bluuebunny/crossref_metadata_2025 huggingface dataset:
A high resolution gas chromatographic/mass spectrometric method for the determination of N‐0923 in human and monkey plasma
Authors: Zavitsanos Paul A. , Siddiqui Waheed , Curtis Michael
Published: May 2005

A method that combines gas chromatography and mass spectrometry (GC/MS) for the determination of N‐0923 in human and monkey plasma is detailed. This novel drug holds promise for the treatment of Parkinson's disease. Clinical use of N‐0923 will result both in low peak plasma concentrations and in a short half‐life; consequently, a highly sensitive method will be required. Previous methods using high‐performance liquid chromatography with electrochemical detection have given reliable data in high dose studies in animals to 0.3–1.0 ng/mL in plasma but are not considered adequate for studies at clinical levels in humans. The data in this paper will show that GC/MS can offer a new direction in the determination of N‐0923 in human and monkey samples, with reliable data to 25 pg/mL in plasma. This method is presented as a novel approach to the determination of N‐0923, and as a starting point for further development.
Internal ion impact ionization for Fourier‐transform ion cyclotron resonance
Authors: Wood Troy D. , Marshall Alan G. , Schweikhard Lutz
Published: May 2005

A general scheme for ionization and fragmentation of ions in Fourier‐transform ion cyclotron resonance mass spectrometry (FT‐ICRMS) is introduced. The technique is based upon excitation of high‐frequency (i.e. lowmass) primary ions (e.g. N, Al+, H2O+·) which may be generated by standard ionization methods (e.g. electron ionization or laser desorption) inside the trap. Generation of the primary ions is followed by excitation of their cyclotron motion to high translational energy to serve as projectile ions. The projectiles serve two functions: to ionize neutral gas atoms and/or molecules (secondary ions) within the trap internal ion impact ionization (IIII), and to collisionally activate the secondary ions to induce fragmentation. Ionization by IIII is analogous to charge‐exchange ionization, in which a primary ion reacts with neutral analyte to produce ionization. When the projectile ions' cyclotron orbits are not excited (even for very long delay periods between ionization and detection), lower ion abundances are observed for the secondary ions derived from the neutral analyte(s), verifying that high energy ion impact must be responsible for the relatively high ion abundances observed when projectile cyclotron motion is excited: i.e., the mechanism of IIII is likely to be high‐energy charge exchange. Several advantages of the new technique include: accessibility of very high impact energy (keV) in FT‐ICRMS in both the laboratory and the center‐of‐mass frames of reference; ease in controlling the average energy transferred from projectiles to sample neutrals by moderation of the projectile ion's cyclotron radius; and the high ion‐molecule reaction rates attainable in FT‐ICR due to the long path length for trapped primary projectile ions at low pressure. Theory of ion formation and the problems associated with this technique (e.g. formation of secondary ions at different pre‐excitation ICR orbits) are discussed.
In situ analysis of a new perylene quinone in lichens by Fourier‐transform laser microprobe mass spectrometry with external source
Authors: Mathey Annick , Van Roy Wim , Van Vaeck Luc , Eckhardt Gert , Steglich Wolfgang
Published: May 2005

The application of Fourier‐transform laser microprobe mass spectrometry to lichens is described. The in situ detection of a new perylene quinone in samples of the tropical species Laurera sanguinaria Malme and Graphis haematites Fée was achieved with minimal specimen preparation. The high mass resolution and mass accuracy of the instrument eliminates the need for additional characterization of the isolated substances by high resolution electron impact mass spectrometry and direct introduction probe.
Mass spectrometric investigation on some pyrilium salts by different. Ionization methods and metastable ion studies
Authors: Hadjieva P. , Deligeorgiev T. , Fontana S. , Catinella S. , Traldi P.
Published: May 2005

A series of pyrilium hydrochlorides (Py+ClO−4) have been studied by means of both electron ionization and fast‐atom bombardment (FAB) methods. Only for some compounds does electron ionization show the formation of Py+, together with [Py—H]+· ions. Metastable ion data indicate that the former also originate through H· loss when their formation could be explained by loss of perchloric acid through a thermal process directly from the salt. Many fragment ions, related to the original structures, are also detected. In contrast, in FAB conditions, all the compounds show the formation of Py+ without any fragmentation products, proving its effectiveness in the easy identification of the related molecular species. Only by the mass‐analyzed ion kinetic energy spectra of Py+ ions can a valid characterization of the compounds under study be achieved.
A review of the collision‐induced dissociations of deprotonated dipeptides and tripeptides. An aid to structure determination
Authors: Waugh Russell J. , Bowie John H.
Published: May 2005

The structures of underivatized di‐ and tripeptides may be determined from a consideration of the collision‐induced dissociations of their [M—H]− ions. There are three types of fragmentation, viz. (i) the backbone cleavage which provides sequencing information, (ii) α side‐chain cleavage irrespective of the position of the amino acid residue, and (iii) cleavages which are characteristic of amino acid residues in specific positions, in particular the N‐ or C‐terminal positions.
Selective injection of laser desorbed ions into a quadrupole ion trap with a filtered noise field
Authors: Garrett A. W. , Cisper M. E. , Nogar N. S. , Hemberger P. H. , Goeringer Douglas E.
Published: May 2005

