Showing papers in "Rapid Communications in Mass Spectrometry in 1995"

Delayed extraction matrix‐assisted laser desorption time‐of‐flight mass spectrometry

Abstract: A new delayed extraction matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometer system is described which provides dramatically improved performance over that obtained with identical TOF analyzers operated with constant electrical fields In this system the ions formed by MALDI are produced in a weak electrical field, and subsequently extracted by application of a high voltage pulse after a predetermined time delay Three parameters can be independently adjusted to optimize the performance These include the field magnitude and direction during and immediately following ion production, the magnitude of the extraction field, and the time delay between the laser pulse and application of the extraction field Theoretical equations are presented which guide the selection of these parameters to optimize the performance Results are presented from three TOF analyzers of similar design, but ranging in size from a 13 m linear analyzer to a 64 m reflector In all cases delayed extraction provides substantially improved resolution over that obtained from static operation In the smallest linear analyzer resolution of M/ΔM (full width at half maximum) of 4000 is demonstrated for angiotensin I, and with the largest reflecting analyzer, the isotope peaks of bovine insulin are resolved nearly to baseline With larger proteins, the isotopic peaks are not resolved, but resolution approaching the width of the isotopic envelope is obtained Resolution improvement is demonstrated for proteins up to 30 kDa In addition to improved resolution, delayed extraction is shown to improve the quality of MALDI mass spectra by suppressing matrix background, reducing chemical noise, and minimizing the effect of laser intensity on performance

Molecular Weight Determination of Megadalton DNA Electrospray Ions using Charge Detection Time-of-Flight Mass Spectrometry

Abstract: We present results obtained with a novel mass spectrometer capable of determining the mass of multiply charged electrospray ions generated from samples of macromolecules in the megadalton (MDa) size range. The instrument utilizes a sensitive amplifier which can detect the charge on a single ion as it passes through a tube detector. A velocity measurement of an ion with known electrostatic energy provides the ion's mass-to-charge ratio. Simultaneous detection of the ion charge permits a mass assignment to be made for each ion. Electrospray ions of DNA and polymer molecules with masses greater than 1 x 10(6) Da and charge numbers (z) in excess of 425 e(-) are readily detected in this mass spectrometer. The weights of small particles were also measured. The on-axis single-ion detection configuration provides a duty cycle of nearly 100% and extends the practical application of electrospray mass spectrometry to the analysis of very large molecules with relatively inexpensive instrumentation.

Characterization of polymers by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry: Molecular weight estimates in samples of varying polydispersity

Abstract: Matrix-assisted laser desorptionhonization time-of-flight mass spectrometry (MALDI-TOF MS) allows the detection of large molecules such as those present in synthetic and natural macromolecules. Synthetic polymers may show a wide range of molecular weight distributions (MWD), according to the synthetic method used in their preparation. We have studied several poly(methylmethacry1ate) (PMMA), poly(styrene) (PS) and poly(ethyleneg1ycol) (PEG) samples with varying MWD, and also a number of condensation polymers such as Nylon-6, poly(carbonate) and poly(ester). Measurements of MALDI-TOF spectra in the linear mode were used in our work to estimate the molecular weight (MW) and MWD of the polymer samples. Our results show that the molecular weight estimates provided by MALDI-TOF measurements agree with the values obtained by conventional techniques, such as gel-permeation chromatography (GPC), only in the case of polymer samples with very narrow molecular weight distribution. However, when the polydispersity reaches values around 1.10 the difference between the MW measured by GPC and measured by MALDI may amount to up to about 20%. At higher dispersions, the MALDI spectra fail to yield reliable MW values.

Utility of organic bases for improved electrospray mass spectrometry of oligonucleotides

Abstract: The sensitivity and accuracy of the mass spectrometric analysis of oligonucleotides using electrospray ionization can be compromized when the oligomer is adducted in the gas phase to cations such as sodium or potassium. We have evaluated the addition of mM concentrations of a series of organic bases with solution pKb values ranging from 11.5 to 5.5 and gas-phase proton affinities ranging from 213 to 232 kcal/mol as a method for suppression of signals from alkali-adducted ions. Stronger bases such as triethylamine and piperidine reduce the signals from bound sodium most effectively, but also decrease the total ion current from oligonucleotide. Imidazole, with a solution pH of ∼8.0, provides modest suppression of sodium/potassium adduct ions, but up to a four-fold improvement in sensitivity. Co-addition of imidazole and triethylamine or piperidine produces high ion abundance and good suppression of cation-adducted species for samples of phosphodiester or phosphorothioate oligomers which have not been desalted via preliminary precipitation or by high-performance liquid chromatography. Addition of high concentrations of imidazole generates a bimodal distribution of charge states, which may reflect different gas-phase conformations for single-stranded oligomers.

