bluuebunny/crossref_metadata_2025_split huggingface dataset:
Initial implementation of external accumulation liquid chromatography/electrospray ionization Fourier transform ion cyclotron resonance with automated gain control
Authors: Belov Mikhail E. , Rakov Vsevolod S. , Nikolaev Eugene N. , Goshe Michael B. , Anderson Gordon A. , Smith Richard D. 
Published: March 2003

AbstractCapillary liquid chromatography (LC) separation coupled with external accumulation Fourier transform ion cyclotron resonance (FTICR) mass spectrometry has recently been demonstrated to have significant potential for proteomics research. Accumulation of an excessive space charge external to the FTICR cell ion trap has been shown to result in increased mass measurement error, undesirable ion discrimination and/or fragmentation, potentially causing misrepresentation or incorrect assignments of lower abundance peptides in the acquired mass spectra. In this work we report on the capability of data‐dependent adjustment of ion accumulation times in the course of LC separations, further referred to as automated gain control (AGC). Three different AGC approaches were evaluated based on the number of putative peptides from a tryptic digest of four casein proteins detected in the course of LC/FTICR separations. When compared with the conventional technique, AGC was found to increase, up to a factor of 3, the total number of peptides identified. Copyright © 2003 John Wiley & Sons, Ltd.
The shielding effect of glycerol against protein ionization in electrospray mass spectrometry
Authors: Mendes Maria Anita , Chies Jocelei Maria , Dias Ana Christina de Oliveira , Filho Spartacos Astofi , Palma Mario Sergio 
Published: March 2003

AbstractMost commercial recombinant proteins used as molecular biology tools, as well as many academically made preparations, are generally maintained in the presence of high glycerol concentrations after purification to maintain their biological activity. The present study shows that larger proteins containing high concentrations of glycerol are not amenable to analysis using conventional electrospray ionization mass spectrometry (ESI‐MS) interfaces. In this investigation the presence of 25% (v/v) glycerol suppressed the signals of Taq DNA polymerase molecules, while 1% (v/v) glycerol suppressed the signal of horse heart myoglobin. The signal suppression was probably caused by the interaction of glycerol molecules with the proteins to create a shielding effect that prevents the ionization of the basic and/or acidic groups in the amino acid side chains. To overcome this difficulty the glycerol concentration was decreased to 5% (v/v) by dialyzing the Taq polymerase solution against water, and the cone voltage in the ESI triple‐quadrupole mass spectrometer was set at 80–130 V. This permitted observation of a mass spectrum that contained ions corresponding to protonation of up to 50% of the ionizable basic groups. In the absence of glycerol up to 85% of the basic groups of Taq polymerase became ionized, as observed in the mass spectrum at relatively low cone voltages. An explanation of these and other observations is proposed, based on strong interactions between the protein molecules and glycerol. For purposes of comparison similar experiments were performed on myoglobin, a small protein with 21 basic groups, whose ionization was apparently suppressed in the presence of 1% (v/v) glycerol, since no mass spectrum could be obtained even at high cone voltages. Copyright © 2003 John Wiley & Sons, Ltd.
Analysis of native and chemically modified oligonucleotides by tandem ion‐pair reversed‐phase high‐performance liquid chromatography/electrospray ionization mass spectrometry
Authors: Fountain Kenneth J. , Gilar Martin , Gebler John C. 
Published: March 2003

AbstractIon‐pair reversed‐phase high‐performance liquid chromatography (IP‐RP‐HPLC) was utilized in tandem with negative‐ion electrospray ionization time‐of‐flight mass spectrometry (ESI‐TOFMS) for the analysis of native and chemically modified oligonucleotides. Separation was performed on a 1.0 × 50 mm column packed with porous C18 sorbent with a particle size of 2.5 μm and an average pore diameter of 140 Å. A method was developed which maximizes both chromatographic separation and mass spectrometric sensitivity using an optimized buffer system containing triethylamine and 1,1,1,3,3,3‐hexafluoro‐2‐propanol with a methanol gradient. The ESI‐TOFMS tuning parameters were also optimized in order to minimize in‐source fragmentation and achieve the best sensitivity. Analyses of native, phosphorothioate, and guanine‐rich oligonucleotides were performed by LC/MS. Detection limits were at sub‐picomole levels with an average mass accuracy of 125 ppm. The described method allowed for the LC/MS analysis of oligonucleotides up to 110mer in length with little alkali cation adduction. Since sensitive detection of oligonucleotides was achieved with ultraviolet (UV) detection, we utilized a combination of UV‐MS for quantitation (UV) and characterization (MS) of oligonucleotides and their failure sequence fragments/metabolites. Copyright © 2003 John Wiley & Sons, Ltd.
Determination of patterns of biologically relevant aldehydes in exhaled breath condensate of healthy subjects by liquid chromatography/atmospheric chemical ionization tandem mass spectrometry
Authors: Andreoli Roberta , Manini Paola , Corradi Massimo , Mutti Antonio , Niessen Wilfried M. A. 
Published: March 2003

