bluuebunny/crossref_metadata_2025 huggingface dataset:
A method for the structural determination of cannabichromene metabolites by mass spectrometry
Authors: Harvey D. J. , Brown N. K.
Published: May 2005

Ready identification of hydroxy metabolites of cannabichromene (CBC) by mass spectrometry of their trimethylsilyl derivatives is prevented by the dominant fragmentation to give a substituted chromenyl ion; this suppresses ions diagnostic of the position of metabolic hydroxylation. To overcome this difficulty, metabolites were hydrogenated over a rhodium/alumina catalyst to reduce the double bond responsible for chromenyl ion formation and to redirect the fragmentation to the site of metabolic attack. This resulted in the production of abundant diagnostic fragment ions enabling all monohydroxy‐CBCs to be readily identified.
Ion cyclotron resonance signal‐detection at multiples of the cyclotron frequency
Authors: Nikolaev E. N. , Gorshkov M. V. , Mordehai A. V. , Talrose V. L.
Published: May 2005

A Fourier‐transform mass spectrometric technique for detecting ion cyclotron resonance signals at multiple cyclotron frequencies is proposed and initial experimental results are presented. The technique is readily adapted to existing instruments.
Electrospray ionization on a high‐performance magnetic‐sector mass spectrometer
Authors: Meng Chin‐Kai , McEwen Charles N. , Larsen Barbara S.
Published: May 2005

The feasibility of interfacing an electrospray ion source to a high‐performance magnetic‐sector mass spectrometer is demonstrated. Spectra of peptides and small proteins are obtained with good sensitivity, resolution and mass accuracy. The advantages of using a high‐performance mass spectrometer in conjunction with electrospray ionization are discussed.
An MNDO study of substituent effects on the electronic structure and geometry in the ionization of CH3R compounds (R = H, F, Cl, OH, SH, NH2)
Authors: Hrušá Jan , Tkaczyk Martin
Published: May 2005

MNDO calculations on compounds CH3R (where R  H, F, Cl, OH, SH, NH2) enable qualitative correlations to be made between the changes in bond length during ionization and the observed fragmentation of the ion formed. The relatively simple, semi‐empirical MNDO method gives data adequate for the calculation of the geometries and energies involved.
Ion‐spray mass spectrometry of marine toxins II. Analysis of diarrhetic shellfish toxins in plankton by liquid chromatography/mass spectrometry
Authors: Pleasance S. , Quilliam M. A. , de Freitas A. S. W. , Marr J. C. , Cembella A. D.
Published: May 2005

A combined liquid chromatography/mass spectrometry (LC/MS) method using ion‐spray ionization is described for the sensitive determination of okadaic acid and dinophysistoxin‐1, the principal toxins implicated in cases of diarrhetic shellfish poisoning. The method is used to confirm the presence of okadaic acid in a culture of the dinoflagellate species Prorocentrum concavum and in natural populations of dinoflagellates from eastern Canadian waters. Several analogues of the toxin have also been detected. Quantitative results are comparable to those obtained by high performance liquid chromatography with fluorescence detection. With slight modifications, the LC/MS method is also used to analyse the fluorescent anthrylmethyl ester of okadaic acid. Preliminary tandem mass spectrometric results, obtained using fast‐atom bombardment ionization, are presented for okadaic acid.
Quantitative analysis of 1‐stearoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphoserine by negative‐ion fast‐atom bombardment mass spectrometry
Authors: Chen Su , Kirschner Günther , Benefenati Emilio
Published: May 2005

Negative‐ion fast‐atom bombardment mass spectrometry was evaluated as a means for quantitative analysis of individual molecular species of glycerophosphatidylserine (GPS). With 200 ng of 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphoserine (GPS di 16:0) as an internal standard, the calibration curve for 1‐stearoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphoserine (GPS 18:0–18:1) was linear over a range of 50–1000 ng (signal‐to‐noise ratio >4), with a correlation coefficient of 0.998. When the curve was derived from a mixture of GPS molecular species, only a slight variation in the ion intensity ratio of GPS 18:0–18:1 to GPS di 16:0 occurred. The method provides the possibility of quantifying GPS 18:0–18:1 among GPS species in the low nanogram range.
Sequential multiple‐scan monitoring using an ion‐trap mass spectrometer
Authors: Creaser C. S. , Mitchell D. S. , O'Neill K. E. , Trier K. J.
Published: May 2005

Novel scan routines, termed ‘multiple‐scan monitoring’ cycles, have been developed for the rapid sequential acquisition of data from two or more scan types using ion‐trap mass spectrometry. These cycles allow data to be acquired from multiple‐scan functions with a cycle time compatible with combined chromatography/mass spectrometry and other sample introduction methods. Multiple‐scan monitoring is illustrated for the measurement of the components of a test mixture, and for the determination of sulphamethazine and tetrachlorodibenzo‐p‐dioxin.
Thermospray ionization with repeller‐induced collisionally activated dissociation of dyes
Authors: Yinon Jehuda , Jones Tammy L. , Betowski Leon D.
Published: May 2005

Thermospray ionization with repeller‐induced collisionally activated dissociation (repeller‐CAD) has been used to acquire mass spectra of a series of dyes. These were obtained by applying a voltage of 400 V on the wire repeller. The mass spectra contained a large number of fragment ions which were useful for structural elucidation. Some of these fragment ions were found to be similar to those obtained by thermospray tandem mass spectrometry with CAD and some of them were similar to those obtained by electron ionization using a particle beam liquid chromatograph/mass spectrometry interface. The results indicate that more than one mechanism is involved in the fragmentation process.
Effect of different target gases on low‐energy collision‐activated dissociation of peptides
Authors: Naylor Stephen , Lamb John H.
Published: May 2005