Matrix‐assisted laser desorption/ionization mass spectrometry: Improved matrix for oligosaccharides

Abstract: The aim of this article was to study the influence of different matrix molecules on the quality of matrix-assisted laser desorption/ionization mass spectra of oligosaccharides. An important criterion was the sample preparation, i.e. the crystallization process leading to the matrix from which the analytes were desorbed and investigated. Quality criteria were, among others, the resulting molecular peak intensity, the mass resolution, and the suppression of unwanted matrix peaks. It was found that a mixture of 2,5-dihydroxy benzoic acid (DHB) and 1-hydroxy isoquinoline (HIC) in a weight ratio of 3:1 was best suited for the analytical investigation of oligosaccharides. In addition, this matrix mixture was found to be quite tolerant against all kinds of buffers, salts, and even additives such as sodium dodecyl sulfate (SDS). Furthermore, we determined the different affinities of the alkaline metals to the carbohydrates and found that cesium and potassium ions ionize oligosaccharides about three times better than sodium ions and therefore have an important influence on the quantum yield.

Ion exchange and purification of carbohydrates on a Nafion® membrane as a new sample pretreatment for matrix-assisted laser desorption/ionization mass spectrometry

Abstract: A Nafion membrane was tested as a new tool for a fast and easy sample pretreatment for matrix-assisted laser desorptionlionization mass spectrometry (MALDI-MS) measurements. This membrane material was used for ion exchange and carbohydrate purification with minimal quantities of sample solution. An ion exchange method for carbohydrates was developed and demonstrated on a Dextran sample. The cations of the original sample were replaced within minutes by potassium or cesium ions. Another feature of this membrane was the fact that proteins and peptides adsorb on the acid surface. This behavior was investigated as a purification step for carbohydrates with high peptide and protein impurity concentrations. It was found that oligosaccharide libraries from rat- and mouse IgG mass spectra can be obtained clearly in the presence of high peptide impurities. Since the introduction of matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS), this method has been developed into a fast and sensitive analytical technique. 'L' Especially for peptides and proteins, MALDI is the method of choice to get mass information. Another feature is the low quantity of sample solution that is needed for a MALDI investigation. Sometimes however , measurements become difficult because of high salt or buffer concentrations and the presence of certain impurities. The right choice of matrix and additives can improve these measurements, but this approach is limited to just a few applications. Another way of solving the problem is sample

Application of the fast-evaporation sample preparation method for improving quantification of angiotensin II by matrix-assisted laser desorption/ionization

Abstract: The fast-evaporation method of sample preparation has been applied for quantitative analysis using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. An instrumental protocol focusing on improvement of shot-to-shot repeatability and compensation for signal degradation has been developed for quantification of angiotensin II using the fast-evaporation technique and an internal standard. The fast-evaporation method was compared to the standard method of sample preparation (using a multicomponent matrix) in the quantitative analysis of angiotensin II, and found to be superior in several respects. Improvement in sample homogeneity using the fast-evaporation method enhanced both point-to-point repeatibility and sample-to-sample reproducibility. The relative standard deviations of the analyte/internal standard ratios (point RSD) were decreased by a factor of three compared to those obtained using the multicomponent matrix method. The average point RSD was found to be ca. 5% for the fast-evaporation technique. Two internal standards were evaluated for quantification of angiotensin II. The better one, 1-SAR-8-Ile angiotensin II, yielded a relative standard deviation of the standard curve slope of ca. 2.2% over two orders of magnitude of concentration (45 nM to 3000 nM), an improvement by a factor of two over the standard preparation method. Renal microdialysate samples, spiked with angiotensin II and the internal standard 1-SAR-8-Ile angiotensin II, were also analyzed using the fast-evaporation technique. The detection limit was calculated to be in the high attomole range (675 amol). Furthermore, the accuracy for a single determination of angiotensin II concentration in these samples was found to be 13.9% with a relative error of 8.19%.