We demonstrate the advantages of utilizing a broad‐band filtered noise field (FNF) for preferential mass injection of laser desorbed ions into an ion‐trap mass spectrometer (ITMS). The FNF waveform is applied to the endcap electrodes of the ITMS during the laser‐desorption period, and its amplitude and frequency spectrum are adjusted to resonantly eject all ions except those with selected mass‐to‐charge ratios. In single‐pulse laser desorption, the FNF rapidly ejects desorbed matrix ions without reducing the number of target ions that are trapped. When the FNF is used in conjunction with multipole laser‐desorption events, accumulation of target m/z ions results in a 40‐fold increase in sensitivity over single‐shot laser desorption. In addition, the application of sequential filtered noise fields for multiple stages of mass spectral interrogation is demonstrated.
The application of capillary electrophoresis/mass spectrometry using negative‐ion electrospray ionization to areas of importance in the textile industry
Authors: Tetler Lee W. , Cooper Paul A. , Carr Chris M.
Published: May 2005

The feasibility of using capillary electrophoresis/mass Spectrometry, with negative‐ion electrospray ionization, for applications of relevance to the dyeing and textile industries has been shown. Structurally similar examples of solubilized vat dyes of different halogen content have been separated and identified with a view to investigating the photodegradation processes which occur when the dyes are subjected to UV light. Separations of the various species formed when a mordant dye is chrome treated are also presented, indicating the ability to study complex formation arising from the different chrome dyeing methods.
Optimization of skimmer voltages of an electrospray ion source coupled with a magnetic sector instrument
Authors: Murata Hiroshi , Takao Toshifumi , Shimonishi Yasutsugu , Matsuo Takekiyo
Published: May 2005

An electrospray ion source designed for a magnetic sector instrument usually has two skimmers, which are located behind a capillary exit with separate pumping stages to reduce the pressure from that of ambient air to a valve suitable for the sector instrument. This work describes an evaluation of these two skimmer voltages with respect to the charge‐state distributions and the focusing efficiency of ions. The skimmer voltages were found to be closely related to the m/z values of the detected ions. The optimal difference voltage between skimmers 1 and 2 increased in proportion to the m/z values of the ions, irrespective of the molecular masses of the associated substances. This phenomenon is ascribable to the ion‐focusing effect in this region rather than to the effects of energetic collisions in the region of the skimmers, and suggests that the skimmer voltages should be adjusted in accordance with the m/z values of the detected ions for efficient acquisition of all distributed ions. The work demonstrates the functional role of the skimmers in electrospray ionization mass spectrometry with a magnetic sector instrument by examining several types of peptides and proteins, as well as an analysis of a complex mixture of peptides.
Influence of laser focusing in matrix‐assisted laser desorption/ionization
Authors: Riahi Karim , Bolbach Gérard , Brunot Alain , Breton Francis , Spiro Marenglen , Blais Jean‐Claude
Published: May 2005

The influence of laser focusing on the target in matrix‐assisted laser desorption/ionization (MALDI) has been studied. The emission of stable and metastable molecular ions of bovine insulin depends on both the laser energy and the distance between the target and the laser focal plane. The results clearly show that the laser fluence is the important parameter in MALDI. The fluence threshold of metastable‐ion emission is higher than that of stable‐ion emission. Beyond this threshold, the emission of stable ions reaches a plateau. This is due to the spatial inhomogeneity of the laser energy distribution. A phenomenological model including two fluence thresholds for the stable‐ and metastable‐ion emission has been developed and compared to the experimental data.
The use of low‐energy collisionally activated dissociation negative‐ion tandem mass spectrometry for the characterization of dog and human urinary metabolites of the drug BW 1370U87
Authors: Taylor Lester C. E. , Johnson Robert L. , John‐Williams Lisa St. , Johnson Tom , Chang Sai Y. , Baillie T. A.
Published: May 2005

Liquid chromatography (LC) combined with atmospheric pressure chemical ionization mass spectrometry was used to identify phase I and II metabolites of the drug BW 1370U87 in dog and human urine. Additional analysis of individual high‐performance liquid chromatograph fractions collected from dog urine by combined gas chromatography/mass spectrometry identified one metabolite which was not detected by LC/MS methods. Using negative‐ion LC/MS, the majority of BW 1370U87 metabolites in human urine were identified as glucuronic acid conjugates of phase I oxidative metabolites. The negative‐ion fragmentation produced by low‐energy collisionally activated decomposition (CAD), studied by tandem mass spectrometry experiments, confirmed that these compounds were drug‐related and allowed metabolite structures to be assigned. Product‐ion spectra of the metabolites were dominated by the loss of neutral molecules from even‐electron deprotonated [M − H]− ions.
Collision‐induced dissociation of some protonated peptides with and without mass selection
Authors: Hamdan Mahmoud , Curcuruto Ornella
Published: May 2005

Collision‐induced dissociation (CID) of several protonated peptides formed by positive‐ion electrospray (ES+) and by Cs+ fast‐ion bombardment are reported. The CID spectra of ions formed by the first ionization method were effected at elevated extraction cone voltages within the ion source of a single quadrupole instrument, while linked‐fields‐scan measurements at constant B/E of ions formed by the latter technique were performed within the collision cell of a trisector instrument. For molecular masses below 1000 Da, the two sets of spectra yielded identical sequencing information; however, for higher molecular masses the similarity was less evident. This divergence between the two sets of measurements is partially attributed to dominant doubly charged ions and less efficient dissociation of sodium adduct ions at elevated cone voltages.
A comparison of the mass spectrometric behaviour of trimethylindium adducts with N,N,N′‐triathylethylenediamines and of the related dimethylindium N,N,N′‐trialkylethylenediamido derivatives
Authors: Carta Giovanni , Rossetto Gilberto , Marco Nadia Di , Zanella Pierino , Favretto Donata , Traldi Pietro
Published: May 2005