AbstractA method for the simultaneous determination of several classes of aldehydes in exhaled breath condensate (EBC) was developed using liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry (LC/APCI‐MS/MS). EBC is a biological matrix obtained by a relatively new, simple and noninvasive technique and provides an indirect assessment of pulmonary status. The measurement of aldehydes in EBC represents a biomarker of the effect of oxidative stress caused by smoke, disease, or strong oxidants like ozone. Malondialdehyde (MDA), acrolein, α,β‐unsaturated hydroxylated aldehydes [namely 4‐hydroxyhexenal (4‐HHE) and 4‐hydroxynonenal (4‐HNE)], and saturated aldehydes (n‐hexanal, n‐heptanal and n‐nonanal) were measured in EBC after derivatization with 2,4‐dinitrophenylhydrazine (DNPH). Atmospheric pressure chemical ionization of the analytes was obtained in positive‐ion mode for MDA, and in negative‐ion mode for acrolein, 4‐HHE, 4‐HNE, and saturated aldehydes. DNPH derivatives were separated on a C18 column using variable proportions of 20 mM aqueous acetic acid and methanol. Linearity was established over 4–5 orders of magnitude and limits of detection were in the 0.3–1.0 nM range. Intra‐day and inter‐day precision were in the 1.3–9.9% range for all the compounds. MDA, acrolein and n‐alkanals were detectable in all EBC samples, whereas the highly reactive 4‐HHE and 4‐HNE were found in only a few samples. Statistically significant higher concentrations of MDA, acrolein and n‐hexanal were found in EBC from smokers. Copyright © 2003 John Wiley & Sons, Ltd.
Evaluation of a new multiple‐layer spotting technique for matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry of synthetic polymers
Authors: Meier Michael A. R. , Schubert Ulrich S. 
Published: March 2003

AbstractA new multiple‐layer matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS) sample‐spotting technique is described. This fast and easy technique was evaluated with poly(ethylene glycol) (PEG) standards and optimized conditions for these synthetic polymers were obtained. PEGs up to 35 kDa were detectable with this approach and single monomer resolution was observed up to 20 kDa. The spotting was performed using a multiple‐layer approach, which offers the capability of complex sample preparation without the requirement of premixing the different matrix, analyte and doping salt solutions. The technique reduces the time required for sample preparation and offers high flexibility with respect to sample composition and solvents utilized for the crystallization of the compounds. The technique is thus perfectly suited for applications in combinatorial material research. Copyright © 2003 John Wiley & Sons, Ltd.
Mass spectral studies of N,N‐dialkylaminoethanols
Authors: Reddy T. Jagadeshwar , Mirza Shama P. , Saradhi U. V. R. Vijaya , Rao V. Jayathirtha , Vairamani M. 
Published: March 2003

AbstractSome dialkylaminoethanols, precursors of chemical warfare agents such as V‐agents and nitrogen mustards, were analyzed by electron impact (EI) and electrospray ionization (ESI) mass spectrometry. The fragmentation pathways in EI and ESI‐MS/MS methods are rationalized. The collision‐induced dissociation (CID) spectra of [M+H]+ ions of aminoethanols in ESI mode are clearly distinguishable from one another, including those of isomeric normal and branched chain dialkylaminoethanols. Structures can be proposed based on the general fragmentation pathways of these molecules. Copyright © 2003 John Wiley & Sons, Ltd.
Nitrogen purity influences the occurrence of As+ ions in high‐performance liquid chromatography/electrospray ionization mass spectrometric analysis of four common arsenosugars
Authors: Kuehnelt Doris , Goessler Walter , Francesconi Kevin A. 
Published: March 2003