Experimental variables affecting the daughter‐ion spectra of a series of protonated peptides [MH]+, produced by fast‐atom bombardment ionization, using a low energy (0–450 eV) quadruple collision cell are investigated. The parameters studied include target gas pressure, collision energy, cross‐sectional area and acidity of the target gas. The results show that low‐mass immonium ions are preferentially formed both at high collision energies (> 200 eV) and at target gas pressures > 10−6 mBar (where multiple collisions occur in the gas cell). Positive fragment ion abundance is maximized when acidic gases are used as the target gases, and this is rationalized on the basis of a proton‐transfer reaction from the target gas to the amide nitrogen of the peptide bond promoting fragmentation.
Do deprotonated semicarbazones undergo the negative‐ion Beckmann rearrangement in the gas phase?
Authors: Adams Gregory W. , Bowie John H.
Published: May 2005

Most deprotonated semicarbazones do not undergo the negative‐ion Beckmann rearrangement: instead, simple radical and/or neutral loss is noted, e.g., Me2CNNHCON̄H→[Me2CNNH−(OCNH)]→OCN−+Me2CNNH2. However, dimethyl derivatives do undergo minor fragmentation possibly indicative of a Beckmann rearrangement, e.g., .
The unusual collision‐induced dissociations of deprotonated cyclopentanones
Authors: Alexander Margaret J. , Raftery Mark J. , Bowie John H. , Hayes Roger N.
Published: May 2005

The major collision‐induced dissociations of deprotonated cyclopentanone involve losses of H2, C2H5 and CH2O. Mechanisms for these processes are proposed.
Electron ionization mass spectra of some cyclohexane fused 2‐N‐phenyliminoperhydro‐1,3‐oxazines and related thiazines
Authors: Pihlaja Kalevi , Lötjönen Lenita , Fülöp Ferenc , Bernáth Gábor , Vainiotalo Pirjo
Published: May 2005

The 70 eV electron ionization mass spectra of six cyclohexane fused 2‐N‐phenyliminoperhydro‐1,3‐oxazines and six related thiazines were recorded and their fragmentation patterns were studied by metastable‐ion analysis and exact mass measurement. All the compounds examined lost a hydrogen atom from their molecular ion in a process best described as intramolecular cyclization. The most typical fragmentations were the loss of various alkyl radicals from the M+· or [MH]+ ions with the simultaneous migration of one or more hydrogen atoms from the carbocyclic part to the heterocyclic part of the molecule. N‐Substitution clearly affected the type and extent of different reactions. In general, the fragmentation patterns of the thiazine derivatives were more complicated than those of the related oxazines. In all cases studied, the cis‐ and trans‐fused isomers gave rise to so similar spectra that their adequate differentiation was not possible.
Mass spectrometric investigation of diphenylacetylene (tolane)
Authors: Srzić Dunja , Žinić Mladen , Meić Zlatko
Published: May 2005

The electron‐ionization induced fragmentation of diphenylacetylene and its d1, d2, d5 and d10 analogues has been studied by mass spectrometry. The main fragment ions found in the mass spectrum of diphenylacetylene are due to the loss of two hydrogen radicals in a stepwise process and expulsion of C2H2 from the molecular ion in parallel fragmentation pathways producing the fragment ions at m/z 176 and m/z 152, respectively, the latter having possibly a biphenylene radical cation structure. Knowing the actual composition of deuterated derivatives, and the fragmentation pattern of diphenylacetylene, the distribution of the label in these ions was calculated under the assumption that this distribution is statistical. The final results were compared with the experimentally observed spectra of deuterated compounds. This comparison favours the assumption of hydrogen randomization prior to m/z 176 and m/z 152 formation. In contrast to the loss of hydrogen radicals and of C2H2, the formation of m/z 139, 126 and 102 does not involve any major hydrogen scrambling between the phenyl rings.
Collisionally‐activated dissociation of methane molecular ion. Analysis of a mass‐analysed ion kinetic energy peak shape
Authors: Kim Byung Joo , Kim Myung Soo
Published: May 2005

Collisionally‐activated dissociation (CAD) of methane molecular ion to methyl ion is studied in the kiloelectronvolt collision energy region by mass‐analysed ion kinetic energy (MIKE) spectrometry. The CAD‐MIKE peak shape was deconvoluted using the algorithm developed previously. The kinetic energy release distribution evaluated from the deconvoluted peak shape exhibits a bimodal feature. This is attributed to the participation of two different mechanisms for collisional activation, leading to electronic and vibrational excitations, respectively.
Time‐of‐flight mass spectrometry of nucleic acids by laser ablation and ionization from a frozen aqueous matrix
Authors: Nelson Randall W. , Thomas Robert M. , Williams Peter
Published: May 2005

Positive‐ion time‐of‐flight mass spectra of sodium salts of oligodeoxyribonucleic acids (DNA), and a protein, lysozyme, have been obtained using pulsed‐laser ablation and ionization of frozen aqueous solutions from a cooled copper substrate. The efficiency of positive‐ion formation was found to increase when the ablating laser was tuned to a frequency corresponding to resonant electronic transitions in sodium or copper atoms. Molecular ions of double‐stranded oligomeric nucleic acids, with little fragmentation, were observed at masses up to ∼18 500 Da. Single‐stranded nucleic acids could be fragmented by lowering the laser power‐density to reduce the the substrate heating rate. A dimer ion of lysozyme, at mass ∼29 000 Da, was detected at an impact energy on the electron multiplier of only 3.5 keV.
Design and performance of an electrospray ionization source for a doubly‐focusing magnetic sector mass spectrometer
Authors: Gallagher Richard T. , Chapman John R. , Mann Matthias
Published: May 2005