The electron ionization mass spectrometric behaviour of dimethylindium N,N,N′‐trialkylethylenediamides and, for comparison, of trimethylindium adducts with the related N,N,N′‐trialkylethylenediamines, is discussed. The extensive decomposition processes observed under fast‐atom bombardment conditions are rationalized in terms of the condensed‐phase reactivity of the compounds under study.
An inductive detector for time‐of‐flight mass spectrometry
Authors: Park Melvin A. , Callahan John H. , Vertes Akos
Published: May 2005

In this paper we describe the underlying principles of, and demonstrate some of the attributes of, an inductive detector for use in time‐of‐flight mass spectrometry. Unlike a microchannel plate detector, the detection efficiency of the inductive detector is not dependent on ion velocity. Also, the inductive detector cannot be saturated in the same manner as a microchannel plate detector. Because the inductive detector detects only charged species, the neutral species normally observed in linear time‐of‐flight matrix‐assisted laser desorption/ionization spectra do not appear in spectra obtained with the inductive detector. Further, price and availability of the material needed to fabricate an inductive detector are virtually independent of detector size. Perhaps one of the most important features of the inductive detector is that it is a largely non‐destructive detector.
Mass spectra of some 2,4‐disubstituted 1,3‐cyclopentanediones
Authors: Lazarević Zvjezdana , Vorkapić‐Furač Jasna , Tralić‐Kulenović Vesna
Published: May 2005

A study of the electron impact mass spectrometry is reported for eight, stable, previously synthesized, enolic isomers of 2‐aroyl‐4‐aracyl‐1,3‐cyclopentanediones.
Analysis of neuropeptides by perfusion liquid chromatography/electrospray ion‐trap mass spectrometry
Authors: Lin Hung‐Yu , Voyksner Robert D.
Published: May 2005

Perfusion high‐performance liquid chromatography (HPLC) combined with electrospray ion trap mass spectrometry (ITMS) was evaluated for the determination of neuropepetides in plasma. Perfusion HPLC offers the capability of resolving neuropeptides spiked into plasma in 5 min compared to the 30–60 min separations performed on packed capillary C18 columns. Electrospray combined with the ITMS provides the ability to ionize these neuropeptides and mass analyze them with high sensitivity and specificity. Sub‐picomole quantities of neuropeptides injected on‐column could be specifically detected in a plasma matrix. The electrospray‐ITMS mass spectrum of each neuropeptide showed multiply charged ions which could be used to determine or confirm their molecular weights.
The application of electrospray and neutral‐loss mass spectrometry to the identification of the metabolites of S12813 in rat liver slices
Authors: Brownsill Robin , Combal Jean‐Philippe , Taylor Albert , Bertrand Marc , Luijten Wim , Walther Bernard , Games D. E.
Published: May 2005

The metabolism of S12813, (3‐{2‐[4‐phenyl piperazin‐1‐yl] ethyl}‐2‐oxo‐2,3‐dihydro oxazolo [4, 5‐b] pyridine chlorohydrate), in rat liver slice incubates was examined by high performance liquid chromatography combined with mass spectrometry. Electrospray ionization was used together with tandem mass spectrometric techniques of analysis (MS/MS). Polar phase I and phase II metabolites were identified as C‐oxidation products, which were then conjugated to form either sulphate or glucuronide metabolites. On the basis of the identifications made, a metabolic pathway of S12813 in rat liver slices has been proposed.
Measurement of isotope effect on photodetachment cross‐sections of OH− and OD− by Fourier‐transform ion cyclotron resonance mass spectrometry
Authors: Naito Yasuhide , Ueno Hitoshi , Huramatsu Eiji , Inoue Masao
Published: May 2005

Isotope effect on photodetachment cross‐sections of OH− and OD− ions was studied using a Fourier‐transform ion cyclotron resonance mass spectrometer. The ions were produced by electron impact from a mixture of H2O and D2O gases, trapped in a cylindrical cell and irradiated by a 337 nm photon beam from a nitrogen pulsed laser. Intensities of both ions were measured simultaneously with and without irradiation. This allowed the determination of the ratio of the photodetachment cross‐sections of OH− and OD− ions without knowledge of the photon flux intensity and the geometrical overlap factor of laser beam and ion cloud in the cell. From the present result the difference in the equilibrium internuclear distances between OH− and OH was estimated as r(OH−) r(OH) ≈︁ −0.0074 Å.
Matrix‐assisted laser desorption/ionization: Dependence of the ion yield on the laser beam incidence angle
Authors: Westman Ann , Huth‐Fehre Thomas , Demirev Plamen , Bielawski Jacek , Medina Nelson , Sundqvist Bo U. R. , Karas M.
Published: May 2005

Some basic properties of matrix‐assisted laser desorption/ionization (MALDI) have been investigated by varying the angle between the pulsed UV‐laser beam and the target surface, thus determining its influence on the MALDI process. The minimum deposited laser energy needed for protein ion production (the threshold energy) and the protein‐yield dependence on the laser energy have been determined for incidence angles between 35° and 60° with respect to the target surface normal. The measurements demonstrate that neither the threshold energy nor the dependence of the protein yield on the laser energy vary with the incidence angle within the range studied. Hence the corresponding parameters that involve the area of irradiation, namely the threshold laser fluence as well as the ion‐yield dependence on fluence have a cosine dependence on the incidence angle. Furthermore, the threshold energy at constant incidence angle scales with the mass of the analyte molecule for proteins in the range from 5700 to 66 000 u.
Proton‐transfer reactions of mass‐selected multiply charged ions
Authors: Hunter Ann P. , Severs Joanne C. , Harris Frank M. , Games David E.
Published: May 2005

