Showing papers on "Electrospray ionization published in 2001"

An introduction to quadrupole-time-of-flight mass spectrometry.

Abstract: A brief introduction is presented to the basic principles and application of a quadrupole–time-of-flight (TOF) tandem mass spectrometer. The main features of reflecting TOF instruments with orthogonal injection of ions are discussed. Their operation and performance are compared with those of triple quadrupoles with electrospray ionization and matrix-assisted laser desorption/ionization (MALDI) TOF mass spectrometers. Examples and recommendations are provided for all major operational modes: mass spectrometry (MS) and tandem MS (MS/MS), precursor ion scans and studies of non-covalent complexes. Basic algorithms for liquid chromatography/MS/MS automation are discussed and illustrated by two applications. Copyright  2001 John Wiley & Sons, Ltd.

Resolution and identification of elemental compositions for more than 3000 crude acids in heavy petroleum by negative-ion microelectrospray high-field Fourier transform ion cyclotron resonance mass spectrometry

Abstract: Although crude acids are minor constituents in petroleum, they have significant implications for crude oil geochemistry, corrosion, and commerce. We have previously demonstrated that a single positive-ion electrospray ionization (ESI) high-field Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) experiment can resolve and identify 3000 chemically different elemental compositions of bases (basic nitrogen compounds) in a crude oil. Here, we show that negative-ion ESI high-field FT-ICR MS can selectively ionize and identify naphthenic acids without interference from the hydrocarbon background. When combined with prechromatographic separation, ESI FT-ICR MS reveals an even more detailed acid composition. An average mass resolving power, m/Δm50% ≥ 80 000 (Δm50% is mass spectral peak full width at half-maximum peak height) across a wide mass range (200 < m/z < 1000), distinguishes as many as 15 distinct chemical formulas within a 0.26 Da mass window. Collectively, more than 3000 chemically ...

Integrated Microfluidic System Enabling Protein Digestion, Peptide Separation, and Protein Identification

Abstract: An integrated platform is presented for rapid and sensitive protein identification by on-line protein digestion and analysis of digested proteins using electrospray ionization mass spectrometry or transient capillary isotachophoresis/capillary zone electrophoresis with mass spectrometry detection. A miniaturized membrane reactor is constructed by fabricating the microfluidic channels on a poly(dimethylsiloxane) substrate and coupling the microfluidics to a poly(vinylidene fluoride) porous membrane with the adsorbed trypsin. On the basis of he large surface area-to-volume ratio of porous membrane media, adsorbed trypsin onto the poly(vinylidene fluoride) membrane is employed for achieving ultrahigh catalytic turnover. The extent of protein digestion in a miniaturized membrane reactor can be directly controlled by the residence time of protein analytes inside the trypsin-adsorbed membrane, the reaction temperature, and the protein concentration. The resulting peptide mixtures can either be directly analyzed...

Detection of Multiple Protein Conformational Ensembles in Solution via Deconvolution of Charge-State Distributions in ESI MS

Abstract: Monitoring the changes in charge-state distributions of protein ions in electrospray ionization (ESI) mass spectra has become one of the commonly accepted tools to detect large-scale conformational changes of proteins in solution. However, these experiments produce only qualitative, low-resolution information. Our goal is to develop a procedure that would produce quantitative data on protein conformational isomers coexisting in solution at equilibrium. To that end, we have examined the evolution of positive ion charge-state distributions in the

Charge-reduced nano electrospray ionization combined with differential mobility analysis of peptides, proteins, glycoproteins, noncovalent protein complexes and viruses.