Design considerations for an electrospray ionization source on a double‐focusing magnetic sector mass spectrometer are discussed. A source with two additional pumping stages before the source housing has been constructed. High sensitivity for multiply charged ions from high molecular weight proteins up to 66 kDa is demonstrated with this source.
Fluorine influence in the mass spectrometric patterns in β‐hydroxy alkyl aryl sulphoxides. Part 5
Authors: Seraglia R. , Traldi P. , Bravo P. , Resnati G. , Bortolini O. , Cavicchio G.
Published: May 2005

The electron ionization mass spectrometry of some β‐hydroxy alkyl aryl sulphoxides halogenated in the γ‐position is described and the mechanism of the common fragmentation patterns are discussed with the aid of linked scans at constant B/E, mass‐analysed ion kinetic energy spectra and labelling experiments. The influence of the presence of halogens is also discussed.
Tandem mass spectrometry in the clinical analysis of variant hemoglobins
Authors: Falick A. M. , Shackleton C. H. L. , Green B. N. , Witkowska H. E.
Published: May 2005

A combination of mass spectrometric techniques (electrospray mass spectrometry, liquid secondary‐ion mass spectrometry (LSIMS), tandem mass spectrometry) has been used for variant hemoglobin detection and characterization. Electrospray mass spectrometry allowed analysis of mixtures of intact globins giving the molecuar weights (accuracy 1–2 Da), and information about relative amounts of globins present, simultaneously. Abnormal hemoglobins detected in this way and by other means (screening, clinical symptoms) were fractionated by C‐4 reverse phase high‐performance liquid chromatography (HPLC), and the separated globin chains (or the mixture of whole precipitated globin) were digested with trypsin. The tryptic peptides were separated by C‐18 reverse phase HPLC and analysed by LSIMS to narrow down the mutation site to a single peptide. In some instances, the molecular weight of a variant peptide was sufficient to determine the mutation uniquely. When molecular weight information alone was insufficient to identify the mutation and its site, the peptide was sequenced by tandem mass spectrometry on a 4‐sector instrument. In cases where more than one possible mutation site was present in the peptide and the mutation resulted in a change of only 1 Da in the peptide mass, the resolution and mass measurement accuracy of the 4‐sector machine were esential in determining the correct sequence. The practical application of the methodologies presented is illustrated by the identification and analysis of Hb G‐San Jose, Hb Willamette and Hb D‐Iran.
A membrane‐inlet tandem mass spectrometer for continuous monitoring of volatile organic compounds
Authors: Lauritsen F. R. , Bohatka S. , Degn H.
Published: May 2005

A tandem mass spectrometer designed especially for process control can be simplified in several ways by comparison with those instruments used for analysis. A low‐cost membrane‐inlet triple quadrupole mass spectrometer is described that has been designed especially for process control together with examples of continuous monitoring of different organic compounds in mixtures.
Identification of phosphoramide mustard/DNA adducts using tandem mass spectrometry
Authors: Cushnir Julia R. , Naylor Stephen , Lamb John H. , Farmer Peter B. , Brown Nigel A. , Mirkes Philip E.
Published: May 2005

The reaction pathway of alkylating agents is often exploited in the design of bifunctional anti‐cancer drugs. These drugs form mono‐DNA adducts as well as inter‐ and intra‐strand cross‐linked adducts, notably by reaction at DNA bases, including the N‐7‐position of guanine (G). A positive‐ion fast‐atom bombardment (FAB) mass spectrum of an in vitro preparation of DNA alkylated with phosphoramide mustard (the active metabolite of the anti‐cancer drug cyclophosphamide) indicated the presence of the two mono‐DNA adducts N‐(2‐chloroethyl)‐N‐[2‐(7‐guaninyl)ethyl] amine, designated NORG, and N‐(2‐hydroxyethyl)‐N‐[2‐(7‐guaninyl)ethyl] amine, designated NORGOH, (MH+ 257/259 and 239, respectively) but not the presence of the cross‐linked adduct N,N‐bis‐[2‐(7‐guaninyl)ethyl] amine, designated GNORG (MH+ 372). Using synthetic standards, daughterion spectra of NORG, NORGOH and GNORG were obtained (matrix 0.2 M p‐toluene sulphonic acid in glycerol) by positive‐ion FAB tandem mass spectrometry (FAB‐MS/MS). The daughter‐ion spectra of both mono‐DNA adducts NORG and NORGOH contained a fragment ion at m/z 152 [G + H]+, whereas the cross‐linked adduct, GNORG, showed an ion at m/z221, [MH − G]+. Evidence for the presence of NORG, NORGOH and GNORG in the in vitro preparation was obtained by performing a double parent‐ion scan on m/z 152 and 221. The presence of GNORG was further supported by performing a single parent‐ion scan on m/z 221. The use of this MS/MS technique should eliminate the need for intricate sample purification in the identification of GNORG in biological extracts.
The analysis of smokestack samples for dioxins by gas chromatography/mass spectrometry and gas chromatography/tandem mass spectrometry
Authors: Moore Colin , Moncur John , Jones David , Wright Barry
Published: May 2005