A triple‐quadrupole spectrometer has been used to study proton‐transfer reactions of multiply charged ions generated by electrospray ionization. Doubly and triply charged ions generated from the peptides Arg‐Lys‐Glu‐Val‐Tyr and Met‐Lys‐bradykinin, respectively, were found to undergo proton‐transfer reactions with ammonia molecules contained in the RF‐only quadrupole collision‐gas cell of the spectrometer. With horse‐heart myoglobin in the source, ions having charges of 20+, 19+, 16+ and 14+ were selected in turn by the first quadrupole and their proton‐transfer reactions with ammonia investigated. For each ion, numerous product ions were detected having charges (n‐1)+, (n‐2)+, (n‐3)+ … where n was the charge on the reacting parent ion. The possibility of using the experimental technique to measure approximately the proton affinities of multiply charged ions is discussed. Also, a procedure is outlined for identifying the charge states of product ions resulting from collision‐induced dissociation of multiply charged ions.
Interconversion of chemical species during analysis by gas chromatography/mass spectrometry
Authors: Monaghan John J. , Wagner Martin H.
Published: May 2005

The electron ionization mass spectra obtained, on two types of GC/MS instrument, of an impurity peak in a sample of fluorotrichloroethene (1) were those of two different compounds, viz., the epoxide of 1 and trichloroacetyl fluoride. Confirmation of the latter structure was provided by evidence from infrared spectroscopy. A study, on both instruments, of the variation of injector, source and interface temperatures has shown that the sample impurity is actually the epoxide which, at sufficiently high interface‐region temperatures, can be converted to the acyl fluoride species. Ab initio molecular orbital calculations have confirmed that the acyl fluoride is more stable than the epoxide.
Different mass spectrometric approaches in the identification of endogenous methylated purine bases in urine extracts
Authors: Porcelli Brunetta , Pagani Roberto , Lorenzini Luciano , De Martino Antonio , Catinella Silvia , Traldi Pietro
Published: May 2005

A preliminary identification of endogenous and exogenous methylated purine bases in urinary extracts of healthy and tumor‐bearing subjects has been performed using high performance liquid chromatography, and tandem mass spectrometry (MS/MS). MS/MS gave particularly fast and sensitive analyses, allowing the simultaneous and rapid determination of 26 different urinary methylated purines. Both sets of data confirm that tumor‐bearing patients show changed levels of methylated purine bases.
Tryptic peptide mapping of sequence 1–298 of human serum albumin by high‐performance liquid chromatography and fast‐atom bombardment mass spectrometry
Authors: Compagnini Anna , Fisichella Salvatore , Foti Salvatore , Saletti Rosaria , Sardo Letizia
Published: May 2005

The determination of the tryptic peptide mapping of sequence 1–298 of human serum albumin (HSA) by chemical and enzymatic cleavage and combined use of high‐performance liquid chromatography (HPLC) and fast‐atom bombardment mass spectrometry (FAB‐MS) is described. A total coverage of about 75% of the entire sequence was obtained. Unidentified fragments included some peptides which were not present in the chromatograms because of their extreme hydrophobic or hydrophilic character, as indicated by the calculated retention times. Due to the high reproducibility of the experiments and to the satisfactory yield of the tryptic fragments identified, the combined use of HPLC and FAB‐MS appears to possess great potential for structural investigation of HSA.
Carbon dioxide laser desorption/ionization mass spectrometry of a mixture of s‐triazine oligomers analyzed by a method which assumes a pattern of chemical formulae
Authors: Togashi Hisashi , Koga Yoshinori , Kakudate Yozo , Fujiwara Shuzo , Kubota Masaaki , Fukuda Kenzo , Nakagawa Hideki , Kawaguchi Masayuki
Published: May 2005

Mass spectra of intermediate products of polymer [(C3N3)2(NH)3]n were obtained by carbon dioxide laser desorption/ionization Fourier‐transform mass spectrometry and analyzed by a method which assumes the presence of a pattern of chemical formulae. It was found that a group of chemical formulae CxNyHz+ (4x‐3y+z=1) applies to most of the observed ions. These formulae were found to correspond to the ionic structures which are expected from a knowledge of reactions of s‐triazine derivatives.
The gas‐phase baker venkataraman rearrangement
Authors: Dua Suresh , Amemiya Sadaka , Bowie John H.
Published: May 2005

The condensed‐phase Baker Venkataraman rearrangement is an irreversible reaction, e.g. o‐(−CH2CO)C6H4OCOPh → o‐(−O)C6H4COCH2COPh. The collision‐induced mass spectra of these two ions show the corresponding gas‐phase reaction to be reversible.
Direct analysis of samples on paper by fast‐atom bombardment mass spectrometry
Authors: Zhongping Yao , Hanhui Wen , Qinming Zha , Weide He , Shankai Zhao
Published: May 2005

A method for obtaining fast‐atom bombardment mass spectra of samples on paper is described in which a scrap trimmed from the paper of interest is adhered to the FAB probe tip with a strip of double‐faced adhesive tape. After addition of suitable matrix (e.g. glycerol or thioglycerol) to the scrap, the probe is introduced into the mass spectrometer to obtain mass spectra in the usual manner. The method is demonstrated by analysing some paper containing hexadecyltrimethylammonium bromide, sodium dodecylbenzene sulfonate and vanillic acid. The method is also used to characterize paper chromatographic spots, by which the fractions of a mixture of three amino acids (L‐glutamic acid, L‐proline and L‐valine) separated by paper chromatography are easily determined. The detection limit of the method is well below 10 ng with respect to hexadecyltrimethylammonium bromide.
Collision‐induced dissociation mass spectrometry of the herbicide diclofop‐methyl
Authors: Headley John V. , Peru K. M. , Brooks Paul W.
Published: May 2005

