bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of a correction to improve mass measurement accuracy of isotopically unresolved polymerase chain reaction amplicons by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry
Authors: Null Allison P. , Muddiman David C.
Published: July 2003

The experimental determination of average mass by mass spectrometry is limited for large molecules due to the negative bias introduced by the natural distribution of isotopic abundances. This results in the measurement of the top‐of‐centroid (ToC) as opposed to the true centroid. We have developed a practical correction factor that is applied to the ToC measurement to largely remove the systematic bias introduced by nature. The correction factor is calculated easily using the average molecular mass (<100 kDa) of the analyte molecule and the full‐width half maximum resolving power (<3500) of the measurement. In addition, an approach to calculating resolving power is described that accurately predicts resolving power achievable for Fourier transform ion cyclotron resonance (FT‐ICR) mass analysis of large molecules. A combination of internal calibration with a dual‐electrospray source and application of the correction factor to average mass measurements improved the mass error from 192.5 to −35.0 ppm for a 44 kDa PCR amplicon. Copyright © 2003 John Wiley & Sons, Ltd.
Preliminary investigation of the simultaneous detection of sugars, ascorbic acid, citric acid, and sodium benzoate in non‐alcoholic beverages by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry
Authors: Ayorinde Folahan O. , Bezabeh Dawit Z. , Delves I. G.
Published: July 2003

Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS) was used for the simultaneous detection of sugars, ascorbic acid, citric acid, sodium and/or potassium benzoate in non‐alcoholic beverages, with meso‐tetrakis(pentafluorophenyl)porphyrin (MW 974) as a matrix. Using potassium hydroxide as dopant, fructose/glucose was detected as the potassiated molecule at m/z 219, whereas potassiated sucrose, [Sucrose · K]+, was detected at m/z 381. Using sodium hydroxide as dopant, the fructose and sucrose ions were detected at m/z 203 and 365, respectively. Citric acid generated multiple ions at m/z 269, 307, and 345, which were assigned to [CitricH+2K]+, [Citric2H+3K]+, and [Citric3H+4K]+, respectively. However, a stored methanolic solution of citric acid produced additional ions at m/z 283, 297, and 321, which were attributed to [Citric2H+CH3+2K]+, [Citric3H+2CH3+2K]+, and [Citric3H+CH3+3K]+, respectively, due to esterification that took place during storage. The limits of detection in water were: ascorbic acid, 0.30 wt%; citric acid, 0.5 wt%; and sodium benzoate, 0.001 wt%. In the beverage formulations, the limits of detection were: ascorbic acid 0.3 wt%, citric acid 0.3 wt%, and sodium benzoate 0.02 wt%. Spiking a water or beverage solution that contained ascorbic and/or citric acid with less than 0.6 wt% of tartaric acid lowered the detection limits of ascorbic and citric acids to 0.2 wt%. This study demonstrates the potential for using MALDI‐TOFMS in the quality control analyses of non‐alcoholic beverages, particularly with regard to the detection of low molecular weight organic acids in commercial beverage formulations. Copyright © 2003 John Wiley & Sons, Ltd.
Matrix‐assisted laser desorption/ionization directed nano‐electrospray ionization tandem mass spectrometric analysis for protein identification
Authors: Kast Juergen , Parker Carol E. , van der Drift Koen , Dial J. Michael , Milgram Sharon L. , Wilm Matthias , Howell Michael , Borchers Christoph H.
Published: July 2003

In those cases where the information obtained by peptide mass fingerprinting or matrix‐assisted laser desorption/ionization tandem mass spectrometry (MALDI‐MS/MS) is not sufficient for unambiguous protein identification, nano‐electrospray ionization (nano‐ESI) and/or electrospray ionization tandem mass spectrometry (ESI‐MS/MS) analysis must be performed. The sensitivity of nano‐ESI/MS, however, is lower than that of MALDI‐MS, especially at very low analyte concentrations and/or in the presence of contaminants, such as salt and detergents. Moreover, to perform ESI‐MS/MS, the peptide masses of the precursor ions must be known. The approach described in this paper, MALDI‐directed nano‐ESI‐MS/MS, makes use of information obtained from the more sensitive MALDI‐MS experiments in order to direct subsequent nano‐ESI‐MS/MS experiments. Peptide molecular ions found in the MALDI‐MS analysis are then selected, as their (+2) precursor ions, for nano‐ESI‐MS/MS sequencing, even though these ions cannot be detected in the ESI‐MS spectra. This method, originally proposed by Tempst et al. (Anal. Chem. 2000, 72: 777–790), has been extended to provide better sensitivity and shorter analysis times; also, a comparison with liquid chromatography/tandem mass spectrometry (LC/MS/MS) has been performed. These experiments, performed using quadrupole time‐of‐flight instruments equipped with commercially available nano‐ESI sources, have allowed the unambiguous identification of in‐gel digested proteins at levels below their ESI‐MS detection limits, even in the presence of salts and detergents. Copyright © 2003 John Wiley & Sons, Ltd.
Reactions between M+ (M = Si, Ge, Sn and Pb) and benzene in the gas phase
Authors: Xing Xiaopeng , Tian Zhixin , Liu Hongtao , Tang Zichao
Published: July 2003