A CONCEPT 1 SQ hybrid mass spectrometer has been used to show the potential of high resolution mass spectrometry and hybrid tandem mass spectrometry (MS/MS) for dioxin analysis. The usual method chosen for gas chromatography/mass spectrometry (GC/MS) determination of polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) is selected‐ion monitoring (SIM) at high resolution, the high resolution imparting a degree of specificity to the analysis. An alternative technique is to use low resolution (1000) gas chromatography/tandem mass spectrometry on a hybrid mass spectrometer, where the specificity of MS/MS is utilized. Data are presented illustrating the potential of both techniques from a single instrument, the CONCEPT 1 SQ.
Deuterium exchange studies in the identification of alkylated DNA bases found in urine, by tandem mass spectrometry
Authors: Cushnir Julia R. , Naylor Stephen , Lamb John H. , Farmer Peter B.
Published: May 2005

Humans are exposed to a large number of carcinogens which may react at various sites throughout the body, including the N‐7‐, N2‐, and O6‐positions of guanine. The effects of this are various but may result in depurination and eventual excretion of the modified base in the urine. Various alkylguanine derivatives with substituents at the N‐7‐, N2‐ and O6‐positions were synthesized and daughter‐ion spectra obtained. Apart from the methyl and dialkylguanines all other spectra exhibited an ion at m/z 151 using electron ionization (EI) and m/z 152 using fast‐atom bombardment (FAB). The daughter‐ion spectra of dialkylguanines contained an ion at m/z 150 (EI). Hence, scans of m/z 150 and 151 using EI, to detect all parent‐ions from which they are formed (parent‐ion scans) should indicate the presence of alkyl and dialkylguanine bases in a complex biological matrix such as human urine. Parent‐ion scans of m/z 150 and 151 (EI) of a partially purified human urine sample exhibited numerous ions, including a prominent ion at m/z 179. A daughter‐ion spectrum of m/z 179 revealed fragment ions that suggested the presence of N2‐dimethylguanine and an ethylated guanine. Any confusion due to the presence of daughter ions from different alkylguanines in the same spectrum can be resolved by the fact that an ethylated guanine has four exchangeable protons, whereas N2‐dimethylguanine has only three. By performing hydrogen/deuterium exchange it is possible to distinguish the N2‐dimethylguanine from ethylated guanine isomers. Daughter‐ion spectra of m/z 180–183 (EI) and 182, 184 (FAB) on human urine enabled us to identify the presence of N2‐dimethylguanine and N2‐ethylguanine.
Theoretical studies of ion trajectories in quadrupole systems
Authors: Barber M. , Gordon D. B. , Woods M. D.
Published: May 2005

A brief introduction to the mathematical theory of quadrupole systems is given and the configuration of hyperbolic and circular cross‐section rods is considered. Application of the theory of electrostatics to the latter case indicates that multipole contributions to the field occur which influence the ion trajectories. We have considered motion in the x‐z plane of a static quadrupole (DC‐only) for the simplest case of a 1:1 combination of quadrupole and dodecapole contributions. The quadrupole contribution to ion motion is simple harmonic and may be described as a sine function, whereas the dodecapole contribution may only be obtained by solving the appropriate elliptic integral. This solution gives rise to a sine (amplitude) or sn function. In the case of collision cells (RF‐only) we have attempted to solve the Mathieu equation both analytically and numerically. Both stable and unstable trajectories may be calculated from these solutions and are presented in various formats. Some consideration is also given to the problems of collisional interaction and the associated difficulties likely to be encountered when the study is expanded to include this phenomenon.
The use of tandem mass spectrometry for the differentiation of bile acid isomers and for the identification of bile acids in biological extracts
Authors: Eckers Christine , New Anthony P. , East Philip B. , Haskins Neville J.
Published: May 2005

Tandem mass spectrometric (MS/MS) techniques have been widely used for the differentiation of isomeric compounds, since their spectra may show differences sufficient to distinguish between them. There are several different ways by which the MS/MS data can be obtained depending on the energies of the ions and the collisions. In this paper MS/MS spectra have been obtained for a group of isomeric bile acids using: 1, low‐energy ions and low‐energy collisions in a triple quadrupole mass spectrometer by liquid chromatography/MS/MS; 2, high‐energy ions and low‐energy collisions in a hybrid mass spectrometer by fast‐atom bombardment MS/MS. Liquid chromatography combined with tandem mass spectrometry (LC/MS/MS) has also been used to identify the bile acids present in biological matrices such as bile extracts.
Fragmentation of the metastable dieckmann ester molecular ion: Loss of carbon monoxide
Authors: Morizur Jean‐Pierre , Martigny Isabelle , Taphanel Marie‐Hélène , Tortajada Jeanine
Published: May 2005

The structure of the ionized enol of methyl 4‐buteneoate ([10]+˙) is proposed for the [M‐CO]+˙ ions from the metastable Dieckmaann ester 2‐oxocyclopentanecarboxylate molecular ion. This proposal is based on a comparison of the metastable‐ion mass spectra and the kinetic energy releases of these ions with the same data of an authentic ion [10]+˙.
Analysis of arachidonic‐acid‐containing molecular species in glycerophospholipid classes from rat kidney by fast‐atom bombardment mass spectrometry
Authors: Chen Su , Mariot Roberta , Kirschner Günther , Favretto Donata , Traldi Pietro
Published: May 2005

The qualitative analysis of the molecular species of phosphatidylinositol, phosphatidylethanolamine, phosphatidylcholine and phosphatidylserine from a rat kidney, by fast‐atom bombardment mass spectrometry after separation and purification by liquid chromatography is described. The present results indicate that a high content of arachidonic‐acid‐containing molecular species within major glycerophospholipid classes is present in this biological sample.
Mass spectral study of 2‐adamantanone
Authors: Srzić Dunja , Vinković Vladimir , Mlinarić‐Majerski Kata
Published: May 2005