The collision‐induced dissociation (CID) spectra of positive ions of the herbicide diclofop‐methyl are reported. The results indicate that for relatively low collision energies (⩽75eV, laboratory frame of reference), the distribution of the CID ions of the molecular ion correlates in a qualitative manner with the occurrence of transformation products arising from the degradation of the herbicide in geologic or biofilm materials. At low collision energies (30‐45 eV, laboratory frame of reference), the CID spectra contained a preponderance of product ions at m/z 281 and 253. These product ions correspond to prevalent transformation products in soil, 4‐(2,4‐dichlorophenoxy)dehydrophenetole (molecular ion 282) and 4‐(2,4‐dichlorophenoxy)phenol (molecular ion 254) respectively. At higher collision energies (⩾45eV), product ions were observed for up to three bond cleavages. The high energy CID product ions correspond to transformation products observed in mature biofilm materials cultivated on the parent herbicide as the sole carbon source.
Detection of nucleotide bases in ancient seeds using gas chromatography/mass spectrometry and gas chromatography/mass spectrometry/mass spectrometry
Authors: O'Donoghue Kerry , Brown Terence A. , Carter James F. , Evershed Richard P.
Published: May 2005

Nucleic acid extracts from 1400‐year‐old radish seeds recovered from excavations at Qasr Ibrim, Upper Egypt, have been analysed by gas chromatography/mass spectrometry and gas chromatography/mass spectrometry/mass spectrometry. tert‐Butyldimethyisilyl derivatives of the purine and pyrimidine bases were prepared, after treatment of the nucleic acid extracts with concentrated formic acid. Under electron ionization these derivatives yield prominent [M–57]+ ions that were found to be of value for use in analyses employing selected‐ion monitoring and product‐ion studies. These two techniques were used in the sensitive and selective detection of nucieotide bases in crude extracts of ancient seeds. The results obtained were supported by complementary analyses of hydrolysates of ancient nucleic acids and authentic bases by means of retention time and spectral comparisons. This work demonstrates for the first time that mass spectrometry can be used in the direct chemical examination of nucleotide bases in ancient materials. This analytical approach is currently being used to address questions regarding the possible chemical (diagenetic) changes occurring in the nucleic acids of ancient biological material.
The methyleneketene radical anion
Authors: Dua Suresh , Sheldon John C. , Bowie John H.
Published: May 2005

The methyleneketene radical anion is formed from Me3SiCOCHCH2. Deprotonation of this neutral by NH yields Me3SiCOC̄CH2 which then decomposes by loss of Me3Si· to yield CH2CCO−·. The identity of the product radical anion is determined by its charge‐reversal (positive ion) mass spectrum.
Effect of multiple sprayers on dynamic range and flow rate limitations in electrospray and ionspray mass spectrometry
Authors: Kostiainen Risto , Bruins Andries P.
Published: May 2005

The sample‐ion signal in electrospray mass spectrometry is an approximately linear function of sample concentration up to 10−5mol/L. Dynamic range for the tetrabutylammonium ion signal and spray current leaving the nebulizer are determined with one and two sprayers, at flow rates of 5 and 10 μL/min, and at different positions of the sprayer. The dynamic range does not appear to be limited by the total amount (mass) of sample, but by the concentration of the sample solution introduced into the ion source, as is demonstrated by the use of two parallel sprayers. Limitation of dynamic range as a result of increasing repulsion between charged droplets at higher sample concentration appears to be unlikely. The efficiency of droplet charging gradually decreases with increasing sample concentration, while the detector signal abruptly reaches a plateau. Limitation just by insufficient charge on droplets is ruled out. Limitation of sample‐ion signals can be attributed to an upper limit to the number of free quaternary ammonium ions at the surface of electrically charged droplets.

Multiple sprayers can be used to increase the range of flow rates accepted by the electrospray interface. In the case of ionspray (pneumatically assisted electrospray) the stability of the ion signal at higher flow rates is improved by the use of multiple sprayers.
Attomole detection of proteins by matrix‐assisted laser desorption/ionization mass spectrometry with the use of picolitre vials
Authors: Jespersen S. , Niessen W. M. A. , Tjaden U. R. , van der Greef J. , Litborn E. , Lindberg U. , Roeraade J. , Hillenkamp F.
Published: May 2005

Significant improvements in the absolute detection limits for proteins in matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) are demonstrated by the application of so‐called picolitre vials. By the reduction of the sample volume from a few μL down to 250 pL and simultaneous reduction of the sample spot area from a few mm2 down to 0.01 mm2, low attomole detection limits are obtained for bradykinin and cytochrome c. The detection limit in a single‐shot mass spectrum of bradykinin is estimated to be as low as 250 zeptomol. These are currently the lowest amounts of protein and the smallest volumes analyzed by MALDI‐MS.
Matrix‐assisted laser desorption mass spectrometry on a magnetic sector instrument fitted with an array detector
Authors: Bordoli Robert S. , Howes Kevin , Vickers Richard G. , Bateman Robert H. , Harvey David J. , Derrick P. J.
Published: May 2005