Molecular weight distribution of poly(dimethylsiloxane) by combining matrix-assisted laser desorption/ionization time-of-flight mass spectrometry with gel-permeation chromatography fractionation

Abstract: Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) allows detection of large molecules such as those present in synthetic and natural macromolecules. Until recently, it was reported that MALDI-TOF measurements can provide correct molecular weight (MW) estimates only for nearly monodisperse polymer samples. We have now developed a methodology for polydisperse samples. We recorded the gel-permeation chromatography (GPC) trace of a polydisperse polymeric sample of poly(dimethylsiloxane) (PDMS), collecting 42 fractions. Selected fractions were analyzed by MALDI-TOF and the average MW of each fraction was determined, allowing a calibration of GPC curves against absolute MW. The calibrated GPC trace was then used to compute average MW and molecular-weight distribution (MWD) of the unfractionated poly(dimethylsiloxane) sample. In the spectra of low molecular-weight fractions, the resolution is high enough to resolve the contributions of the various PDMS oligomers as separate signals.

Matrix‐assisted laser desorption/ionization mass spectrometry of polysaccharides

Abstract: In this paper we report matrix-assisted laser desorption/ionization (MALDI) mass spectra of dextrans up to 100 000 Da molecular weight and compare these measurements with those obtained by conventional size-exclusion chromatography with low-angle laser light scattering (SEC/LALLS). These results extend the usefulness of MALDI-MS to higher molecular weight polysaccharides and give some insights into the MALDI process.

Direct database searching with MALDI‐PSD spectra of peptides

Abstract: The analysis of matrix-assisted laser desorption ionization post-source decay (MALDI-PSD) mass spectra of peptides by using the cross-correlation method for database searching is illustrated. MALDI-PSD mass spectra are shown to contain sufficient fragmentation information to uniquely identify the correct amino acid sequence from large protein databases (approximately 160,000 entries). A search employing the MALDI-PSD mass spectrum of a phosphorylated peptide that correctly identifies the amino acid sequence and the site of phosphorylation is also illustrated.

Pyrolysis/gas chromatography/mass spectrometry of lignocellulose

Abstract: The use of pyrolysis/gas chromatography/mass spectrometry (PY/GC/MS) to determine the molecular composition of lignocellulose is reviewed and the technique illustrated with applications on some novel systems Constituents and structural arrangement of lignocellulosic polymers in plant cell wall are briefly described The basic principles of pyrolysis and the main advantages and disadvantages of PY/GC/MS are discussed PY/GC/MS analyses of (a) paper industry effluents, (b) agricultural by-products subjected to biological processes of delignification and (c) recycled paper are presented as examples of the amount of information that PY/GC/MS can provide on lignin classification and monitoring of delignification treatments as well as on the fingerprinting of lignocellulosic materials The ion trap detector mass spectra of 56 pyrolysis products of lignocellulose, including compounds of phenolic, furanic and pyranic nature, are shown

Molecular mass measurement of polymerase chain reaction products amplified from human blood dna by electrospray ionization mass spectrometry

Abstract: We report here on the first analysis of polymerase chain reaction (PCR) products amplified from a small amount of human blood DNA by electrospray ionization mass spectrometry (ESI-MS). Adenomatous polyposis coli (APC) gene fragment of about 50 base pairs (bp) with a relative molecular mass (M(r)) of approximately 15,000 u was amplified from human blood DNA by PCR. The accurate molecular mass of the PCR products was determined with an accuracy of approximately 0.005% by ESI-MS. The amount of DNA used was only 100 ng (approximately 50 zmol; the theoretically required amount of blood is therefore less than 1 microliter for PCR). The ESI-MS measurement of the PCR products proved to be a new accurate, sensitive and fast tool for gene diagnosis.

Effects of solvent composition on molecular ion response in electrospray mass spectrometry: Investigation of the ionization processes

Abstract: Electrospray ionization of four structurally diverse natural products, actinomycin D, digitoxin, reserpine and quercetin was investigated. Specific attention was paid to the molecular ions formed under typical reversed-phase high-performance liquid chromatography (RP-HPLC) conditions. The response characteristics of [M + H]+, [M + NH4]+ and [M + Na]+ Ions, observed upon addition of formic acid, ammonium formate and sodium acetate were studied. It was found that the highest response for these molecular ions was obtained with proton, ammonium and sodium ion concentrations of approximately 10−3 ∼ 10−4 M. This critical concentration appears to be correlated with the equilibrium between the thermodynamically controlled molecular ions in solution and electrospray produced gas-phase ions. Gas-phase ion reactions in the ion transfer region were investigated for digitoxin, and the mechanism of gas-phase ion formation is briefly discussed.