Abstract: This study explores the potential of a novel electrospray-based method, termed gas-phase electrophoretic mobility molecular analysis (GEMMA), allowing the molecular mass determination of peptides, proteins and noncovalent biocomplexes up to 2 MDa (dimer of immunglobulin M). The macromolecular ions were formed by nano electrospray ionization (ESI) in the ‘cone jet’ mode. The multiple charged state of the monodisperse droplets/ions generated was reduced by means of bipolar ionized air (generated by an α-particle source) to yield exclusively singly charged positive and negative ions as well as neutrals. These ions are separated subsequently at atmospheric pressure using a nano differential mobility analyzer according to their electrophoretic mobility in air. Finally, the ions are detected using a standard condensation particle counter. Data were expressed as electrophoretic mobility diameters by applying the Millikan equation. The measured electrophoretic mobility diameters, or Millikan diameters, of 32 well-defined proteins were plotted against their molecular weights in the range 3.5 to 1920 kDa and exhibited an excellent squared correlation coefficient (r2 = 0.999). This finding allowed the exact molecular weight determination of large (glyco)proteins and noncovalent biocomplexes by means of this new technique with a mass accuracy of ±5.6% up to 2 MDa at the femtomole level. From the molecular masses of the weakly bound, large protein complexes thus obtained, the binding stoichiometry of the intact complex and the complex stability as a function of pH, for example, can be derived. Examples of specific protein complexes, such as the avidin or catalase homo-tetramer, are used to illustrate the potential of the technique for characterization of high-mass biospecific complexes. A discussion of current and future applications of charge-reduced nano ESI GEMMA, such as chemical reaction monitoring (reduction process of immunglobulin G) or size determination of an intact virus, a supramolecular complex, and monitoring of partial dissociation of a human rhinoviruses, is provided. Copyright © 2001 John Wiley & Sons, Ltd.

Electrospray ionization mass spectrometry of oligonucleotide complexes with drugs, metals, and proteins

Abstract: I. Introduction 61 II. Binding of Small Molecules to DNA 62 A. Covalent Binding 62 B. Reversible (Noncovalent) DNA-Binding Agents 65 III. DNA-Metal Ion Complexes 67 A. Platinum Complexes 70 B. Other Metal Ions 73 IV. DNA-Protein Complexes 74 A. Introduction 74 B. ESI-MS of DNA-Protein Complexes 76 C. ESI-MS Analysis of Proteolytic Products of DNA-Protein Complexes 79 D. ESI-MS of Ternary DNA-Protein-Ligand Complexes 80 V. Conclusions 80 Abbreviations 81 References 81 --Interactions of DNA with drugs, metal ions, and proteins are important in a wide variety of biological processes. With the advent of electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI), mass spectrometry (MS) is now a well-established tool for the characterization of the primary structures of biopolymers. The gentle nature of the ESI process, however, means that ESI-MS is also finding application for the study of noncovalent and other fragile biomolecular complexes. We outline here the progress, to date, in the use of ESI-MS for the study of noncovalent drug-DNA and protein-DNA complexes together with strategies that can be employed to examine the binding of small molecules and metal complexes to DNA. In the case of covalent complexes with DNA, sequence information can be derived from ESI-MS used in conjunction with tandem mass spectrometry (MS/MS) and/or enzymatic digestion. MS/MS can also be used to probe the relative binding affinities of drugs that bind to DNA via noncovalent interactions. Overall, the work in this area, to date has demonstrated that ESI-MS and MS/MS will prove to be valuable complements to other structural methods, offering advantages in terms of speed, specificity, and sensitivity. (c) 2001 John Wiley & Sons, Inc.

Structure characterization of flavonoid O-diglycosides by positive and negative nano-electrospray ionization ion trap mass spectrometry

Abstract: Isomeric flavonoid O-diglycosides were analyzed by positive and negative nano-electrospray ionization (ESI) ion trap mass spectrometry (ITMS} in order to evaluate whether the two most common interglycosidic linkage Types, i.e. 1 --> 2 and 1 --> 6, found for glycosides containing a rhamnosylglucose glycan part can be differentiated. In the positive ion mode the degree of internal glucose residue loss was found to be strongly dependent on the aglycone type and was very pronounced for aglycones of the flavanone type. The relative abundance of the Y-type ions formed by fragmentation at glycosidic bonds only allows one to infer the interglycosidic linkage types in the case of flavone O-diglycosides. In contrast, the negative ion mode makes a clear differentiation between a rutinoside (1 --> 6) and a neohesperidoside (1 --> 2) glycan residue possible for all aglycone types. The neohesperidose-containing compounds could be characterized by additional product ions. When the compounds were dissolved in pure methanol a molecular radical ion tvas found to be the base peak in nano-ESI. Copyright (C) 2001 John Wiley & Sons, Ltd.

The effect of the source pressure on the abundance of ions of noncovalent protein assemblies in an electrospray ionization orthogonal time-of-flight instrument.

Abstract: The effect of elevating the pressure in the interface region of an electrospray ionization orthogonal time-of-flight mass spectrometer on the ion intensity of different noncovalent protein assemblies has been investigated. Elevating the pressure in the interface region generally led to an enhanced detection of high m/z ions. The optimum pressure was found to be dependent on the m/z value of the ions. This pressure effect should be carefully addressed when relating ion abundance in the mass spectra to solution phase abundance of noncovalent protein assemblies.