Matrix‐assisted laser desorption/ionization (MALDI) has been carried out on a high performance double‐focusing mass spectrometer fitted with an integrating focal plane array detector. High sensitivity (low femtomole detection) was obtained with peptides such as renin substrate. Underivatized complex oligosaccharides were also detectable at the 200 fmol level. The advantages of the array detector for improved resolution (5000 full width at half maximum) and the benefits in complex oligosaccharide and glycolipid analyses relative to MALDI time‐of‐flight (TOF) systems are shown. This improved resolution enabled ambiguities from the TOF data to be interpreted.
Microsecond pulsed glow discharge time‐of‐flight mass spectrometer
Authors: Hang Wei , Yang Pengyuan , Wang Xiaoru , Yang Chenglong , Su Yongxuan , Huang Benli
Published: May 2005

A linear time‐of‐flight mass spectrometer (TOFMS) has been designed, constructed, and coupled with a glow discharge source in microsecond pulsed mode (MSPGD). Orthogonal acceleration, a DC quadrupole and deflecting pulse techniques are used to diminish kinetic distribution and the spatial distribution of ions, and for deflecting Ar+ ions in their flight path. Comparison was made in the same discharge source between MSPGD and DC discharge. The continuous ion current is only 0.2 nA in the DC discharge mode, while the peak ion current reaches over 100 nA in the MSPGD mode. In addition, the ratio of the repelled ions to total ions is much higher in MSPGD than with a DC discharge in TOFMS. The mechanism of MSPGD is discussed. A resolving power of 500 was achieved, which is excellent for elemental analysis. To the authors' knowledge, this is the first time that a MSPGD‐TOFMS combination has been described. The system is now being further optimized to improve its performance.
On‐line buffer removal and fraction selection in gradient capillary high‐performance liquid chromatography prior to electrospray mass spectrometry of peptides and proteins
Authors: Roboz John , Yu Qitao , Meng Ankuo , Van Soest Remco , Aplin Robin
Published: May 2005

The technique for on‐line removal of buffers and for fraction selection to eliminate source clogging and suppression of electrospray ionization by unwanted constituents consisted of: (i) selecting the initial mobile phase composition to retain analytes on top of a capillary high‐performance liquid chromatography (HPLC) column; (ii) washing the buffer isocratically to waste, using a two‐way micro dump valve; (iii) starting the gradient and switching the dump valve to introduce analytes into the source. Peptide and protein mixtures were prepared in 0.05–0.5 M phosphate and 0.55 mM tris‐based buffers, and water. After buffer removal, chromatograms and electrospray spectra were indistinguishable from those of aqueous controls, down to 1 pmol (acidic fibroblast growth factor) consumed, and up to 78 kDa (bovine transferrin) molecular weight. Aided by the dump valve, 100 fmol of angiotensin could be fractionated and identified on the slope of a 10 × 106 fmol of leucine enkephalin HPLC peak. On‐line buffer removal and fraction selection eliminate the need for additional preparation steps than can lead to excessive sample losses.
Mass spectrometry of some imidazoles of pharmacological interest
Authors: Rizzi Emanuele , Ferrario Francesco , Sala Alberto , Catinella Silvia , Traldi Pietro
Published: May 2005

The electron‐impact induced fragmentation processes of nine differently N‐substituted imidazoles were studied by means of mass‐analyzed ion kinetic energy spectrometry. The compounds under study show a mass spectrometric behaviour different from that observed for other imidazoles already studied. In fact all the observed decompositions are related to the substituent chains.
Matrix‐assisted laser desorption/ionization capabilities in the study of non‐enzymatic protein glycation
Authors: Lapolla Annunziata , Fedele Domenico , Seraglia Roberta , Catinella Silvia , Traldi Pietro
Published: May 2005

Matrix‐assisted laser desorption/ionization mass spectrometry has been succesfully applied in the study of non‐enzymatic glycation of different proteins. In the case of bovine serum albumin, glycated by in vitro experiments performed under pseudophysiological conditions, a clear increase in molecular weight is observed with respect to both glucose concentrations and incubation time. The in vitro glycation of ribonuclease with glucose and fructose shows some peculiar differences either in terms of the number of condensed sugar molecules or in terms of the reaction kinetics. The same approach, applied to plasma proteins of healthy and diabetic subjects, provides evidence for the occurence of glycation of human serum albumin for the latter subjects.
Investigation of matrices for fast‐atom bombardment mass spectrometry of fullerenes
Authors: Zhongping Yao , Hanhui Wen , Qingmin Zha , Shankai Zhao
Published: May 2005

Phthalates (dimethyl, diethyl, dibutyl, diallyl and dinonyl) and p‐toluenesulfonates (methyl and ethyl) have been investigated as matrices for the fast‐atom bombardment mass spectrometric analysis of fullerenes for the first time. Compared with spectra obtained using 3‐nitrobenzyl alcohol and 2‐nitrophenyl octylether as matrices, the fast‐atom bombardment mass spectra of fullerenes with the two classes of compounds listed above as matrices are simple and show no fragment ions or adduct ions of fullerenes, and the matrices produce no background interference in the mass range of fullerenes.
Optimization by mass spectrometry of a tryptophan‐specific protein cleavage reaction
Authors: Vestling Martha M. , Kelly Michele A. , Fenselau Catherine , Costello Catherine E.
Published: May 2005

Mass spectrometry has been used to define the reaction of BNPS‐skatole (3‐bromo‐3‐methyl‐2‐(o‐nitrophenylsulfenyl)indolenine) with selected proteins and peptides, confirming the cleavage of the protein chain at tryptophan residues, characterizing the products, and identifying the side reactions. A short procedure for carrying out the cleavage reaction with minimal side reactions is presented.
Characterization of coal by matrix‐assisted laser desorption mass spectrometry. II. Pyrolysis tars and liquefaction extracts from the argonne coal samples
Authors: Herod Alan A. , Li Chun‐Zhu , Xu Bin , Parker John E. , Johnson Chris A. F. , John Phillip , Smith Gerry P. , Humphrey Paul , Chapman John R. , Kandiyoti Rafael , Games D. E.
Published: May 2005