A combined magnetic sector-time-of-flight mass spectrometer for structural determination studies by tandem mass spectrometry

Abstract: A combined magnetic sector–time-of-flight instrument has been constructed and used with both continuous (liquid secondary ion mass spectrometry and electrospray ionization) and pulsed (matrix-assisted laser desorption/ionization) ion sources. The design includes provision for both low- and high-energy gas collision induced decompositions and orthogonal acceleration of the product ions into the time-of-flight mass analyser. Tandem mass spectra may be acquired for singly and multiply charged precursor ions and reliable mass measurements are easily obtained. Product-ion mass spectra are quite reproducible regardless of any instability in the precursor ion beam intensity.

Utility of matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry for the analysis of low molecular weight compounds

Abstract: A range of low molecular weight compounds (<800 Da) have been examined by matrix-assisted laser desorption time-of-flight mass Spectrometry to demonstrate the general analytical utility of this technique. The compound classes investigated included: carbohydrates, quaternary ammonium salts, sterols, nucleosides, purine and pyrimidine bases, amino acids, catecholamines, opioids, antibiotics, prostaglandins and a range of macrocyclic metal complexes of porphyrins and phthalocyanines. Many of the compounds tested are of biochemical, geochemical, industrial and/or therapeutic interest. Most organic analytes gave intense protonated molecules, but some were characterized by sodium adduct ions (i.e., [M + Na]+). The metal-containing compounds formed radical-cation molecular ions. In all instances the ions detected could be assigned, and excellent agreements between calculated and experimental mass values were obtained.

7-deaza purine bases offer a higher ion stability in the analysis of dna by matrix-assisted laser desorption/ionization mass spectrometry

Abstract: Oligodeoxynucleotides which contain 7-deaza analogues of the normal purine nucleotides have been synthesized both enzymatically and chemically. When subjected to matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analysis, the modified samples offer both higher stability and increased sensitivity compared to otherwise identical unmodified oligodeoxynucleotides. In view of these observations, models for the fragmentation of oligodeoxynucleotides in MALDI-MS with positive ion detection mode are presented. Additionally, the potential use of 7-deaza purine nucleotides in the MALDI-MS analysis of DNA sequencing reactions is discussed.

Quantitative analysis of cytokinins by electrospray tandem mass spectrometry

Abstract: A methodology was developed for the analysis of cytokinins from plant tissue using electrospray tandem mass spectrometry in combination with HPLC. A detection limit of 1 pmol zeatin-riboside injected on-column was achieved under multiple reaction monitoring conditions. Linearity was observed within a concentration range of 1–100 pmol injected on-column. In view of the analysis of a considerable amount of samples, the chromatographic conditions were selected which were a compromise between speed of analysis and resolution. This approach, in combination with multiple reaction monitoring, allowed the analysis of up to 150 samples a day, and quantitation of 16 different cytokinins per sample.

Thermal decomposition kinetics of protonated peptides and peptide dimers, and comparison with surface-induced dissociation.

Abstract: Rate constants for the unimolecular decomposition of peptide monomer and dimer ions by thermal and surface-induced dissociation (SID) are measured and compared. Rate constants for thermal dissociation are measured in a heated wide-bore capillary flow reactor attached in front of the capillary leading into the mass spectrometer. Thermal decomposition of the leucine enkephalin ion (YGGFL)H+ is observed between 600 and 680 K with rate constants of 20-200 s-', and yields many of the same fragments as SID at 35 eV, although with different relative intensities. The thermal decomposition yields the Arrhenius parameters E,, = 38.3 kcal/mol, log A = 15.7. The decomposition of the monomer and dimer ions are also observed by using SID on C18 and fluorinated hydrocarbon surfaces, with rate constants of 2 X lo4 to 40 X lo4 s-'. The SID activated monomer ions are assigned equivalent temperatures of 710-840 K by extrapolation of the thermal activation parameters. The protonated dimer ion (YGGFL)2 H+ decomposes thermally at 500-540 K to yield the monomer ion. The dimer also decomposes by SID at low collision energies 10-20 eV on both surfaces to yield the monomer ion, and at much higher energies of 60-80 eV to yield fragments identical to the decomposition of the monomer. The large energy requirement for fragmentation from the dimer is due to energy deposition into more degrees of freedom plus the additional energy required for dissociation of the dimer to the monomer. It is assumed that the energy deposition is linear with collision energy up to 80 eV, and that the energy becomes randomized throughout the dimer, including energy flow through the hydrogen bond($. These mechanistic assumptions are supported quantitatively by the SID energy relations between monomer and dimer fragmentation. Thermal decomposition of the larger, multiply protonated melittin ion [M + 3HI3+ occurs at substantially higher temperatures, between 810-840 K, than those required for thermal decomposition of (YGGFL)H+, to yield many of the same sequence ions as produced by SID at 135 eV on a fluorinated surface. The fragmentation of molecular ions or protonated molecules is essential for mass spectrometric structure determination, while the decomposition of gas-phase adducts may allow the determination of non-covalent binding energies. We previously studied the thermal decomposition kinetics of carbonium ions and protonated alcohols and ethers,'-4 and the thermal decomposition of non-covalent , hydrogen-bonded dimers is observed routinely in the reverse processes of clustering equilibria. This work extends unimolecular kinetics to larger biomolecules. A similar application was presented more recently by Busman et al. for the decomposition of melittin ions.' The present work also extends previous work of the authors in ion pyrolysis and surface-induced dissociation (SID) to compare the energetics of these two processes. Surface-induced dissociation, developed originally by Cooks and coworkers,6 has proved to be a powerful technique for the investigation of the mass spectral fragmentation of protonated pep tide^."'^ In addition to practical applications, e.g. sequencing peptides, SID has the potential to provide energetic data that can be used to describe the mechanisms of peptide fragmentation. We have recently reported, for example, that fragmentation efficiencies (% fragmentation vs. collision energy) can be correlated with the basicities of peptides and with peptide size.13 Although these qualitative trends are themselves important , it is desirable to