The mass spectral fragmentation of 2‐adamantanone has been investigated using its specifically labelled monodeuterated derivatives (in positions 1‐, 4‐exo‐, 4‐endo‐, 5‐ and 6‐) and dideuterated derivatives (in positions 4,4‐ and 6,6‐). The mass spectrum of 2‐adamantanone is generally poor in fragments showing the molecular ion as the base peak, the characteristic m/z 117, 104, 93, 91, 80, 79, 72, 67 and 53 fragments, as well as an unusual loss of water. The mass spectra of deuterated compounds favours the assumption of hydrogen randomization prior to the fragmentation of the molecular ion. In contrast, the formation of [C4H8O]+·, m/z 72 does not involve any major hydrogen scrambling.
Oil/oil correlation based on gas chromatographic/mass spectrometric analysis of polycyclic biomarkers
Authors: Šban M. M. , Jovančićević B. S. , Glumičić T. , Dogović N.
Published: May 2005

Polycyclic biomarkers such as steranes, diasteranes and tri‐, tetra‐ and pentacyclic terpanes in the hydrocarbon fraction of oils were studied by gas chromatographic/mass spectrometric (GC/MS) analysis in order to correlate six crude oils. Distribution and abundance of these biomarkers were determined for the samples from the Kikinda, Mokrin (Vojvodina) and Požarevac oil fields (two samples for each oil field). The SIM (single‐ion monitoring) method was used for the analysis of steranes and terpanes. Individual steranes, terpanes and their stereoisomers were identified by the comparison of obtained retention times with those quoted in the literature. On the basis of the results obtained, it can be concluded that the oils from the Kikinda and Mokrin (Vojvodina) fields belong to the same genetic type, while the oil from the Požarevac field belongs to another type. It was also found that the oils from the Kikinda and Mokrin fields were of a higher degree of maturity than the oils from the Požarevac field.
Mass‐analysed temperature‐programmed desorption from glassy carbon
Authors: Laušević M. , Popović A. , Laušević Z.
Published: May 2005

The modification of the glassy carbon surface in contact with AgNO3 solution has been studied using X‐ray diffraction and Brunauer, Emmett and Teller (BET) surface analysis methods. The deposition of metallic silver, confirmed by X‐ray analysis, affected the pore system resulting in a decrease of surface area and pore volume. The thermal decomposition of the surface oxide species resulting in desorption of H2O, CO and CO2 as major gas products has been studied using a temperature‐programmed desorption method combined with a mass spectrometric analysis of the desorbed gases. The desorption energies have been calculated using a peak position method. It has been concluded that the silver deposition on the glassy carbon surface contributes to the increased stability of surface oxide species.
UV‐laser‐induced desorption mass spectrometry of insulin, substance P and A4 amyloid protein fragments from synthetic fibrillary aggregates
Authors: Perera I. K. , Candy J. M. , Håkansson P. , Oakley A. E. , Brinkmalm G. , Sundqvist B. U. R.
Published: May 2005

Matrix‐assisted UV‐laser‐induced desorption has previously enabled the molecular weights of non‐aggregated peptides, polypeptides and proteins to be determined using mass spectrometry. We now report that this technique can be used to disaggregate and determine the molecular weights of peptides, polypeptides and proteins, present as β‐pleated sheet fibrillary polymers. It was found that the molecular weights of the individual fibril constituents could be determined at subpicomolar concentrations and at a high accuracy. The unrivalled sensitivity and ability to disaggregate fibrillary proteins show the potential of this technique for characterizing the proteins associated with pathological features which occur in a number of diverse disease states.
Electrospray mass spectrometry of recombinant growth hormones
Authors: Baczynskyj Lubomir , Bronson George E.
Published: May 2005

The electrospray mass spectra of several standard proteins were recorded and their molecular weights determined. These were compared to Literature values obtained by other laboratories. The agreement was quite good. Seven recombinant growth hormones were then investigated by this technique. The determined molecular weights were in agreement with the theoretical values. Differentiation between six of the seven analogs could be made on the basis of the molecular weight determinations. Two of these analogs differed in molecular weight by only 1 Da and the accuracy of the mass measurements was not sufficient for distinguishing these two homologous proteins. The influence of solvent on the mass accuracy determinations was studied. It appears that solvents form clusters with the proteins in the electrospray ionization method. These clusters broaden the peaks corresponding to the multiply charged ions of the proteins and make the detemination of centroids more difficult.
Microstructure of co‐polymers by fast‐atom bombardment mass spectrometry
Authors: Montaudo Giorgio , Daolio S.
Published: May 2005

The assumption on which both the structural analysis of polymers and the sequential of co‐polymers by fast‐atom bombardment mass spectrometry (FAB‐MS) is based, is that the ion detected in the FAB spectra do originate from species already present in the polymeric samples, and that the bombardment by fast atoms does not produce the fragmentation of macromelecules. FAB spectra do not yield direct structural information on large macromolecules, but such information can be deduced from the structural analysis of relatively low molecular weight species. Therefore, in a series of recent studies, FAB‐MS has been used to identify the oligomers formed in the partial degradation of several co‐polymers, and the results obtained have yieled detailed information on the microstructure of the materials investigated.
Negative‐ion fast‐atom bombardment mass spectra of pyrazolylborates with various matrices
Authors: Aubagnac Jean‐Louis , Claramunt Rosa‐Maria , Lopez Conception , Elguero José
Published: May 2005

Negative‐ion fast‐atom bombardment mass spectra of pyrazolylborates with various matrices (glycerol, m‐nitro‐benzyl alcohol, magic bullet, tetraethyleneglycoldiethylether) have been studied and compared. Collisionally‐activated dissociation spectra gave information on ion structure.
Properties of matrix‐assisted laser desorption. Measurements with a time‐to‐digital converter
Authors: Ens W. , Mao Y. , Mayer F. , Standing K. G.
Published: May 2005

