone were prepared using CH3FCH4 and CH3ClCH4 mixtures under chemical ionization conditions and the unimolecular and collision‐induced fragmentation reactions of their adduct ions were studied. For comparison, the fragmentation reactions of the protonated p‐methylphenyl alkyl ketones were studied as models of the ring‐methylated species and the fragmentation reactions of [C6H5C(R)OCH3]+, produced by electron impact ionization of the appropriate methyl ether, were studied as models of the O‐methylated species. From these comparisons it is concluded that methyl cation addition occurs predominantly at the carbonyl oxygen under our experimental conditions. However, for methyl‐cationated acetophenone there is extensive migration of the methyl group from the oxygen to the ring prior to fragmentation of the adduct.
Metastable and collision‐induced fragmentation of selected C3H6S+· isomers; evidence for extensive isomerization
Authors: Hop Cornelis E. C. A.
Published: May 2005

The metastable ion (MI) and collision‐induced dissociation (CID) mass spectra of five C3H6S+· isomers were examined. The MI mass spectra were virtually identical, which suggests that C3H6S+· ions having a substantial amount of internal energy can freely interconvert and isomerize into a common structure prior to fragmentation. However, the CID mass spectra are distinctly different and the differences can be related to the structure of the C3H6S+· isomers. It was even possible to distinguish the distonic ion H2CCH2SCH2+· from its conventional counterpart magnified image. The smaller amount of internal energy of the ions probed in CID experiments obviously limits isomerization.
Determination of both linkage position and anomeric configuration in underivatized glucopyranosyl disaccharides by electrospray mass spectrometry
Authors: Mulroney Brad , Traeger John C. , Stone Bruce A.
Published: May 2005

Negative‐ion electrospray mass spectrometry was used to determine directly both glycosidic linkage position and anomeric configuration in the complete glucopyranosyl disaccharide series without the need for derivatization or tandem mass analysis. A series of empirical criteria were developed which first differentiate between the linkage positions and then the anomeric configurations using selected diagnostic peaks and their relative intensities. The use of standard mass spectral library searching methods for structural analysis was also investigated.
Formation by fast atom bombardment of molecular radical cations by electron donor–acceptor complexes from tosylated amino acid esters
Authors: Athanassopoulos Constantions , Papaioannou Dionissios , Napoli Anna , Siciliano Carlo , Sindona Giovanni
Published: May 2005

N‐Alkyl‐N‐tosyl amino acid esters were ionized by fast atom bombardment (FAB) in a nitrobenzyl alcohol matrix through oxidative processes leading to molecular radical cations (M+·). The addition to the matrix of Cu11 salts induces the ionization through proton attachment whereby [M + H]+ are exclusively displayed by the positive‐ion FAB spectra. The formation of electron donor–acceptor complexes between the analytes and the matrix lowers the critical energy for the ionization by one‐electron removal from the substrates.
Analysis of the chemical defence system in an insect larva by tandem mass spectrometry
Authors: Gfeller Hans , Schlunegger Urs P. , Schaffner Urs , Boevé Jean‐Luc , Ujvary Istvan
Published: May 2005

Larvae of the sawfly Rhadinoceraea nodicornis Konow (Hymenoptera, Tenthredinidae) living on the plant Veratrum album L. (Liliales, Melanthiaceae) are efficiently protected against ants and spiders. Moreover, when their haemolymph was offered in a sugar solution, ants were still deterred. The chemical defence system of these larvae was investigated and the structures of the biologically active compounds determined by tandem mass spectrometry. Plant‐derived alkaloids both in original and metabolized form were found in the larval haemolymph.
Identification and determination of cystathionine sulfoxide and NAc‐cystathionine sulfoxide in the urine of a patient with cystathioninuria using liquid chromatography/atmospheric pressure chemical ionization mass spectrometry
Authors: Zhang Jianying , Masuoka Noriyoshi , Ubuka Toshihiko , Kodama Hiroyuki
Published: May 2005

Novel cystathionine metabolities, cystathionine sulfoxide and NAc‐cystathionine sulfoxide, were identified in the urine of a patient with cystathioninuria using liquid chromatography/mass spectrometry with an atmospheric pressure chemical ionization interface system. NAc‐cystathionine sulfoxide was discovered as a new metabolite of cystathionine in the urine of a cystathioninuric patient. The concentrations of cystathionine sulfoxide and NAc‐cystathionine sulfoxide in this urine were also determined for the first time using this method, and were 28.69 ± 0.44 and 10.51 ± 0.49 mg g−1 creatinine, respectively. Neither compound was detected in the urine of healthy subjects.
Matrix‐assisted laser desorption/ionization mass spectrometry of sphingo‐ and glycosphingo‐lipids
Authors: Harvey David J.
Published: May 2005