Coal pyrolysis tars and liquefaction extracts prepared from the set of eight Argonne coal samples have been characterized by MALDI‐MS. A Kratos Kompact MALDI III linear time‐of‐flight mass spectrometer was used, with a nitrogen laser operating at 337 nm and sinapinic acid as matrix. Spectra were collected by summing 50 laser pulses at low laser fluence to avoid fragmentation of desorbed ions. At low mass, 200–500 u, spectra from the pyrolysis tars and liquefaction extracts showed common features: intense peaks originating from the sinapinic acid matrix, m/z 205, 224 and 246, and, a range of peaks in the mass range from about 250 u to 400 u, which probably corresponds to overlapping homologous series of apparently polar material. A peak of ion intensity between 1000 and 5000 u was systematically observed, which was sample dependent and not always similar for the tar and extract prepared from the same coal. At high masses, separate trends were observed for coal pyrolysis tars and liquefaction extracts: molar mass ranges of pyrolysis tars were smaller, and showed no particular trend with carbon content of the original coal; these findings are consistent with size‐exclusion chromatography derived findings. Spectra of liquefaction extracts extended over wider ranges of molar masses and increased with increasing coal rank; the highest masses extended to 50 000u. Overall, pyrolysis tars appeared structurally different from liquefaction extracts and more difficult to desorb. The effect of changes in laser fluence and ion extraction voltage on mass spectra have been investigated: high‐mass regions of the spectra were found to be very sensitive to the magnitude of the ion extraction voltage. No carbon clusters or fullerene structures were detected.
Sequence‐ion enhancement of peptides digested with proteinase K
Authors: Li Xiao‐Ling , Yang Hou‐Jun , Grotemeyer Jürgen
Published: May 2005

Proteinase K has been employed to proteolyze peptides before their mass spectrometric analysis. This combination of the two methods yields abundant sequence ions in the mass spectrum, thus leading to an easy prediction of the primary structure of the peptide. It was found that both the variety of available sequence ions and also their abundances are increased strongly after proteinase K digestion, when compared with the normal mass spectrum. The shortcoming of little fragmentation encountered using conventional mass spectrometric ionization methods can mostly be overcome. The H′n and Y"m ions produced from proteolysis provided a double check of the peptide sequence.
Isotopic fractionation in secondary ionization mass spectrometry
Authors: Lyon Ian C. , Saxton John M. , Turner Grenville , Hinton Richard
Published: May 2005

We have studied isotopic fractionation effects which occur during the analysis of oxygen isotope ratios by secondary ionization mass spectrometry. Variable instrumental isotopic fractionation has been well documented in the past as making reliable ion microprobe analyses of oxygen isotopes elusive. We report here techniques for minimizing these effects by careful optimization of an Isolab 54 ion microprobe and a method of integrating the secondary‐ion beam to eliminate a major source of fractionation caused by unequal focusing of isotopes on the source slit of the mass spectrometer. A further improvement has been the installation of new ion detectors for measuring 18O− and 17O− secondary ion beams in which the ions strike a conversion dynode (Conversion dynode system—CDS) to release electrons into a channeltron. The CDS detectors have a uniform, high and stable gain which, coupled with the beam integration techniques referred to above, yield reproducible oxygen isotope ratios on both conducting and insulating mineral standards (⩽1.2‰ on 18O/16O during a day and <2‰ over periods of days and weeks).
Electron ionization fragmentation of some isoindolone derivatives
Authors: Mäki Esa , Csende Ferenc , Stájer Géza , Vainiotalo Pirjo , Pihlaja Kalevi
Published: May 2005

The electron ionization mass spectra of eleven isoindolone derivatives are reported. The molecular ions of these compounds were stable, some of them even very abundant (8–29% of the total ion current). There were many ions common to all or most of the compounds studied, although the abundances varied markedly from case to case. The base peak varied also from compound to compound. The most important ions common to almost every compound were [M—(CH2)iXH]+ (ions ai; i=1–4), [M—C7H7]+ (ion b) and the ion pattern [c—H], c and [c + H] corresponding to the loss of fused carbocycle together with the carbonyl function. These ions are caused by α‐cleavages and inductive dissociations of the bonds of the molecular ion in respect to the hetero atoms X and/or N.
Does the observed mass in quadrupole mass filters operated under standard analytical conditions depend on isomeric ion structure?
Authors: Capron Laure , Rolando Christian , Sablier Michel
Published: May 2005

Recently published results have reported that mass displacements, which could reach 0.34 u, were observed in a quadrupole mass filter. An interaction between the dipole moment of ions and the quadrupolar RF field was then proposed to explain these mass displacements. We were interested by such an access to ion structure and decided to reproduce these results. Two sets of experiments were performed using two single‐stage quadrupole mass spectrometers operated under standard analytical conditions. Studies of the influence of resolution, source pressure and presence of helium or polar gas in the quadrupole enclosure on potential mass displacement detection have been performed. Nevertheless, we never observed significant mass shifts.
Chemical ionization mass spectra of linear alcohol polyethoxy carboxylates and polyethylene glycol dicarboxylates
Authors: Ding Wang‐Hsien , Fujita Yoshiko , Reinhard Martin
Published: May 2005