Some properties of matrix‐assisted laser desorptio have been studied using single‐ion‐counting methods and a time‐to‐digital converter. The methods allow examination of the process for irradiances near the reported threshold for observation with a transient recorder. All measurements were made using bovine insulin as a test compound. We presernt direct evidence that an irradiance threshold near 106 W cm−2 exists for ion production, and that the process in a collective effect, either involving a large number of molecular ions (∼104)in a successful event or none at all. Above the threshold, the yield is found to scale with a high power (4th to 6th) of the irradiance. Measurements of initial velocity distributions indicate an axial velocity spread corresponding to ∼50 eV and a radial velocity spread corresponding to ∼2.4 eV. Thus the ejection or extraction mechanism appears to be strongly asymmetric.
Matrix‐assisted laser desorption of large biomolecules with a TEA‐CO2‐laser
Authors: Overberg A. , Karas M. , Hillenkamp F. , Cotter R. J.
Published: May 2005

Matrix‐assisted desorption/ionization of large biomolecules with a TEA‐CO2laser with a warelength of 10.6 μm is demonstrated. TEA‐CO2LDI mass spectra are almost identical to those obtained with the Er‐YAG (2.94 μm) infra‐red (IR) laser and very similar to UV‐LDI spectra. Most of the matrices usable for Er‐YAG IR‐LDI have been tested at 10.6 μm with success, and the main features of IR‐LDI e.g., the tendency towards the formation of higher chargers is shown.
Pulse timing and optical interface between a neodymium: Yttrium aluminum garnet laser and a Fourier transform ion cyclotron resonance mass spectrometer
Authors: Liang Zhenmin , Ricca Tom L. , Marshall Alan G. , Ghaderi Sahba
Published: May 2005

Laser desprption/ionization combined with pulsed (time‐of‐flight or Fourier transform ion cyclotron resonance) mass spectrometric detection is a powerful technique for analysis of involatile compounds and mixtures. Such experiments were originally conducted with pulsed CO2lasers. Although a pulsed CO2laser can be operated in single‐shot mode, Nd: YAG lasers perform best with multiple flashes for warm‐up before the final Q‐switch output light pulse, thus creating the need to synchronize the desired final laser‐output pulse with the event sequence for mass spectrometric analysis. In this paper, we describe a new and simple interface (both optical and electronic components) between a Continuum (formerly Quantel) Model YG 660A Nd: YAG laser and an Extrel FTMS‐2000 mass spectrometer. The optics are modified from a prior pulsed CO2laser interface from Extrel. Synchronization betweem th Nd: YAG laser and the mass spectrometer event sequence is achieved by means of a simple timing circuit that uses an inexpensive pulsing device and is triggered by pulses generated directly from the Extrel 1280 data system and cell controller, in contrast to the only prior published method that required an auxiliary microcomputer. The present interface method is highly flexible, and makes possible complex sequence events involving laser pulses for e.g.: desorption/ionization of solids; photoionization of gaseous neutrals; and photodissociation and photodetachment of gaseous ions.
Retrosynthesis vs ketene loss in electron‐ionization‐induced decompositions of 1,5‐benzodiocapine, 1,5‐benzodiazepine, 1,5‐benzodithiepine, 1,5‐benzoxazepine and 1,5‐benzoxathiepine
Authors: Bopnsignore Leonardo , Loy Giuseppe , Maccioni Elias , Podda Gianni , Seraglia Roberta , Traldi Pietro , Schlunegger Urs
Published: May 2005

The 70 eV electron ionization mass spectrometry of the title compounds has shown the presence of two concurrent primary decomposition pathway, corresponding to the retrosynthetic process and to CH2CO loss. The yields of the two pathways can be related tothe XCO bond strengths: as the XCO bond becomes weaker, [MCH2CO]+˙ ion formation is favoured.
The analysis of thiocarbamides by gas chromatography/negative‐ion chemical‐ionization mass spectrometry
Authors: Watson D. G. , Bates C. D. , Skellern G. G. , Mairs R. , Martin S. , Brooks C. J. W.
Published: May 2005

Thiocarbamides were converted to their di‐N‐pentafluorobenzyl (PFB) derivaties and analysed by gas chromatography/negative‐ion chemical‐ionization mass spectrometry with methane as reagent gas. The PFB derivatives of the 2‐thiouracils gave mass spectra in which the ion current was carried largely by an ion arising from [MPFB]−. The derivative was used in the determination of the uptake and metabolism of thiocarbamides by cultures of melanoma cells.
Determination of the amino acid sequence of cystine‐containing peptides by tandem mass spectrometry
Authors: Despeyroux Dominique , Bordas‐Nagy Jozsef , Jennings Keith R.
Published: May 2005

A method has been developed for the determination of the amino‐acid sequence of a cyclic peptide containing cystine. It is based on the reduction of the peptide in a reductive matrix prior to ionization by fast‐atom bombardment. The amino‐acid sequence of the resulting linear peptide is then determined by tandem mass spectrometry from the spectrum produced by the collision‐induced decomposition of the [M+H]+ ion of the peptide.
Concerning the formation of C3H3O+ and C4H7+ ions from the cyclohexanone molecular ion
Authors: Lebedev Albert T. , Hayes Roger N. , Bowie John H.
Published: May 2005