Using a laser ablation/inert buffer gas ion source coupled with a reflectron time‐of‐flight mass spectrometer, the gas‐phase reactions between the IVA group element ions M+ (M = Si, Ge, Sn and Pb) and benzene seeded in argon gas were studied. In addition to the association reaction pathway (forming [M(C6H6)x]+, x = 1, 2, etc.), benzene was dissociated to form complex ions [M(C5H5)]+, [M(C7H5)]+ and [M(C9Hx)]+ (x = 5, 7 and 9), etc. DFT theoretical calculations indicated that, in the association products [M(C6H6)]+, the M atom is close to one carbon atom of benzene, while in most of the dissociation complexes, pentagonal structures (M/cyclopentadienyl derivatives) were formed, with the M atom situated near the fivefold axis of the five‐membered ring. The bond patterns in these complexes are discussed. Copyright © 2003 John Wiley & Sons, Ltd.
Hemoglobin adducts from glycidamide: acetonization of hydrophilic groups for reproducible gas chromatography/tandem mass spectrometric analysis
Authors: Paulsson Birgit , Athanassiadis Ioannis , Rydberg Per , Törnqvist Margareta
Published: July 2003

Acrylamide (AA) is a reactive compound widely used as an industrial chemical. It is also, as recently shown, present in heated foodstuffs. AA is known to cause tumors in rodents and is classified as probably carcinogenic to humans. The metabolite glycidamide (GA) is assumed to be the predominant genotoxic agent in AA exposure. Therefore, knowledge about in vivo doses of GA is essential for cancer risk assessment of exposure to AA. The in vivo dose of GA could be inferred from the level of the adduct formed by GA with N‐terminal valine (GA‐Val) in hemoglobin (Hb), detached as a pentafluorophenylthiohydantoin (PFPTH) and measured by gas chromatography/tandem mass spectrometric (GC/MS/MS) analysis. However, due to the highly polar character of the GA‐Val‐PFPTH derivative, it was found necessary to modify the method through further derivatization. This paper presents an evaluation of acetonization for derivatization of the adjacent OH and NH2 groups in the adduct formed from GA. Good reproducibility was obtained. Also, acetonization improves the response and thus increases the sensitivity of the GC/MS/MS analysis of the PFPTH derivative of GA‐Val. The sensitivity obtained is sufficient for studies of background adduct levels of GA in animals and in humans. Acetonization as a method for derivatization is robust and simple. Copyright © 2003 John Wiley & Sons, Ltd.
Particle beam glow discharge mass spectrometry: spectral characteristics of nucleobases
Authors: Davis W. Clay , Venzie Jacob L. , Willis Bert , Coffee R. Lane , Arya Dev P. , Marcus R. Kenneth
Published: July 2003

Use of a particle beam glow discharge (PB‐GD) source for mass spectrometric determinations of deoxy‐ and ribonucleosides and nucleotides is described. Use of this combination of sample introduction and ion source decouples the vaporization and ionization steps, leading to very simple spectral structure. The mass spectra of these compounds are EI‐like in nature, with clearly identified molecular ions and fragmentation patterns that are easily rationalized. The PB‐GDMS combination can be operated in a flow injection mode wherein the analyte is injected directly into the solvent flow, or can also be coupled to a high‐performance liquid chromatography (HPLC) system allowing LC/MS analysis of mixtures. Mass spectra obtained for nucleic acid bases, nucleosides, and nucleotides are readily obtained with injections of low‐nanomole quantities. Representative PB‐GDMS spectra for deoxy‐ and ribonucleosides, nucleotides, and mixed‐base oligonucleotides are presented to demonstrate the capabilities of the GD source. Characteristic fragmentation peaks from the spectra of adenine, cytosine, guanine, and thymine were identified in 22‐base sequences of single‐stranded DNA. The PB‐GD source is capable of producing spectra that may be used to identify the individual bases present in mixed‐base DNA and RNA fragments. Copyright © 2003 John Wiley & Sons, Ltd.
Combined infrared multiphoton dissociation and electron capture dissociation with a hollow electron beam in Fourier transform ion cyclotron resonance mass spectrometry
Authors: Tsybin Youri O. , Witt Matthias , Baykut Gökhan , Kjeldsen Frank , Håkansson Per
Published: July 2003

An electron injection system based on an indirectly heated ring‐shaped dispenser cathode has been developed and installed in a 7 Tesla Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. This new hardware design allows high‐rate electron capture dissociation (ECD) to be carried out by a hollow electron beam coaxial with the ion cyclotron resonance (ICR) trap. Infrared multiphoton dissociation (IRMPD) can also be performed with an on‐axis IR‐laser beam passing through a hole at the centre of the dispenser cathode. Electron and photon irradiation times of the order of 100 ms are required for efficient ECD and IRMPD, respectively. As ECD and IRMPD generate fragments of different types (mostly c, z and b, y, respectively), complementary structural information that improves the characterization of peptides and proteins by FTICR mass spectrometry can be obtained. The developed technique enables the consecutive or simultaneous use of the ECD and IRMPD methods within a single FTICR experimental sequence and on the same ensemble of trapped ions in multistage tandem (MS/MS/MS or MSn) mass spectrometry. Flexible changing between ECD and IRMPD should present advantages for the analysis of protein digests separated by liquid chromatography prior to FTICRMS. Furthermore, ion activation by either electron or laser irradiation prior to, as well as after, dissociation by IRMPD or ECD increases the efficiency of ion fragmentation, including the w‐type fragment ion formation, and improves sequencing of peptides with multiple disulfide bridges. The developed instrumental configuration is essential for combined ECD and IRMPD on FTICR mass spectrometers with limited access into the ICR trap. Copyright © 2003 John Wiley & Sons, Ltd.
Improved peptide sequencing using isotope information inherent in tandem mass spectra
Authors: Cannon William R. , Jarman Kenneth D.
Published: July 2003