AbstractHigh‐performance liquid chromatography coupled to electrospray ionization mass spectrometry (HPLC/ESI‐MS) can provide both elemental and molecular information and, therefore, is a very useful tool for the identification of arsenic compounds. When a method for the identification of four arsenosugars was employed in our laboratory with an HPLC/ESI‐MS system equipped with a Whatman model 75‐72 nitrogen generator, a signal at m/z 75 (As+) could not be observed. When the HPLC/ESI‐MS system was operated with nitrogen 5.0 (nitrogen of a purity of at least 99.999%) all four arsenosugars gave a signal at m/z 75. Because of this observation the influence of the quality of the nitrogen drying gas on the fragmentation of the four arsenosugars was systematically investigated. Standard solutions containing the four arsenosugars (0.5 ng As each) were separated on an anion‐exchange column and detected with ESI‐MS in the positive ion mode by monitoring the signals for [M+H]+, m/z 237, 91, and 75. Nitrogen with defined oxygen concentrations was used as drying gas. The purity of the nitrogen ranged from 99 to 99.999% (10 400 to 10 ppm oxygen impurity). The nitrogen with 99% purity gave no signal at m/z 75, but signals were obtained at m/z 91, 237, and for [M+H]+. When higher purity nitrogen (99.9%) was used, a signal was obtained at m/z 75, which accounted for 0.8–1.1% (depending on the kind of arsenosugar) of the sum of the signals for m/z 75, 91, 237 and [M+H]+. As the level of oxygen in the nitrogen decreased, the m/z 75 signal increased to 2.0–3.1%. This was accompanied by a concomitant decrease in the m/z 91 signal from 5.2–6.6% to 0.7–1.5%, whereas the signals for [M+H]+ and m/z 237 were essentially unchanged. Signals at m/z 75 with intensities comparable with those observed for the 99.9% pure nitrogen were also obtained for all the arsenosugars when the HPLC/ESI‐MS system was operated with a Domnick Hunter Nitrox UHPLCMS18 nitrogen generator. Dimethylarsinic acid, arsenobetaine, trimethylarsine oxide, arsenocholine and the tetramethylarsonium cation also gave no signal at m/z 75 when they were analyzed with the Whatman model 75‐72 nitrogen generator, but clear signals at m/z 75 were observed with the Domnick Hunter Nitrox UHPLCMS18 nitrogen generator. A nitrogen quality of at least 99.9% is required to obtain elemental information (m/z 75) when arsenic compounds are investigated by HPLC/ESI‐MS. Molecular and elemental information from one chromatographic run is a valuable tool for the characterization of unknown arsenic compounds. Copyright © 2003 John Wiley & Sons, Ltd.
Confirmatory analysis of β‐lactam antibiotics in kidney tissue by liquid chromatography/electrospray ionization selective reaction monitoring ion trap tandem mass spectrometry
Authors: Fagerquist Clifton K. , Lightfield Alan R. 
Published: March 2003

AbstractEleven β‐lactam antibiotics were analyzed in fortified and incurred beef kidney tissue using high‐performance liquid chromatography/electrospray ionization/selective reaction monitoring‐ion trap tandem mass spectrometry (LC/ESI‐SRM‐MSn). The analytes included: deacetylcephapirin, amoxicillin, cephapirin, desfuroylceftiofur cysteine disulfide (DCCD, a biomarker of ceftiofur), ampicillin, cefazolin, Pen G, oxacillin, cloxacillin, naficillin and dicloxicillin. Analytes were extracted with acetonitrile and water. Clean‐up was performed by solid‐phase extraction. Limits of confirmation in fortified tissue are as follows (tolerances or target levels in parentheses): deacetylcephapirin: 10–50 ng/g (100 ng/g); amoxacillin: 50–100 ng/g (10 ng/g); cephapirin: 10 ng/g (100 ng/g); DCCD: 500 ng/g (8000 ng/g); ampicillin: 10 ng/g (10 ng/g); cefazolin: 10 ng/g (10–50 ng/g); Pen G: 10 ng/g (50 ng/g); oxacillin: 10 ng/g (10–50 ng/g); cloxacillin: 10 ng/g (10 ng/g); naficillin: 10 ng/g (10–50 ng/g); dicloxacillin: 100–500 ng/g (10–50 ng/g). The present method was also tested on incurred kidney tissue that had previously been analyzed using a microbial assay. Good correspondence was found between the results from this new method and the bioassay. However, the present method is much more specific and, in several cases, more sensitive than the bioassay. In addition, the time of analysis is significantly shorter than the bioassay. We also found that SRM MSn was superior in the analysis of unknown incurred tissue than full spectrum MSn. We also obtained an MS/MS spectrum of DCCD that is significantly at variance with previously published fragmentation spectra. Published in 2003 by John Wiley & Sons, Ltd.
Detection of inorganic species by chemical reaction laser desorption ionization mass spectrometry
Authors: Matsumoto Kozo , Ajiro Hiroharu , Habaue Shigeki , Okamoto Yoshio 
Published: March 2003