The chemical ionization (CI) mass spectra of propylated linear alcohol polyethoxy carboxylates (LAEC) and polyethylene glycol dicarboxylates (PEGDC) have been determined. Olefin displacement of the alkyl chain from the [M + H]+ ions of propylated LAEC formed the protonated polyethoxy carboxyl propyl ester, which then underwent a characteristic fragmentation by first losing water and then ethylene oxides. The fragmentation pattern for PEGDC [M + H]+ ions was similar to that of LAEC, except that the initial steps were displacement of one terminal propyl formate (HCOOC3H7) followed by a neutral loss of CH2O. Strong peaks due to protonated molecules were observed in both LAEC and PEGDC. Product‐ion mass spectra obtained from chemical ionization gas chromatographic/triple‐stage quadrupole mass spectrometric studies supported the proposed fragmentation mechanisms.
Matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry of DNA–Pt(II) complexes
Authors: Guittard J. , Pacifico C. , Blais J. C. , Bolbach G. , Chottard J. C. , Spassky A.
Published: May 2005

Matrix‐assisted laser desorption ionization (MALDI) time‐of‐flight mass spectrometry has been used to characterize the reaction products of the 18‐mer deoxyribonucleotide d(AACGGTTAACCGTTAATT) with [Pt(NH3)3(H2O)]2+ and cis‐[Pt(NH3)2(H2O)2]2+. Characteristic peaks corresponding to different monofunctional adducts {18‐mer+n[Pt(NH3)3]} (n =1, 2, 3 and 4) have been observed with the triamino–monoaqua complex. With the diamino‐diaqua cis‐Pt complex, formation of a chelate {18‐mer+[Pt(NH3)2]} involving two adjacent guanines has been demonstrated. A good correlation between MALDI and polyacrylamide gel electrophoresis results is observed.
Electron ionization mass spectrometry of 2‐halo ethanols
Authors: Carbini Massimo , Napoli Massimo , Gambaretto Giampaolo , Traldi Pietro
Published: May 2005

The mass spectrometric behaviour of 2‐fluoro, 2‐chloro, 2‐bromo and 2‐iodo ethanols has been studied in detail with the aid of metastable ion studies and deuterium labelling experiments. Clear differences are observed and rationalized in terms both of carbon–halogen bond strengths and electronegativity.
Mass spectral study of some new arylsulphonylamido‐thiophosphonamides
Authors: Nicoara Simona , Culea Monica , Palibroda Nicolae , Cozar Onuc , Fenesan Ioan , Hantz Andrei
Published: May 2005

This paper presents the interpretation of the mass spectra of some N′,N′‐dimethylamido‐cyclohexylthio phosphonic derivatives of the corresponding p‐R substituted N‐methyl arylsulphonamides, under electron impact. Normal mass spectra at 70 eV, metastable transition detection and accurate mass measurements were used to elucidate the ion fragmentation pathways.
Fragmentation processes of 1,2‐diphenoxyethane and 2‐phenoxyethanol by electron impact
Authors: Sekiguchi Osamu , Ayuzawa Terukazu , Fujishige Masao , Yanagisawa Tamae , Tajima Susumu
Published: May 2005

The unimolecular fragmentation processes of 1,2‐diphenoxyethane (1) and 2‐phenoxyethanol (2) upon electron impact were investigated by a combination of mass‐analyzed ion kinetic energy (MIKE) spectrometry, deuterium‐labelling, high resolution mass spectrometry, and kinetic energy release (KER) measurement. The MIKE spectrum and the KER measurement indicate that the predominant fragment ion at m/z 120 was generated from metastable 1+· ions via loss of a phenol molecule (C6H6O, 7), and that it has the same structure as the molecular ion of 2,3‐dihydrobenzofuran (C8H8O, 3). The metastable 2+· ion eliminates C2H4O and C2H3O to produce product ions at m/z 94 (C6H6O+·, 7+·) and 95 (C6H7O+) with single and double hydrogen atom transfer, respectively. These reactions occur through some complex rearrangement reactions.
A new method for the rapid deconvolution of partially resolved spectra
Authors: Brenton A. Gareth , Lock Christopher M.
Published: May 2005

A rapid and simple method for deconvolution of partially resolved spectra has been developed. The algorithm is simple, extremely fast, and capable of deconvolving whole spectra in real time on a fast personal computer. The technique has been evaluated using known test spectra whose resolution has been purposely degraded. The original spectra were reproduced accurately, both in the positions and the intensities of the individual peaks they contained. The method was initially developed for translational energy spectroscopy (TES), where there is little a priori information on the spacing and widths of individual peaks in a spectrum. Examples are given for actual experimental TES spectra of varying complexity and signal‐to‐noise ratios. Four key variables are required as input before the programme can be executed; these have been parameterized for a range of conditions and typical values have been established. The procedure may be well suited as a rapid pre‐screening process before more elaborate techniques are used and it can be applied widely, for example to deconvolute electrospray mass spectra.
A study of reduction phenomena in a high performance liquid chromatography/particle beam/mass spectrometer system
Authors: Xiao He , Brindle Ian D. , Jones Timothy R. B. , Miller Jack M. , Singh Raj P.
Published: May 2005

In this paper we report our studies of reduction phenomena in a high performance liquid chromatography/particle beam interface‐mass spectrometer system (HPLC/PB‐MS). It is shown that reduction takes place in the ion source of the mass spectrometer, but that the particle beam interface plays an important role in the reduction process since the HPLC mobile phase is involved in the reduction. HPLC flow rate and desolvation‐chamber temperature have significant effects on the reduction extent, while ion‐source temperature has only a minor effect. All the nitro compounds and sulfoxides tested in this work showed reduction in the system. There was no observed reduction for sulfones. 1,4‐Naphthaquinone showed significant reduction, while no reduction was observed for anthraqunone.