We demonstrate here the use of natural isotopic ‘labels’ in peptides to aid in the identification of peptides with a de novo algorithm. Using data from ion trap tandem mass spectrometric (MS/MS) analysis of 102 tryptic peptides, we have analyzed multiple series of peaks within LCQ MS/MS spectra that ‘spell’ peptide sequences. Isotopic peaks from naturally abundant isotopes are particularly prominent even after peak centroiding on y‐ and b‐series ions and lead to increased confidence in the identification of the precursor peptides. Sequence analysis of the MS/MS data is accomplished by finding sequences and subsequences in a hierarchical manner within the spectra. Copyright © 2003 John Wiley & Sons, Ltd.
Electrospray mass spectrometry determination of poly(oxazolidine acetal)
Authors: Maślińska‐Solich J. , Kudrej‐Gibas E.
Published: July 2003

The polycondensation of terephthalaldehyde with 2‐amino‐2‐hydroxymethyl‐1,3‐propanediol (TRIS), or of terephthaldehyde with 2,2′‐(1,4‐phenylene)‐bis‐1,3‐(4,4‐dihydroxymethyl)oxazolidine (bis‐oxazolidine), using acidic catalysts, leads to the formation of linear polymers and macrocyclic compounds. The structure of the polymer was determined by 1H‐, 13C‐NMR spectroscopy and electrospray ionization mass spectrometry (ESI‐MS) analysis. ESI‐MS measurements were used to study the details of the polymer structure and support the alternating nature of equimolar amounts of oxazolidine and the cyclic acetal of terephthaldehyde in these macromolecules. Copyright © 2003 John Wiley & Sons, Ltd.
‘Bubble chamber model’ of fast atom bombardment induced processes
Authors: Kosevich Marina V. , Shelkovsky Vadim S. , Boryak Oleg A. , Orlov Vadim V.
Published: July 2003

A hypothesis concerning FAB mechanisms, referred to as a ‘bubble chamber FAB model’, is proposed. This model can provide an answer to the long‐standing question as to how fragile biomolecules and weakly bound clusters can survive under high‐energy particle impact on liquids. The basis of this model is a simple estimation of saturated vapour pressure over the surface of liquids, which shows that all liquids ever tested by fast atom bombardment (FAB) and liquid secondary ion mass spectrometry (SIMS) were in the superheated state under the experimental conditions applied. The result of the interaction of the energetic particles with superheated liquids is known to be qualitatively different from that with equilibrium liquids. It consists of initiation of local boiling, i.e., in formation of vapour bubbles along the track of the energetic particle. This phenomenon has been extensively studied in the framework of nuclear physics and provides the basis for construction of the well‐known bubble chamber detectors. The possibility of occurrence of similar processes under FAB of superheated liquids substantiates a conceptual model of emission of secondary ions suggested by Vestal in 1983, which assumes formation of bubbles beneath the liquid surface, followed by their bursting accompanied by release of microdroplets and clusters as a necessary intermediate step for the creation of molecular ions. The main distinctive feature of the bubble chamber FAB model, proposed here, is that the bubbles are formed not in the space and time‐restricted impact‐excited zone, but in the nearby liquid as a ‘normal’ boiling event, which implies that the temperature both within the bubble and in the droplets emerging on its burst is practically the same as that of the bulk liquid sample. This concept can resolve the paradox of survival of intact biomolecules under FAB, since the part of the sample participating in the liquid–gas transition via the bubble mechanism has an ambient temperature which is not destructive for biomolecules. Another important feature of the model is that the timescale of bubble growth is no longer limited by the relaxation time of the excited zone (∼10−12 s), but rather resembles the timescale characteristic of common boiling, sufficient for multiple interactions of gas molecules and formation of clusters. Further, when the bubbles burst, microdroplets are released, which implies that FAB processes are similar to those in spraying techniques. Thus, two processes contribute to the ion production, namely, release of volatile solvent clusters from bubbles and of non‐volatile solute from sputtered droplets. This view reconciles contradictory views on the dominance of either gas‐phase or liquid‐phase effects in FAB. Some other effects, such as suppression of all other ions by surface‐active compounds, are consistent with the suggested model. Copyright © 2003 John Wiley & Sons, Ltd.
Oxygen isotopes in nitrate: new reference materials for 18O:17O:16O measurements and observations on nitrate‐water equilibration
Authors: Böhlke J. K. , Mroczkowski S. J. , Coplen T. B.
Published: July 2003

Despite a rapidly growing literature on analytical methods and field applications of O isotope‐ratio measurements of NO3− in environmental studies, there is evidence that the reported data may not be comparable because reference materials with widely varying δ18O values have not been readily available. To address this problem, we prepared large quantities of two nitrate salts with contrasting O isotopic compositions for distribution as reference materials for O isotope‐ratio measurements: USGS34 (KNO3) with low δ18O and USGS35 (NaNO3) with high δ18O and ‘mass‐independent’ δ17O. The procedure used to produce USGS34 involved equilibration of HNO3 with 18O‐depleted meteoric water. Nitric acid equilibration is proposed as a simple method for producing laboratory NO3− reference materials with a range of δ18O values and normal (mass‐dependent) 18O:17O:16O variation. Preliminary data indicate that the equilibrium O isotope‐fractionation factor (α) between [NO3−] and H2O decreases with increasing temperature from 1.0215 at 22°C to 1.0131 at 100°C. USGS35 was purified from the nitrate ore deposits of the Atacama Desert in Chile and has a high 17O:18O ratio owing to its atmospheric origin. These new reference materials, combined with previously distributed NO3− isotopic reference materials IAEA‐N3 (=IAEA‐NO‐3) and USGS32, can be used to calibrate local laboratory reference materials for determining offset values, scale factors, and mass‐independent effects on N and O isotope‐ratio measurements in a wide variety of environmental NO3− samples. Preliminary analyses yield the following results (normalized with respect to VSMOW and SLAP, with reproducibilities of ±0.2–0.3‰, 1σ): IAEA‐N3 has δ18O = +25.6‰ and δ17O = +13.2‰; USGS32 has δ18O = +25.7‰; USGS34 has δ18O = −27.9‰ and δ17O = −14.8‰; and USGS35 has δ18O = +57.5‰ and δ17O = +51.5‰. Published in 2003 by John Wiley & Sons, Ltd.
Thermometer ions for matrix‐enhanced laser desorption/ionization internal energy calibration
Authors: Greisch J.‐F. , Gabelica V. , Remacle F. , De Pauw E.
Published: July 2003