The base peak (m/z55, C3H3O+) in the mass spectrum of cyclohexanone is shown to be formed by a number of processes, viz from the molecular radical cation, from [MC2H4]+˙ species, and from an [MC3H6]+˙ ion. The ion C4H (the minor contributor to m/z55) is formed by at least five routes from the molecular ion.
Mass spectral fragmentation patterns of deuterated hexanitrobibenzyl and hexanitrostilbene
Authors: Yinon Jehuda , Fraisse Daniel , Dagley Ian J. , Lifshitz Chava
Published: May 2005

Mass‐analysed ion kinetic energy (MIKE) spectrometry with collision‐induced dissociation (CID) has been used to study the fragmentation processes of the MH+ ions produced by chemical ionization (CI) of a series of deuterated hexanitrostilbene (HNS) and hexanitrobibenzyl (HNBB) compounds. Typical fragment ions obtained in both groups were due to loss of OR′, 2OR′ and NO2 and due to the cleavage of the CC single bond in HNBB and of the double bond in HNS. In HNS there is a preferential loss of NO. A great similarity was observed between the fragmentation pattern of 2,4,6‐trinitrotoluene (TNT) and that of HNS. In negative‐ion chemical ionization (NCI) the fragment ion which forms the base peak in the mass spectra of the HNS compounds is the [(M/2)+O]− ion, while in the HNBB compounds it is the [M/2]− ion.
Desorption of ions from locust tissues. I. Behaviour of E‐destruxin using positive‐ion fast‐atom bombardment mass spectrometry
Authors: Lange C. , Mulheim C. , Cherton J.‐C. , Cassier P. , Vey A. , Pais M.
Published: May 2005

Detoxification of E destruxin in E‐diol‐destruxin in vivo in Locusta migratoria locust is demonstrated using direct fast‐atom bombardment (FAB) mass spectrometry without the need for extraction or purification. Organs and biological fluids are used as biomatrices for the FAB desorption process.
High temperature mass spectrometry in materials research
Authors: Hilpert K.
Published: May 2005

Vaporization is an important property in materials research since it limits the use of the materials at high temperatures and since valuable thermodynamic data can be determined from vapour pressures. High‐temperature mass spectrometry is the most versatile method for the elucidation of vaporization processes. Numerous results have been obtained. This article describes the fundamentals of the method and gives examples of its application. These examples describe the determination of thermodynamic properties for the gaseous species and condensed phases. The materials considered are salts, alloys and graphitic materials. They are of interest for metal halide lamps, superalloys, and nuclear reactors.
Analysis of bovine β‐casein tryptic digest by continuous‐flow fast‐atom bombardment mass spectrometry
Authors: Jones D. S. , Heerma W. , van Wassenaar P. D. , Haverkamp J.
Published: May 2005

Liquid chromatography/fast‐atom bombardment mass spectrometry was used to partially confirm the amino‐acid sequence of the protein, β‐casein. The study demonstrates that the technique is capable of the rapid and accurate identification of peptide fragments from tryptic digests and that chromatograrphic integrity is maintained during the analysis. The power of the technique derives from the ability to determine both the retention time and the molecular weight of the eluting components. Each of the components yields a prominent pseudo‐molecular ion (MH+), the majority exhibiting sufficient fragmentation to confirm their structure unambiguously.
Differentiation of taurochenodeoxycholate from taurodeoxycholate by collision‐induced dissociation of pseudomolecular anions generated by fast‐atom bombardment
Authors: Griffiths William James , Egestad Börje , Sjövall Jan
Published: May 2005

The conjugated bile acids taurochenodeoxycholate and taurodeoxycholate are indistinguishable from analysis of their fast‐atom bombardment spectra. Both the positive‐ and negative‐ion spectra show prominent pseudomolecular ions, but little fragmentation. Collision‐induced dissociation of the negative pseudomolecular ions reveal structural differences between the two isomers which are evident in the resultant daughter‐ion spectra. Thus the two isomers can be differentiated.
An expert system for inferring structures of organic compounds from their mass spectra
Authors: Sridhar M. P. , Menon A. G. , Sastry P. S. , Mathur D.
Published: May 2005

Development of an ‘expert system’ for elucidation of structures of acyclic organic compounds is described. An expert system is a computer program that embodies some of the heuristic problem‐solving knowledge of human experts so that it can effectively be used as an aid to decision making. The expert system described in this paper is intended to assist a chemist in arriving at plausible structures, the input data being the mass spectrum, molecular formula and presence (if known) of functional groups. The program generates chemically possible structures for the given molecular formula and can use, where available, the constraints imposed by the mass spectrum of the compound and by any known functional groups. The program makes use of a new algorithm for obtaining a canonical representation of structures and a new heuristic for incorporating constrains of the mass spectrum. This work constitutes a case study of the application of artificial intelligence techniques in chemistry and the material presented highlights this motivation.
Charge‐separation reactions of N2O cations formed by low‐ and high‐energy ionization
Authors: Eland J. H. D. , Murphy V. J.
Published: May 2005

Triple and quardruple coincidence charge‐separation spectra of nitrous oxide ionized by single low‐energy photons and by high‐energy electrons are reported. Low‐lying states of the molecular dication, which are populated at all energies, dissociate mainly into ion pairs by two‐body reactions. The reaction producing N++N+O+ is weak at low excitation energy and may occur by a very fast secondary dissociation of intermediate dinitrogen ions. At high energy a major new effect is triple ionization followed by dissociation into three atomic ions. These ion triple produce a significant spurious contribution to the spectrum of ion pairs, and several sorts of pair whih appear at high energy are mainly or entirely artifacts of this type.
Anionic rearrangement in the gas phase. The collision‐induced dissociations of deprotonated 2‐diazo‐2‐cyanoacetamides
Authors: Lebedev Albert T. , Bakulev Vasily A. , Hayes Roger N. , Bowie John H.
Published: May 2005