Supercharged protein and peptide ions formed by electrospray ionization.

Abstract: The multiple charging of large molecules in electrospray ionization provides key advantages for obtaining accurate molecular weights by mass spectrometry and for obtaining structural information by tandem mass spectrometry and MS(n) experiments. Addition of glycerol or m-nitrobenzyl alcohol into the electrospray solutions dramatically increases both the maximum observed charge state and the abundances of the high charge states of protein and peptide ions. Adding glycerol to acidified aqueous solutions of cytochrome c shifts the most abundant charge state from 17+ to 21+, shifts the maximum charge state from 20+ to 23+, and shifts the average charge state from 16.6+ to 20.9+. Much less m-nitrobenzyl alcohol (<1%) is required to produce similar results. With just 0.7% m-nitrobenzyl alcohol, even the 24+ charge state of cytochrome c is readily observed. Similar results are obtained with myoglobin and (Lys)4. For the latter molecule, the 5+ charge state is observed in the electrospray mass spectrum obtained from solutions containing 6.7% m-nitrobenzyl alcohol. This charge state corresponds to protonation of all basic sites in this peptide. Although the mechanism for enhanced charging is unclear, it does not appear to be a consequence of conformational changes of the analyte molecules. This method of producing highly charged protein ions should be useful for improving the performance of mass measurements on mass spectrometers with performances that decrease with increasing m/z. This should also be particularly useful for tandem mass spectrometry experiments, such as electron capture dissociation, for which highly charged ions are desired.

High-performance liquid chromatography-electrospray ionization mass spectrometry using monolithic capillary columns for proteomic studies.

Abstract: The use of tetrahydrofuran/decanol as porogens for the fabrication of micropellicular poly(styrene/divinylbenzene) monoliths enabled the rapid and highly efficient separation of peptides and proteins by reversed-phase high-performance liquid chromatography (RP-HPLC). In contrast to conventional, granular, porous stationary phases, in which the loading capacity is a function of molecular mass, the loadability of the monoliths both for small peptides and large proteins was within the 0.40.9-pmol range for a 60- x 0.2-mm capillary column. Lower limits of detection obtained by measuring UV-absorbance at 214 nm with a 3-nl capillary detection cell were 500 amol for an octapeptide and 200 amol for ribonuclease A. Upon reduction of the concentration of trifluoroacetic acid in the eluent from the commonly used 0.1-0.2 to 0.05%, the separation system was successfully coupled to electrospray ionization mass spectrometry (ESI-MS) at the cost of only a small decrease in separation efficiency. Detection limits for proteins with ESI-MS were in the lower femtomole range. High-quality mass spectra were extracted from the reconstructed ion chromatograms, from which the masses of both peptides and proteins were deduced at a mass accuracy of 50-150 ppm. The applicability of monolithic column technology in proteomics was demonstrated by the mass fingerprinting of tryptic peptides of bovine catalase and human transferrin and by the analysis of membrane proteins related to the photosystem II antenna complex of higher plants.

Choosing between atmospheric pressure chemical ionization and electrospray ionization interfaces for the HPLC/MS analysis of pesticides.

Abstract: An evaluation of over 75 pesticides by high-performance liquid chromatography/mass spectrometry (HPLC/MS) clearly shows that different classes of pesticides are more sensitive using either atmospheric pressure chemical ionization (APCI) or electrospray ionization (ESI) For example, neutral and basic pesticides (phenylureas, triazines) are more sensitive using APCI (especially positive ion) While cationic and anionic herbicides (bipyridylium ions, sulfonic acids) are more sensitive using ESI (especially negative ion) These data are expressed graphically in a figure called an ionization-continuum diagram, which shows that protonation in the gas phase (proton affinity) and polarity in solution, expressed as proton addition or subtraction (pKa), is useful in selecting APCI or ESI Furthermore, sodium adduct formation commonly occurs using positive ion ESI but not using positive ion APCI, which reflects the different mechanisms of ionization and strengthens the usefulness of the ionization-continuum diagram

Molecular Resolution and Fragmentation of Fulvic Acid by Electrospray Ionization/Multistage Tandem Mass Spectrometry