This work describes a method to use relative fragmentation yields to characterize the internal energy distribution of ions produced by matrix‐enhanced laser desorption/ionization mass spectrometry (MELDI‐MS, see: Wright LG, Cooks RG, Wood KL. Biomed. Mass Spectrom. 1985; 12: 153–162). Assuming that the fragmentation proceeds statistically and that the collisions in the source lead to a Boltzmann‐like distribution of the internal energy, a characteristic parameter, the effective temperature, is introduced to describe the internal energy distribution of the ions observed. The hypotheses, advantages and drawbacks of the implementation of the method that uses substituted benzylpyridinium salts as thermometer ions are discussed. Use is made of two matrices that produce no matrix cations in MELDI and are suitable for small cationic salts. The actual value of this effective temperature significantly depends on an accurate determination of the threshold dissociation energies and on the time spent in the source, in addition to the statistical hypothesis itself. The method could be applied to normalize spectra in order to compare results issued from different instruments. Published in 2003 by John Wiley & Sons, Ltd.
High‐performance liquid chromatography/inductively coupled plasma mass spectrometry with iodine‐specific detection for profiling the metabolites produced in the earthworm Eisenia veneta by exposure to 2‐fluoro‐4‐iodoaniline
Authors: Duckett Catherine J. , Wilson Ian D. , Walker Heather , Abou‐Shakra Fadi , Lindon John C. , Nicholson Jeremy K.
Published: July 2003

High‐performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICPMS) provided a rapid and specific means for profiling the iodine‐containing metabolites produced by the earthworm Eisenia veneta following exposure to 2‐fluoro‐4‐iodoaniline. Profiles were obtained, using gradient reversed‐phase HPLC, from extracts of whole earthworms and from coleomic fluid with as little as 25 ng/peak of iodine detected. The use of ICPMS in this way provides a convenient means of determining the metabolic fate of iodinated compounds without the need for radiolabelled compounds. Copyright © 2003 John Wiley & Sons, Ltd.
A simple and rapid method for identifying the source of spilled oil using an electronic nose: confirmation by gas chromatography with mass spectrometry
Authors: Tzing Shin‐Hwa , Chang Jia‐Yaw , Ghule Anil , Chang Jia‐Jiu , Lo Bertrand , Ling Yong‐Chien
Published: July 2003

Two types of electronic nose (EN), different in operational principle, were used to identify the source of spilled oil in an accident. The suspected sources considered were petroleum oil reservoirs and pipelines located near the site of the accident. Gas chromatography/mass spectrometry (GC/MS), operated in both EI and CI modes, was employed to confirm the identified source. The advantage of multisensors in spatially resolved sensing for direct multicomponent analysis was explored to minimize tedious sample preparation procedures. Subsequent principal component analysis helped in identifying the source. The advantage of fast separation in temporally resolved sensing was explored to rapidly yield compositional information; the resulting graphical representations helped clarify the source. Traditional GC/MS not only confirms the identified spilled oil source, but also provides detailed diagnostic information such as total petroleum hydrocarbons, polycyclic aromatic hydrocarbons and their C1–C4 alkylated homologues, as well as the n‐alkanes, which are essential for follow‐up remedial and regulatory actions. The main use of the electronic nose was demonstrated to be as a simple and rapid screening method for identifying a spilled oil source. Copyright © 2003 John Wiley & Sons, Ltd.
Determination of coplanar and non‐coplanar polychlorinated biphenyls in human serum by gas chromatography with mass spectrometric detection: electron impact or electron‐capture negative ionization?
Authors: Turci Roberta , Bruno Franco , Minoia Claudio
Published: July 2003

A time‐ and cost‐saving method for the congener‐specific analysis of polychlorinated biphenyls (PCBs) in human serum has been developed and validated. After two fast extraction and clean‐up steps, analyses were performed using gas chromatography coupled with mass spectrometry with single ion monitoring (GC/SIM‐MS), either in electron impact (EI) or electron‐capture negative ionization (ECNI) mode. For the determination of dioxin‐like congeners, an improvement in EI‐MS sensitivity is desirable and use of NI is thus preferred. The procedure was validated for 12 dioxin‐like congeners by analyzing spiked samples on three different days and using 13C12‐labelled analogues as internal standards. When using an NCI source, the limit of quantification was assessed at 0.01 μg/L, except for PCBs #77 and #81, which cannot be reliably detected below 0.05 μg/L. For the lower chlorinated non‐dioxin‐like congeners, NI offers less selectivity because of limited fragmentation. Electron impact ionization and electron‐capture negative ionization mode can therefore be considered to be complementary for the determination of PCB congeners in the general population. Copyright © 2003 John Wiley & Sons, Ltd.
Analysis of the metal‐binding selectivity of the metallochaperone CopZ from Enterococcus hirae by electrospray ionization mass spectrometry
Authors: Urvoas Agathe , Amekraz Badia , Moulin Christophe , Le Clainche Loïc , Stöcklin Reto , Moutiez Mireille
Published: July 2003