Peak‐width measurements and product‐ion studies show that deprotonated 2‐diazo‐2‐cyanoacetamides and the isomeric 4‐cyano‐5‐hydroxy‐1,2,3‐triazoles fragment through a common intermediate to form (OC3N)− as base peak.
Charge stripping C
Authors: Lifshitz C. , Iraqi M. , Peres T. , Fischer J. E.
Published: May 2005

Measurements of the translational energy loss accompanying the charge‐stripping reactions M++N→M2++N+e− and M2++N→M3++N+e− have been performed for C, C and C, C respectively. The energy nesessary to remove the second electron from Buckminsterfullerene was determined, Q=IE(C→C=12.25±0.5 eV.
Collisional spectroscopy approaches in the characterization of 7‐α‐ and 7‐β‐hydroxycholesterol
Authors: Favretto Donata , Guidugli Federico , Seraglia Roberta , Traldi Pietro , Ursini Fulvio , Sevanian Alex
Published: May 2005

High‐ and low‐energy collision experiments, by means of double‐focusing and ion‐trap mass spectrometers, respecstively, performed on the M+˙ and [MH2O]+˙ ions of 7‐α‐ and 7‐β‐hydroxycholesterol lead to a clear structural characterization of the two stereoisomers. In particular, the β isomer shows peculiar fragmentation pathways due to interaction between the hydroxyl group in position 7‐β and the hydrogen atom on C(15).
Direct evidence for degradation of esperamicin A1 with thiol confirmed by fast‐atom bombardment mass spectrometry
Authors: Takayama Mitsuo , Nomura Taro , Konishi Masataka
Published: May 2005

A degradation of esperamicin A1, which is a potent antitumor antibiotic having DNA‐cleaving activity, was studied by fast‐atom bombardment (FAB) mass spectrometry. It was proved that the degradation easily occurs via the thiol group(s) in the matrix solution and not by a FAB‐induced reaction. It was concluded that from the FAB mass spectra of all non‐volatile compounds, the molecular weight should be determined by using at least two chemically different matrices.
Collision‐induced liquid secondary‐ion mass spectra of oxytocin derivatives. A study of the influence of modifications in the disulfide bond on the adjacent peptide bond cleavage
Authors: Malát Jan , Ubik Karel , Lebl Michal
Published: May 2005

The influence of the inductive effect of modifications in the disulfide bridge in oxytocin analogs on the cleavage of the neighboring peptidic bond was studied. A correlation between the inductive constant of the group in the disulfide bridge and the particular fragment ion abundance was observed.
Fast protein sequence determination with matrix‐assisted laser desorption and ionization mass spectrometry
Authors: Schär Martin , Börnsen K. Olaf , Gassmann Ernst
Published: May 2005

Measurement and identification of digested peptides by matrix‐assisted laser desorption and ionization mass spectrometry (LDI‐MS) is demonstrated. Synthetic human parathyroid hormone, pTH (1–34), with molecular mass of 4117.8 Da was digested with carboxypeptidases Y and B and the seqence of 14 amino acids from the C‐terminus of the peptide was determined by analyzing the molecular mass of the truncated peptides. Furthermore, a tryptic digestion of PTH (1–34) was carried out and a molecular mass map of pTH (1–34) was obtained. With the results of the proteolytic digestion a rapid confirmation of the amino‐acid sequence of the protein was possible. It is shown that the results of the trypitc digestion can be used for the unambiguous identification of the amino acid residues Lys and Arg, which cannot be distinguished with a mass spectrometer because of their equal norminal masses. Several advantages of amino acid sequence determination by the combination of digestion and LDI‐MS are obvious: high sensitivity in the low pmol range, fast digestin time due to high enzyme/substrate rations, quantification is unnecessary because the amino acids are identified by their molecular mass differences, the low chemical expenditure for the digestions and the accuracy of the sequence determination. Measurements with LDI‐MS are fast: sample preparation and the measurement take only a few min. The mass determination and amino acid sequence is completely unimpaired by amino acid contaminations or impurities in the sample. The sensitivity of the method is in the low pmol to fmol range and thus comparable to other analytical methods.
Fast‐atom bombardment mass spectrometry of peptide derivatives with diethylpyrocarbonate
Authors: Foti Salvatore , Marletta Donata , Saletti Rosaria , Petrone Goffredo , Daolio S.
Published: May 2005

The reaction products of five peptides with diethylpyrocarbonate, a site‐specific reagent for histidine residues and amino groups, have been synthesized, isolated by high‐performance liquid chromatography (HPLC) and identified by fast‐atom bombardment (FAB) mass spectrometry. Peptides containing histidine, as well as compounds resulting from the N‐carboethoxylation of terminal amino groups and the histidine imidazole ring, provide a derivative produced by cleavage of the histidine heterocyclic ring through a Bamberger reaction. The main masss spectral features of these derivatives are discussed in comparison with structurally related compounds. HPLC along with with FAB MASS spectrometry shows itself to be a suitable technique for the characterization of these structures.
A phenomenological description of a black hole for collisionally induced decomposition products in ion‐trap mass spectrometry
Authors: Guidugli Federico , Traldi Pietro
Published: May 2005

Through extensive studies of collisionally induced decompositions of different precursors by ion‐trap mass spectrometry, the presence of a shadow region was demonstrated. If fragment ions fall into the stability diagram at a qz value of ∼0.78, their absolute intensities drop almost to zero. In order to test this phenomenon, different precursors and different collisionally produced fragment ions have been examined and in every case the fragment at qz = 0.78 disappeared, suggesting that such qz values can be considered as black holes in the microcosmos of the ion‐trap mass spectrometer.