Sphingo‐ and glycosphingo‐lipids were examined by matrix‐assisted laser desorption/ionization mass spectrometry on a time‐of‐flight (TOF) and a magnetic sector mass spectrometer with 2,5‐dihydroxybenzoic acid (2,5‐DHB), sinapinic acid, α‐cyano‐4‐hydroxycinnamic acid, 2‐(4‐hydroxyphenylazo)benzoic acid (HABA) and esculetin as the matrices. Strong signals were produced by all lipids tested, with many of the compounds producing structurally useful fragment ions. Neutral glycosphingolipids gave the best signals in the positive‐ion mode with 2,5‐DHB, α‐cyano‐4‐hydroxycinnamic acid and esculetin. When 2,5‐DHB was used as the matrix, glycosphingolipids that did not contain HexNAc residues tended to fragment between the sugar and ceramide moieties to give ions revealing the saccharide and lipid contents. Other matrices tended not to induce this fragmentation but, instead, produced ions resulting from loss of that acylamide from the ceramide moiety. These ions revealed the distribution of carbon atoms between the acyl and sphingosine chains. Fragmentation of the oligosaccharide chain of glycolipids that did contain HexNAc groups tended to be more random than that seen when HexNAc was absent and provided considerable sequence information. The acidic gangliosides produced broad, unresolved fragment ion peaks on the TOF spectrometer. Fragmentation was the result of both decarboxylation and loss of sialic acids. On the magnetic sector instrument, these fragment ions were sharp and well resolved. Additional fragment ions resulting from glycosidic cleavages provided information about the sequence of sugars in the oligosaccharide chain. Negative‐ion signals ([M − H])− from the acidic glycosphingolipids were generally better defined than those in the positive‐ion spectra as the result of a reduction in alkali metal adduct and salt formation.
GC/MS analysis of [2H5]phenylalanine at very low enrichment: Measurement of protein synthesis in health and disease
Authors: Slater Christine , Preston Tom , McMillan Donald C. , Falconer J. Stuart , Fearon Kenneth C. H.
Published: May 2005

A gas chromatographic/mass spectrometric (GC/MS) method has been developed for the precise and accurate analysis of high enrichment (1–10 mol.% excess) and very low enrichment (0.005–0.12 mol.% excess) 2H5‐labelled phenylalanine. Tracer enrichment in free phenylalanine was measured by GC/electron impact MS analysis of the tert‐butyldimethylsilyl (TBDMS) derivative. The measurement of very low tracer enrichment, typical of that found in protein hydrolysates, was accomplished by careful control of sample yield during preparation and analysis of the TBDMS derivative of purified β‐phenylethylamine, produced by enzymatic decarboxylation and solvent extraction. The new method was illustrated by measurement of albumin synthesis in healthy patients using a rapid protocol which showed good patient acceptability and was straightforward to manage in the clinical setting. The mean (SEM) albumin fractional synthetic rate was 9.54% (0.81%) per day, in agreement with previous studies that used more complex clinical protocols and analytical procedures. Use of the same derivative for analysis of amino acid precursor and protein samples facilitated consecutive analysis on the same instrument without interruption, permitting rapid feedback of results to the clinician and the possibility of using the method in intervention studies. The method should prove useful in the study of the synthetic rate of other proteins and mixed tissue protein, which will help our understanding and management of protein metabolism in health and disease. The possibility of extending the use of multiple‐atom tracers combined with GC/MS analysis to other substrate metabolism studies was identified.
‘Underflow’ introduction system for solid and liquid samples in bench‐top gas chromatographic/mass spectrometric systems
Authors: Favretto Donata , Cecchinato Francesco , Traldi Pietro , March Raymond E.
Published: May 2005

A simple, inexpensive inlet system was developed for the introduction of liquid and solid samples, to be employed in commercial gas chromatographic/mass spectrometric instruments, and not requiring sample injection through the chromatographic column. The system does not need any modifications of the ion source housing and pumping system and is based on admitting the sample vapour as an underflow to the normal helium flow through the chromatographic column at a location near the transfer line.
Special feature: Perspective. Mass spectrometric detection of carcinogen adducts
Authors: Farmer P. B. , Sweetman G. M. A.
Published: May 2005