Metallochaperones are soluble proteins involved in metal transport and regulation in vivo. Copper metallochaperones belong to a structural family of metal binding domains displaying a ferredoxin‐like fold (βαββαβ) and a consensus metal‐binding motif MXCXXC. The metal‐binding selectivities for this class of proteins are poorly documented so far. The present study focuses on the measurement of the selectivity of the copper metallochaperone CopZ from Enterococcus hirae for different metal ions using an experimental approach based on electrospray ionization mass spectrometry (ESI‐MS). All the metal cations tested, i.e. Cu(I), Cu(II), Hg(II), Cd(II) and Co(II), form specific metal complexes with CopZ. The study of a chemically modified CopZ as well as variants of CopZ in the active site demonstrated that the complexes observed by ESI‐MS, i.e. in the gas phase, corresponded to the complexes previously observed by other analytical methods in solution. Competition experiments allowed the classification of the metal ions by increasing affinities for CopZ as follows: Co ≪ Cd < Hg < Cu. A dissociation constant in the range of 20 μM was determined for cobalt. The affinity of CopZ for the other metals tested was found to be higher, with dissociation constants smaller than micromolar. Copyright © 2003 John Wiley & Sons, Ltd.
Sonic spray ionization applied to liquid chromatography/mass spectrometry analysis of endocrine‐disrupting chemicals in environmental water samples
Authors: Benijts Tom , Günther Wolfgang , Lambert Willy , Leenheer André De
Published: July 2003

A sonic spray ionization liquid chromatography/mass spectrometry (LC/SSI‐MS) procedure combined with off‐line solid‐phase extraction was optimized for the analysis of 20 endocrine‐disrupting chemicals (EDCs) in water samples. Method development included a comparison of the novel sonic spray ionization (SSI) with more traditional ion sources, i.e. pneumatically assisted electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). It was demonstrated that SSI and ESI spectra were very similar, but were more prone to the formation of solvent cluster ions as compared with APCI spectra. This phenomenon was most prominent for SSI and resulted in an increased chemical background in full‐scan mass spectra. However, this chemical noise did not affect the overall sensitivity of SSI and ESI. After optimization of LC and MS parameters, the LC/SSI‐MS method was validated. Recoveries ranged from 76.3 up to 113.4% for all compounds. Limits of detection (LOD) and quantitation (LOQ) were established between 3.0 and 11.5 ng/L and 9.9 and 38.0 ng/L, respectively. Within‐day (n = 5) and between‐day (n = 5) reproducibility were investigated at three levels and ranged from 3.3–16.5% and 7.6–19.2%, respectively. Eight‐point calibration curves were established and showed linearity for all compounds (r2 > 0.987) over a linear dynamic range of 10–10 000 ng/L. Copyright © 2003 John Wiley & Sons, Ltd.
Gas chromatography/isotope‐ratio mass spectrometry method for high‐precision position‐dependent15N and18O measurements of atmospheric nitrous oxide
Authors: Röckmann Thomas , Kaiser Jan , Brenninkmeijer Carl A. M. , Brand Willi A.
Published: July 2003

We describe an automated gas chromatography/isotope‐ratio mass spectrometry (GC/IRMS) method for the determination of the18O and position‐resolved15N content of nitrous oxide at natural isotope abundance. The position information is obtained from successive measurement of the isotopic composition of the N2O+ion atm/z44, 45, 46 and the NO+fragment ion atm/z30, 31. The fragment ion analysis is complicated by a non‐linearity in the mass spectrometer that has to be taken into account. Evaluation of the absolute peak areas allows for a simultaneous determination of the N2O mixing ratio for atmospheric samples. Samples with mixing ratios ranging from a few nmol/mol up to the percent level can be analyzed using different sample inlet systems. The high concentration inlet system provides an easy and quick method to carry out various diagnostic tests, in particular to perform realistic linearity tests. A gas chromatographic set‐up with a split column and a backflush possibility improves analytical precision and excludes interferences by substances with long retention times from preceding runs. We also describe a new open split interface that uses only a single transfer capillary to the mass spectrometer for sample and reference gas. Copyright © 2003 John Wiley & Sons, Ltd.
Development of a liquid chromatography/tandem mass spectrometry assay for the quantification of Aplidin®, a novel marine‐derived antineoplastic agent, in human plasma
Authors: Yin Jianming , Aviles Pablo , Lee William , Ly Carl , Floriano Pablo , Ignacio Manzanares , Faircloth Glynn
Published: July 2003

A rapid and sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) assay was developed and validated to quantify a novel marine‐derived depsipeptide, Aplidin®, in human plasma. The method was validated to demonstrate the specificity, recovery, limit of quantitation (LOQ), accuracy, and precision of measurements. The calibration range for Aplidin® was established using Aplidin® standards from 0.05–50 ng/mL in blank human plasma. The multiple reaction monitoring, based on the transition m/z 1110.7 → 295.3, was specific for Aplidin®, and that based on the transition m/z 1112.6 → 297.3 was specific for didemnin B (the internal standard); no endogenous materials interfered with the analysis of Aplidin® and didemnin B from blank human plasma. The assay was linear over the concentration range 0.05–50.0 ng/mL. The correlation coefficients for the calibration curves ranged from 0.9979 to 0.9999. The mean intra‐ and interday accuracies for all calibration standards (n = 12) ranged from 97 to 106% (≤6% bias), and the mean interday precision for all calibration standards was less than 8.3%. The mean intra‐ and interday assay accuracy for all quality control replicates (n = 12), determined at each QC level throughout the validated runs, remained below 12 and 7%, respectively. The mean intra‐ and interday assay precision was less than 13.1 and 10.7% for all QC levels, respectively. The assay is currently used to measure Aplidin® plasma concentrations to support clinical trials. Copyright © 2003 John Wiley & Sons, Ltd.
Analysis of oxidized epigallocatechin gallate by liquid chromatography/mass spectrometry
Authors: Mizooku Yasuo , Yoshikawa Muneyoshi , Tsuneyoshi Toshihiro , Arakawa Ryuichi
Published: July 2003