AbstractThe oxidation numbers of metals in inorganic compounds were identified by matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) by using their acetylacetonates, which are soluble in acetone. For the MALDI analysis of inorganic species insoluble in common solvents used for matrices, such as acetone, methanol, water, etc., a suspension method of sample preparation was developed. Turbid suspensions of inorganic species in the solvent were spotted on the sample holder with chelating reagents, as in the conventional sample preparation for MALDI‐MS. Chemical reaction between the inorganic species and the chelating reagents occurred in the plume after irradiation by laser light. Metal oxides were also analyzed by this method, and samples with different oxidation numbers gave different mass spectra. These results suggest that many other metal oxides with different oxidation numbers could be identified if suitable chelating reagents are chosen for sample preparation for MALDI‐MS. Copyright © 2003 John Wiley & Sons, Ltd.
Stable isotope dilution method for the determination of guanidinoacetic acid by gas chromatography/mass spectrometry
Authors: Fingerhut Ralph 
Published: March 2003

AbstractFor more than 30 years, guanidinoacetic acid (GAA), together with other guanidino compounds, has been proposed as an important marker for renal failure, in kidney transplantation, and for renal metabolism, especially for the metabolic activity of the renal proximal tubules. Since the discovery of the first patient with guanidinoacetic acid methyltransferase deficiency in 1994 by Stöckler et al. (Pediatr. Res. 1994; 36: 409), GAA has become of great interest for all laboratories involved in the diagnosis of metabolic diseases. In the literature there are several methods described for the determination of GAA, ranging from ion‐exchange chromatography with post‐column derivatisation, enzymatic methods, gas chromatography/mass spectrometry (GC/MS), to liquid chromatography/atmospheric pressure chemical ionisation mass spectrometry (LC/APCI‐MS). Here a stable isotope dilution method for quantitative and accurate determination of GAA in urine, plasma, and cerebrospinal fluid is described. GAA is converted to the bis(trifluoromethyl)pyrimidine di(tert‐butyldimethylsilyl) derivative by stepwise derivatisation with hexafluoroacetylacetone and N‐(tert‐butyldimethylsilyl)‐N‐methyltrifluoroacetamide (MTBSTFA). Analysis can be performed using a standard benchtop GC/MS system. For quantitative GAA determination with 1,2‐13C‐GAA as internal standard, selected ion monitoring is performed using m/z 460/462, with m/z 432/433 and 375/376 as qualifiers. Copyright © 2003 John Wiley & Sons, Ltd.
Analysis of class I phosphoinositide 3‐kinase autophosphorylation sites by mass spectrometry
Authors: Czupalla Cornelia , Nürnberg Bernd , Krause Eberhard 
Published: March 2003

AbstractThis article describes the identification of the autophosphorylation sites of the G protein‐sensitive class I phosphoinositide 3‐kinase isoforms β and γ by mass spectrometry. Since discrimination and suppression effects prevented the immediate detection and sequencing of phosphopeptides in complex mixtures, a strategy was applied that involved 32P‐radiolabeling of the phosphoproteins, cleavage of the phosphoproteins with several proteases and/or cyanogen bromide, separation of the resulting peptide mixtures by micro‐reversed‐phase liquid chromatography, and mass spectrometric analysis of fractions containing phosphopeptides. As a result the primary autophosphorylation sites of phosphoinositide 3‐kinase p110β and p110γ subunits could be unambiguously assigned to the C‐terminal Ser 1070 and Ser 1101, respectively. Copyright © 2003 John Wiley & Sons, Ltd.
Nitrogen isotopomer site preference of N2O produced by Nitrosomonas europaea and Methylococcus capsulatus Bath
Authors: Sutka R. L. , Ostrom N. E. , Ostrom P. H. , Gandhi H. , Breznak J. A. 
Published: March 2003