Genotoxic carcinogens interact with nucleic acids and proteins to yield covalently bound products (adducts), the quantitative determination of which has been proposed as a biomonitor of human exposure to carcinogens. Mass spectrometry is playing a leading role both in the structural characterisation and in the quantitative determination of these carcinogen adducts. In particular electrospray ionisation and matrix assisted laser desorption ionisation are being increasingly used in nucleotide and protein adduct detection and in sequencing of carcinogen‐modified oligonucleotides and peptides. Quantitative determination of carcinogen‐modified nucleic acid bases and protein amino acids is generally carried out by GC/MS or GC/MS/MS, the highest sensitivity being achieved using negative ion chemical ionisation. These techniques are now being applied to samples from humans exposed to carcinogens from environmental, medicinal and occupational sources.
Identification of amperozide metabolites in urine from rats, rabbits, dogs and man by Frit‐FAB LC/MS using deuterated solvents to gain additional structural information
Authors: Edlund P. O.
Published: May 2005

A general procedure for screening of amperozide, N‐ethyl‐4‐[4,4‐bis(p‐fluorophenylbutyl)]‐1‐piperazine carboxamide, labelled with 3H and 14C was developed. Urine extracts were first fractionated by preparative reversedphase chromatography with an acetonitrile gradient elution. The collected fractions were finally analysed using a methanol gradient on packed capillary LC columns with an internal diameter of 0.32 or 0.5 mm connected to the Frit‐FAB probe of a Jeol SX‐102 mass spectrometer for structural analysis. A micro‐gradient system dedicated for the use of deuterated solvents was constructed from two six‐port switching valves to reduce the consumption of the eluents. The number of hydrogens bound to heteroatoms (OH, NH) was determined by comparing the spectra recorded from mobile phases using water and deuterium oxide. The mass spectra recorded during elution with deuterated solvents was also useful for the interpretation of the fragmentation pattern of standard compounds and unknown metabolites. The technique proved especially useful to differentiate between hydroxylation and N‐oxidation which gave the same increase in molecular mass by 16 u but a difference in the number of exchangeable protons. Metabolites formed by oxidative N‐dealkylation of amperozide either at the basic nitrogen or at the N‐ethylcarboxamide nitrogen were identified. Additional metabolites derived from deethylated amperozide inovlving N‐oxidation of the basic nitrogen of the piperazine ring and/or hydroxylation of the piperazine ring were identified. Metabolites formed by oxidative N‐dealkylation and opening of the piperazine ring were also identified.
Detection of testosterone esters in human plasma
Authors: de la Torre Xavier , Segura Jordi , Polettini Aldo , Montagna Maria
Published: May 2005

The detection of testosterone misuse in sports is currently based on the urinary testosterone to epitestosterone ratio, although in some rare instances physiological or pathological conditions could compromise the application of this general criterion. The detection in the body of traces of the unchanged testosterone esters really ingested would offer unequivocal confirmation of testosterone administration. In this work, the detectability of testosterone esters in humans was studied. Liquid–liquid extraction of human blood plasma and appropriate derivatization of nine testosterone esters are described. Different acyl (trifluoroacetyl, pentafluoropropionyl and heptafluorobutyryl) and trimethylsilyl derivatives were studied. The trimethylsilyl derivatives appear to be the best for screenign purposes based on the characteristics of their mass spectra, with abundant molecular ions in the high‐mass range. They also offered good conditions for tandem mass spectrometric analysis, needed to achieve the required sensitivity after oral administration of the drugs. The method was successful in the detection and determination of intramuscularly administered testosterone propionate and testosterone enanthate and orally ingested testosterone undecanoate.
Fast atom bombardment mass spectrometry of phospholipids in human cerebrospinal fluid
Authors: Mollova Nevena N. , Moore Ida Marie (Ki) , Hutter John , Schram Karl H.
Published: May 2005

Lipid extracts of cerebrospinal fluid (CSF) collected from children with leukemia were separated on normal‐phase high‐performance liquid chromatography (HPLC) and analyzed by fast atom bombardment mass spectrometry (FABMS) and tandem FABMS/MS. CSF samples from 13 children with leukemia receiving chemotherapy and radiation treatment were analyzed. Analysis of the results permits the identification of phosphatidylcholine (PC), sphingomyelin (SM), diacylglycerol (DAG) and lysophosphatidylcholine (LPC) molecular species. The following changes in the CSF phospholipid composition during treatment with chemotherapy were identified: (i) presence of DAGs and LPCs and (ii) increase in SM relative to PC. A predominance of the C18:1 SM was observed during radiation treatment. To our knowledge, this is the first report of the application of HPLC and FABMS for the analysis of human CSF. The possibility of using FABMS and FABMS/MS for the direct analysis of the total CSF lipid extracts in cancer patients is demonstrated.