(−)‐Epigallocatechin gallate (EGCG) of catechins changes from non‐colored at around neutral pH to yellow at higher pH region in aqueous solution. The pH‐dependent oxidation of EGCG was analyzed by liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI‐MS/MS). LC/MS/MS analysis of EGCG and its related compounds, (−)‐epicatechin gallate (ECG) and (−)‐epigallocatechin (EGC), successfully elucidated the structure relationship of EGCG solution involving the color change reaction at different pH conditions. The oxidation species produced at alkaline pH was detected at a different retention time from EGCG in the chromatograms of the EGCG sample. The oxidation species was found to correspond to M+14 (where M is the molecular weight of EGCG), which has two hydrogen atoms removed and addition of one oxygen atom to the gallyl moiety in the B‐ring of EGCG. Copyright © 2003 John Wiley & Sons, Ltd.
Generation of experimental L x‐ray fluorescence cross‐sections for inter‐elements at inter‐energies EL1 ≤ E ≤ EK (computer program IGELCS)
Authors: Mittal Raj , Singh Meenu , Vandana
Published: July 2003

The experimental values of L x‐ray fluorescence (XRF) cross‐sections are not available for all the elements in the range La–U, at all the photon energies E in the range EL1 ≤ E ≤ EK. To generate L XRF cross‐sections, where experimental measurements are not available, two empirical relations have been developed, one between the L XRF cross‐sections and photon energy and the other between the L XRF cross‐sections and atomic number. For the measured data on L XRF cross‐sections at incident energies between Ll and K edges of an element and the data on L XRF cross‐sections for elements in the range 57 ≤ Z ≤ 92 at an energy value, polynomial fits have been derived. The L XRF cross‐section values generated with the derived empirical relations were found to be in agreement with the experimental values within their experimental uncertainties. Subsequently, a software code IGELCS was developed to interpolate and to generate the cross‐sections at inter‐energies and for inter‐elements in a single computer run. The running of the software requires minimum input data on five elements at five common energies. Copyright © 2003 John Wiley & Sons, Ltd.
Compton scattering of 59.54 keV γ‐rays from Fe and p‐Si samples in an external magnetic field
Authors: Şahin Yusuf , Demir Demet
Published: July 2003

We report on the Compton scattering of photons from samples whose surface charge density distributions are changed by an external magnetic field. We performed a Compton scattering experiment known to be particularly sensitive to the behavior of the relatively slower moving outer electrons (valence electrons) involved in bonding in condensed matter. The external magnetic field was used to change the surface charge density distributions of Fe and p‐Si samples. Samples were located in the external magnetic field of intensity 215 G and in a direction which was perpendicular both to the current and surface of the samples bombarded by 59.5 keV γ‐photons emitted from an Am‐241 point source. Currents in the ranges 0–8.5 A and 0–300 µA were applied to the Fe and p‐Si samples, respectively. The Compton scattered photons at an angle of 100° were detected by an Si(Li) detector. It was observed that the counts acquired under the Compton peaks tended to decrease linearly with increasing current in a magnetic field. The results show that positive charge carriers behave like negative charge carriers and electrons are more effective than holes in the Compton scattering of γ‐rays. Copyright © 2003 John Wiley & Sons, Ltd.
Evaluation of the uncertainty of element determination using the energy‐dispersive x‐ray fluorescence technique and the emission–transmission method
Authors: Wegrzynek D. , Markowicz A. , Chinea‐Cano E. , Bamford S.
Published: July 2003

A detailed study of the uncertainty quantification procedure for the determination of element mass fractions in a soil matrix by using energy‐dispersive x‐ray fluorescence spectrometry and the emission–transmission method was carried out. The particular case of secondary target excitation with an Mo target and Mo anode x‐ray tube was addressed. The effects of simplification of the theoretical model on the determined mass fractions of elements were studied. The main contributions to the uncertainty were identified and the ways of reducing their magnitude were indicated. The approach was found to be helpful in designing an optimum analytical strategy. It can also be used as guidance for assessing the uncertainty in other modes of x‐ray fluorescence analysis. Copyright © 2003 John Wiley & Sons, Ltd.
Selective excitation and integral counting of x‐ray fluorescence (SEICXRF)
Authors: Figueroa R.
Published: July 2003

This paper proposes a spectrometric method for x‐ray fluorescence, based on selective excitation and integral counting of the emitted photons by the sample. It is named SEICXRF (Selective Excitation and Integral Counting of X‐Ray Fluorescence). The general characteristics of the method are shown: the spectrometer, the spectrum acquisition, the effects involved in the determination of the jump intensity and their respective algorithms (the primary and secondary intensities and other unexpected effects), its capacity to identify elements, its sensitivity, its limitations and scope. Copyright © 2003 John Wiley & Sons, Ltd.
Algorithm of fundamental parameters for the SEICXRF method
Authors: García M. , Figueroa R. , Rivera R.
Published: July 2003

An algorithm based on fundamental parameters and applied to the SEICXRF method, developed by one of the authors, is presented. The methodology used in the calculation is similar to the Rousseau fundamental parameters method, but the main difference is the considerations about the x‐ray secondary fluorescence. In the new experimental method, the fluorescence yield by photons corresponding to the absorption edges with energies greater than the absorption edge energy of analyte does not occur. This secondary fluorescence appears in the calculation of the total fluorescence as a consequence of the integral count of the fluorescent emission from the sample. It is created by the primary fluorescence yield of the atoms whose absorption edge energies are less than the primary fluorescence energy of the analyte. The algorithm also considers the effect of the decrease of the sample fluorescent background just at the jump, originated by the change of the absorption coefficient at the absorption edge energy of the element of interest. Considering these two effects, including the primary fluorescence in the calculation, allows one to obtain the net fluorescence originated by the analyte at its own absorption edge. Copyright © 2003 John Wiley & Sons, Ltd.
Comparison between intensity jumps in experimental, simulated and theoretical multielemental spectra
Authors: Figueroa R. , García M. , Brusa D.
Published: July 2003