AbstractThe relative importance of individual microbial pathways in nitrous oxide (N2O) production is not well known. The intramolecular distribution of 15N in N2O provides a basis for distinguishing biological pathways. Concentrated cell suspensions of Methylococcus capsulatus Bath and Nitrosomonas europaea were used to investigate the site preference of N2O by microbial processes during nitrification. The average site preference of N2O formed during hydroxylamine oxidation by M. capsulatus Bath (5.5 ± 3.5‰) and N. europaea (−2.3 ± 1.9‰) and nitrite reduction by N. europaea (–8.3 ± 3.6‰) differed significantly (ANOVA, f(2,35) = 247.9, p = 0). These results demonstrate that the mechanisms for hydroxylamine oxidation are distinct in M. capsulatus Bath and N. europaea. The average δ18O‐N2O values of N2O formed during hydroxylamine oxidation for M. capsulatus Bath (53.1 ± 2.9‰) and N. europaea (−23.4 ± 7.2‰) and nitrite reduction by N. europaea (4.6 ± 1.4‰) were significantly different (ANOVA, f(2,35) = 279.98, p = 0). Although the nitrogen isotope value of the substrate, hydroxylamine, was similar in both cultures, the observed fractionation (Δ15N) associated with N2O production via hydroxylamine oxidation by M. capsulatus Bath and N. europaea (−2.3 and 26.0‰, respectively) provided evidence that differences in isotopic fractionation were associated with these two organisms. The site preferences in this study are the first measured values for isolated microbial processes. The differences in site preference are significant and indicate that isotopomers provide a basis for apportioning biological processes producing N2O. Copyright © 2003 John Wiley & Sons, Ltd.
Generation and reactions of substituted phenide anions in an electrospray triple quadrupole mass spectrometer
Authors: Bieńkowski Tomasz , Danikiewicz Witold 
Published: March 2003

AbstractSubstituted benzoic acid anions undergo decarboxylation in the medium‐pressure region of an electrospray ion source yielding in most cases the correspondingly substituted phenide anions in high yield. The location of the anionic center is specified by the position of the carboxylic group. The only exceptions are compounds with substituents containing acidic hydrogen atoms, like OH and NH2 groups. For such compounds, either an intra‐ or an intermolecular (mediated by the molecules of methanol or water) proton transfer from the more acidic position to the benzene ring is observed. The generated anions can be selected using the first quadrupole for studying their ion‐molecule chemistry in the second quadrupole of a triple quadrupole mass spectrometer. Their reactions with CO2, O2, CH3COCH3 and CCl4 may serve as typical examples. The general applicability of this method for the generation of phenide anions has been confirmed on three different mass spectrometers. Experiments performed using carboxylic acids other then benzoic acid and its derivatives show that this method is not limited to phenide anions and can be used for the generation of a much wider range of carbanions in the gas phase. Copyright © 2003 John Wiley & Sons, Ltd.
Determination of α‐tocopherol in infant foods by liquid chromatography combined with atmospheric pressure chemical ionisation mass spectrometry
Authors: Kalman Andras , Mujahid Claudia , Mottier Pascal , Heudi Olivier 
Published: March 2003

AbstractA novel, sensitive and specific method for the quantification of α‐tocopherol in two infant foods (milk and cereals) using liquid chromatography on‐line with positive atmospheric pressure chemical ionisation mass spectrometry detection (LC/APCI‐MS) has been developed. The samples were first saponified in order to eliminate fats and to transform tocopherol esters into free tocopherol, followed up by a liquid–liquid extraction of the analyte in petroleum benzine/diisopropyl ether (75:25, v/v) prior to injection onto the LC system. For the quantification, deuterium‐labelled tocopherol was used as internal standard and the samples were monitored in selected ion monitoring (SIM) mode. Calibration curves between 1–40 μg/mL of α‐tocopherol showed a good linear correlation (r2 = 0.99994), and the detection limit was determined to be 2.5 ng/mL. The within‐day and between‐day precision were determined for several dietetic infant formulae and certified reference samples, and found to be below 3.5%. The accuracy determined on a Nestlé reference sample (milk powder) was calculated to be 115.2 ± 1.2%, which confirms the robustness of the proposed method. This study shows that single quadrupole LC/MS can be applied for the quantification of vitamins in food and the method offers better sensitivity and selectivity than traditional method such as LC‐UV. This would simplify the preparation of the food samples and consequently enhance the vitamin analysis throughput in the food area. Copyright © 2003 John Wiley & Sons, Ltd.