Abstract: Molecular weight distributions of fulvic acid from the Suwannee River, Georgia, were investigated by electrospray ionization/quadrupole mass spectrometry (ESI/ QMS), and fragmentation pathways of specific fulvic acid masses were investigated by electrospray ionization/ion trap multistage tandem mass spectrometry (ESI/MST/ MS). ESI/QMS studies of the free acid form of low molecular weight poly(carboxylic acid) standards in 75% methanol/25% water mobile phase found that negative ion detection gave the optimum generation of parent ions that can be used for molecular weight determinations. However, experiments with poly(acrylic acid) mixtures and specific high molecular weight standards found multiply charged negative ions that gave a low bias to molecular mass distributions. The number of negative charges on a molecule is dependent on the distance between charges. ESI/MST/MS of model compounds found characteristic water loss from alcohol dehydration and anhydride formation, as well as CO 2 loss from decarboxylation, and CO loss from ester structures. Application of these fragmentation pathways to specific masses of fulvic acid isolated and fragmented by ESI/MST/MS is indicative of specific structures that can serve as a basis for future structural confirmation after these hypothesized structures are synthesized.

Mass Spectrometry of an Intact Virus

Abstract: these limitations for the analysis of whole viruses. Charge-detection mass spectrometry is a relatively new technique that circumvents limitations associated with detecting large, highly charged ions by making a simultaneous measurement of charge (z) and mass-to-charge (m/z) ratio for individual ions. The detection technique permits the mass analysis of electrospray ions with virtually unlimited mass [10‐14] and has been performed on both Fourier-transform ioncyclotron resonance [14] and time-of-flight [11‐13] mass analyzers. The electrospray ionization source used in these studies [11] produced an aerosol of highly-charged virus particles in the ion-evaporation region of the electrospray ion source at atmospheric pressure. Virus ions pass one at a time through a small metal flight tube attached to a charge-sensitive preamplifier that captures their image current, the magnitude of which is proportional to the ions charge. In addition, by measuring the time-of-flight [15] of each ion through the flight tube the m/z value can be determined. The mass of each ion is obtained from a combination of both the charge and m/z value, where the ion charge can typically be determined with a precision of better than 75 z (as demonstrated in previous experiments with microparticles). A more complete description of the experiments and the system is published else

Desorption/ionization on silicon (DIOS): A diverse mass spectrometry platform for protein characterization

Abstract: Since the advent of matrix-assisted laser desorption/ionization and electrospray ionization, mass spectrometry has played an increasingly important role in protein functional characterization, identification, and structural analysis. Expanding this role, desorption/ionization on silicon (DIOS) is a new approach that allows for the analysis of proteins and related small molecules. Despite the absence of matrix, DIOS-MS yields little or no fragmentation and is relatively tolerant of moderate amounts of contaminants commonly found in biological samples. Here, functional assays were performed on an esterase, a glycosidase, a lipase, as well as exo- and endoproteases by using enzyme-specific substrates. Enzyme activity also was monitored in the presence of inhibitors, successfully demonstrating the ability of DIOS to be used as an inhibitor screen. Because DIOS is a matrix-free desorption technique, it also can be used as a platform for multiple analyses to be performed on the same protein. This unique advantage was demonstrated with acetylcholine esterase for qualitative and quantitative characterization and also by its subsequent identification directly from the DIOS platform.

Packed Capillary Reversed-Phase Liquid Chromatography with High-Performance Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry for Proteomics

Abstract: In this study, high-efficiency packed capillary reversed-phase liquid chromatography (RPLC) coupled on-line with high-performance Fourier transform ion cyclotron resonance (FTICR) mass spectrometry has been investigated for the characterization of complex cellular proteolytic digests. Long capillary columns (80-cm) packed with small (3-μm) C18 bonded particles provided a total peak capacity of ∼1000 for cellular proteolytic polypeptides when interfaced with an ESI-FTICR mass spectrometer under composition gradient conditions at a pressure of 10 000 psi. Large quantities of cellular proteolytic digests (e.g., 500 μg) could be loaded onto packed capillaries of 150-μm inner diameter without a significant loss of separation efficiency. Precolumns with suitable inner diameters were found useful for improving the elution reproducibility without a significant loss of separation quality. Porous particle packed capillaries were found to provide better results than those containing nonporous particles because of th...