The results obtained by applying the theory developed for the SEICXRF method and applying a Monte Carlo simulation code (MCS) are compared with the experimental data in order to validate this theory. Specifically, an assay is made with the spectra corresponding to a brass sample and a soil sample. The experimental data were corrected considering the chamber efficiency and the dead time of the detection system. The considerations taken into account in order to obtain a correct comparison between theory and experiment are discussed in detail. Good agreement between spectra is observed, taking as reference the given values of the elemental composition. The experimental intensity jumps are in agreement with those predicted by the theory and by the MCS. Copyright © 2003 John Wiley & Sons, Ltd.
An investigation of x‐ray escape for an HPGe detector
Authors: Can Cüneyt , Bilgici Serdar Ziya
Published: July 2003

X‐ray escape peaks for a planar HPGe detector were investigated for a point source of photons with 59.5 keV energy. The effect of the solid angle for the incident photons on the escape probability of Ge K x‐rays was studied using collimators with varying apertures. A Monte Carlo program was also developed to estimate the probability of escape for various mechanisms and routes. The experimental and simulation results showed that the escape probability is essentially constant for a wide range of collimator radii, but at first starts to increase and then becomes constant when the side surface of the detector becomes accessible for escape with larger collimators. Copyright © 2003 John Wiley & Sons, Ltd.
Escape of photoelectrons and Compton‐scattered photons from an HPGe detector
Authors: Can Cüneyt
Published: July 2003

The response function of a planar HPGe detector due to escape of photoelectrons and Compton‐scattered photons was studied for a point source with 59.5 keV energy. It was shown that both mechanisms, in addition to Ge x‐ray escape, leading to partial deposition of energy, could be observed in the same experiment. A Monte Carlo program was used to investigate these components of the response function. The results indicate that although the escape of scattered photons and Ge x‐rays are of the same magnitude, the escape of photoelectrons plays a more important role in the efficiency of a detector. Copyright © 2003 John Wiley & Sons, Ltd.
UNIQUENESS IN THE CAUCHY PROBLEM FOR PARABOLIC EQUATIONS
Authors: Ferretti Elisa
Published: July 2003

We discuss the problem of the uniqueness of the solution to the Cauchy problem for second-order, linear, uniformly parabolic differential equations. For most uniqueness theorems the solution must be uniformly bounded with respect to the time variable $t$, but some authors have shown an interest in relaxing the growth conditions in time.

In 1997, Chung proved that, in the case of the heat equation, uniqueness holds under the restriction: $|u(x,t)|\leq C\exp[(a/t)^{\alpha}+a|x|^2]$, for some constants $C,a>0$, $0\lt\alpha\lt1$. The proof of Chung’s theorem is based on ultradistribution theory, in particular it relies heavily on the fact that the coefficients are constants and that the solution is smooth. Therefore, his method does not work for parabolic operators with arbitrary coefficients. In this paper we prove a uniqueness theorem for uniformly parabolic equations imposing the same growth condition as Chung on the solution $u(x,t)$. At the centre of the proof are the maximum principle, Gaussian-type estimates for short cylinders and a boot-strapping argument.

AMS 2000 Mathematics subject classification: Primary 35K15
EPIMORPHISMS ONTO DERIVATION ALGEBRAS
Authors: Villena A. R.
Published: July 2003

We prove that the separating space of an epimorphism from a Lie–Banach algebra onto the (continuous) derivation algebra $\mathfrak{Der}(A)$ of a Banach algebra $A$ consists of derivations which map into the radical of $A$.

AMS 2000 Mathematics subject classification: Primary 46H40; 46H70. Secondary 47B47; 47B48
THE HILLE–YOSIDA THEOREM FOR LOCAL CONVOLUTED SEMIGROUPS
Authors: Keyantuo Valentin , Müller Claus , Vieten Peter
Published: July 2003

The characterization theorem for the Banach-space-valued local Laplace transform established by Keyantuo, Müller and Vieten is used to obtain a real variable characterization of generators of local convoluted semigroups. The concept of local convoluted semigroups extends that of distribution as well as ultradistribution semigroups. Complete characterizations existed only for exponentially bounded semigroups integrated $\alpha$ times, whereas for the non-exponential case generation results had been obtained in terms of complex conditions only.

AMS 2000 Mathematics subject classification: Primary 47D03; 47D06; 44A10
OPTIMAL EMBEDDINGS OF DISTRIBUTIONS INTO ALGEBRAS
Authors: Vernaeve H.
Published: July 2003

Let $\varOmega$ be a convex, open subset of $\mathbb{R}^n$ and let $\mathcal{D}'(\varOmega)$ be the space of distributions on $\varOmega$. It is shown that there exist linear embeddings of $\mathcal{D}'(\varOmega)$ into a differential algebra that commute with partial derivatives and that embed $\mathcal{C}^{\infty}(\varOmega)$ as a subalgebra. This embedding appears to be the first one after Colombeau’s to possess these properties. We show that many nonlinear operations on distributions can be defined that are not definable in the Colombeau setting.