Elemental Composition Analysis of Processed and Unprocessed Diesel Fuel by Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Abstract: High-resolution (100 000 < m/Δm50% < 250 000, in which Δm50% denotes mass spectral peak full width at half-maximum height) electrospray ionization Fourier transform ion cyclotron resonance positive-ion mass spectra of unprocessed (and processed) diesel fuels resolves approximately 500 (and 200) chemically different constituents over a mass range from 200 to 452 Da, with as many as 6 resolved elemental compositions at a given nominal mass. Molecular formulas were assigned from accurate mass measurement to within ±1 ppm. Compound types were identified by Kendrick mass analysis. On the basis of the experimental behavior of model compounds, electrospray ionization was found to ionize selectively basic pyridine homologuescompounds responsible for deactivation of hydrotreatment catalysts and instability of fuels during storage. Compound classes identified in the unprocessed diesel fuel include those containing N, N2, NS, NO, N2O, O2, and SO and, in the processed diesel, N, N2, NO2, and SO. Comparison of unproce...

Collision-induced fragmentation of deprotonated methoxylated flavonoids, obtained by electrospray ionization mass spectrometry.

Abstract: Electrospray operated in the negative mode was used to analyse methoxylated flavonoids. They were found to produce radical anions by collision-induced fragmentation of the aglycones. Loss of a methyl group from the deprotonated molecule corresponding to [M − H − 15]−. ions, as well as [M − H − 15–28]−. and [M − H − 15–29]− fragment ions, were found to constitute the characteristic fragmentation for the monomethoxylated species, whereas [M − H − 15]−., [M − H − 30]− and [M − H − 30–28]− were predominant for the polymethoxylated species. Obtained under similar conditions, the product-ion spectra of isomeric compounds were characteristically different. It is therefore possible to distinguish between methoxylated flavonoids with identical molecular mass, e.g. when screening plant extracts for flavonoid composition. However, comparison with standard compounds is necessary for the identification of unknown flavonoid aglycones. Copyright © 2001 John Wiley & Sons, Ltd.

Reduction of signal suppression effects in ESI-MS using a nanosplitting device.

Abstract: Electrospray ionization mass spectrometry is a valuable tool in the identification and quantification of drug metabolites in biological fluids. However, there are many instances where matrix components present in these fluids interfere with analyte detection and prevent the acquisition of accurate or complete results. In some instances, the matrix can suppress ionization to such an extent that analytes are completely undetectable by MS. In this work, we investigate how ionization and ion-transfer efficiencies are affected by drastically reducing the flow into the MS. A postcolumn concentric flow-splitting device was constructed to allow the measurement of analyte signal and ionization suppression across a range of flow rates (0.1−200 μL/min). Using this device, the effects of flow rate on signal intensity and ionization suppression were measured in analytical experiments that included flow injection analysis MS, postcolumn addition LC−MS, and on-line LC−MS analysis of metabolites generated from rat liver ...

Mass Spectrometry of Polymers

Abstract: Preface, G. Montaudo and R.P. Lattimer Introduction to Mass Spectromety of Polymers, M.J. Polce and C. Wesdemiotis Polymer Characteriztion Methods, G. Montaudo and M.S. Montaudo Pyrolysis Gas Chromatography/Mass Spectrometry (Py-GC/MS), S. Tsuge and H. Ohtani Electrospray Ionization (ESI-MS) and On-Line Liquid Chromatography/Mass Spectrometry (LC/MS), L. Prokai Direct Pyrolysis into the Ion Source (DPMS), G. Montaudo and C. Puglisi Field Ionization (FI-MS) and Field Desorption (FD-MS), R. P. Lattimer Fast Atom bombardment (FAB-MS), G. Montaudo and F. Samperi Time-of-Flight Secondary Ion Mass Spectrometry (FT-MS), S.J. Pastor and C.L. Wilkins Laser Fourier Transform Mass spectrometry (FT-MS), S.J. Pastor and C.L. Wilkins Matrix-Assisted Laser Desorption/Ionizationi Mass Spectrometry (MALDI-MS), G. Montaudo, M.S. Montaudo, and F. Samperi Two-Step Laser Desorption Mass Spectrometry, M.S. deVries and H.E. Hunziker

Identification of protein-bound carbohydrates by mass spectrometry.

Abstract: This review outlines the use of modern methods of mass spectrometry, mainly based on electrospray ionization and matrix-assisted lased desorption/ionization, for the identification of protein-bound carbohydrates. The techniques are briefly described together with methods for glycan release and purification prior to mass spectrometry. Fragmentation of glycans, produced under various conditions, is described in the context of obtaining structural information at the sensitivity required for proteomic work.