AMS 2000 Mathematics subject classification: Primary 46F30. Secondary 13C11
STABILITY OF THE DEFICIENCY INDICES OF SYMMETRIC OPERATORS UNDER SELF-ADJOINT PERTURBATIONS
Authors: Kissin Edward
Published: July 2003

Let $S$ and $T$ be symmetric unbounded operators. Denote by $\overline{S+T}$ the closure of the symmetric operator $S+T$. In general, the deficiency indices of $\overline{S+T}$ are not determined by the deficiency indices of $S$ and $T$. The paper studies some sufficient conditions for the stability of the deficiency indices of a symmetric operator $S$ under self-adjoint perturbations $T$. One can associate with $S$ the largest closed $^*$-derivation $\delta_{S}$ implemented by $S$. We prove that if the unitary operators $\exp(\ri tT)$, for $t\in\mathbb{R}$, belong to the domain of $\delta_{S}$ and $\delta_{S}(\exp(\ri tT))\rightarrow0$ in the strong operator topology as $t\rightarrow0$, then the deficiency indices of $S$ and $\overline{S+T}$ coincide. In particular, this holds if $S$ and $\exp(\ri tT)$ commute or satisfy the infinitesimal Weyl relation.

We also study the case when $S$ and $T$ anticommute: $\exp(-\ri tT)S\subseteq S\exp(\ri tT)$, for $t\in\mathbb{R}$. We show that if the deficiency indices of $S$ are equal, or if the group $\{\exp(\ri tT):t\in\mathbb{R}\}$ of unitary operators has no stationary points in the deficiency space of $S$, then $S$ has a self-adjoint extension which anticommutes with $T$, the operator $S+T$ is closed and the deficiency indices of $S$ and $S+T$ coincide.

AMS 2000 Mathematics subject classification: Primary 47B25
BOUNDARY-CHAOTIC BEHAVIOUR OF CONTINUOUS FUNCTIONS UNDER THE ACTION OF OPERATORS
Authors: Bernal-González Luis , Calderón-Moreno María del Carmen
Published: July 2003

In this paper we introduce two classes of operators on spaces of continuous functions with values in $F$-spaces under the action of which many functions behave chaotically near the boundary. Several examples—including onto linear operators, left and right composition operators, multiplication operators, and operators with pointwise dense range or with some stability property—are given. This new theory extends one recently developed on spaces of holomorphic functions.

AMS 2000 Mathematics subject classification: Primary 47B38. Secondary 30D40; 46E10; 54D45
QUANTUM CHANNELS, WAVELETS, DILATIONS AND REPRESENTATIONS OF $\mathcal{O}_{n}$
Authors: Kribs David W.
Published: July 2003

We show that the representations of the Cuntz $C^*$-algebras $\mathcal{O}_n$ which arise in wavelet analysis and dilation theory can be classified through a simple analysis of completely positive maps on finite-dimensional space. Based on this analysis, we find an application in quantum information theory; namely, a structure theorem for the fixed-point set of a unital quantum channel. We also include some open problems motivated by this work.

AMS 2000 Mathematics subject classification: Primary 46L45; 47A20; 46L60; 42C40; 81P15
INDECOMPOSABLE NON-HOLONOMIC $\mathcal{D}$-MODULES IN DIMENSION $2$
Authors: Coutinho S. C.
Published: July 2003

A module of a ring of differential operators $\mathcal{D}$ over a smooth surface has order $1$ if it is isomorphic to a factor module of $\mathcal{D}$ by a cyclic ideal generated by an operator of order $1$. Let $k$ be a positive integer. We give conditions under which an indecomposable $\mathcal{D}$-module of order $1$ is GK-critical of length $k$. We also give examples of indecomposable, non-critical, $\mathcal{D}$-modules whose subfactors have order $1$.

AMS 2000 Mathematics subject classification: Primary 16S32. Secondary 37F75
FINITE AND LOCAL LAPLACE TRANSFORMS IN BANACH SPACES
Authors: Keyantuo Valentin , Müller Claus , Vieten Peter
Published: July 2003

We establish two characterizations of local Laplace transforms in Banach spaces. The first result follows the classic approach of Widder, while the second is in terms of vector-valued moment sequences. As a consequence, we derive characterizations of nilpotent semigroups.

AMS 2000 Mathematics subject classification: Primary 44A10; 47D03
HILBERT MODULAR PSEUDODIFFERENTIAL OPERATORS OF MIXED WEIGHT
Authors: Lee Min Ho , Myung Hyo Chul
Published: July 2003

We introduce an action of a discrete subgroup $\varGamma$ of $SL(2,\mathbb{R})^n$ on the space of pseudodifferential operators of $n$ variables, and construct a map from the space of Hilbert modular forms for $\varGamma$ to the space of pseudodifferential operators invariant under such a $\varGamma$-action, which is a lifting of the symbol map of pseudodifferential operators. We also obtain a necessary and sufficient condition for a certain type of pseudodifferential operator to be $\varGamma$-invariant.

AMS 2000 Mathematics subject classification: Primary 11F41; 35S05
ON FACTORIZATION IN BLOCK MONOIDS FORMED BY $\{\bar{1},\bar{a}\}$ IN $\mathbb{Z}_{n}$
Authors: Chapman Scott T. , Smith William W.
Published: July 2003

We consider the factorization properties of block monoids on $\mathbb{Z}_n$ determined by subsets of the form $S_a=\{\bar{1},\bar{a}\}$. We denote such a block monoid by $\mathcal{B}_a(n)$. In §2, we provide a method based on the division algorithm for determining the irreducible elements of $\mathcal{B}_a(n)$. Section 3 offers a method to determine the elasticity of $\mathcal{B}_a(n)$ based solely on the cross number. Section 4 applies the results of §3 to investigate the complete set of elasticities of Krull monoids with divisor class group $\mathbb{Z}_n$.

AMS 2000 Mathematics subject classification: Primary 20M14; 20D60; 13F05