Comparison of fragmentation modes for the structural determination of complex oligosaccharides ionized by matrix‐assisted laser desorption/ionization mass spectrometry

Abstract: Fragment ions from underivatized N-linked oligosaccharides ionized by matrix-assisted laser desorption/ionization mass spectrometry were obtained by spontaneous fragmentation on a magnetic sector mass spectrometer, by post-source decay (PSD) on a reflectron time-of-flight (TOF) instrument and by collision-induced dissociation on a magnetic sector instrument fitted with an orthogonal-TOF analyser. Spontaneous fragmentation on the magnetic sector instrument produced ions mainly by glycosidic cleavage together with two abundant ions formed by cross-ring cleavage of the reducing-terminal residue. The PSD spectra were similar, the majority of ions being formed by glycosidic cleavage. Internal fragment ions were abundant. High-energy collision-induced dissociation spectra, recorded with the orthogonal-TOF analyser, differed considerably from the other types of spectra, particularly in the appearance of major fragment ions produced by cross-ring cleavages of most of the constituent monosaccharide residues. These ions allowed much sequence and branching information to be obtained from the oligosaccharide.

Detection of high molecular weight starburst dendrimers by electrospray ionization mass spectometry

Abstract: An entire series of Starburst polyamidoamine (PAMAM) dendrimers consisting of generations 1 through 10 (G1–10) have been studied by positive-ion electrospray ionization mass spectrometry (ESI-MS) using an extended m/z range quadrupole mass spectrometer. Charge-state distributions were detected as high as m/z 12 000 for the generation 10 dendrimer, having a theoretical molecular weight of 1 megadalton and containing approximately 93 maximum positive charges on the molecule. Accurate molecular weight determinations of the smaller generation dendrimers (G1–3, Mr ∼ 1.4kDa to 6.9kDa) were obtained using a commercial triple quadrupole instrument. The unit resolution ESI mass spectra provide information on the number of incomplete reactions which may occur during polymer synthesis. The extent of gas-phase charging observed by ESI-MS on the entire series of macromolecules was found to exhibit a linear relationship to M, consistent with theoretical models prediciting a spherical ion structure with maximum charging controlled by Coulombic effects.

Rapid screening of genetic polymorphisms using buccal cell dna with detection by matrix-assisted laser desorption/ionization mass spectrometry

Abstract: A new approach is developed for the rapid and cost-effective detection of human genetic polymorphisms based on matrix-assisted laser description/ionization mass spectrometric (MALDI MS) detection using a nitrocellulose film substrate. This method employs polymerase chain reaction (PCR) amplification using DNA extracted from buccal cells as templates, followed by direct digestion with restriction enzymes and subsequent analysis by MALDI MS. The extraction of DNA from buccal cells provides a rapid and convenient means for sampling PCR-based diagnostic analysis. The amount of DNA was sufficient as the template for both normal PCR amplifications, and amplifications involving the use of mismatched primers and multiple primers. The MALDI MS methodology has been successfully used for the analysis of such PCR products where restriction fragments generated directly in PCR reactions have been used for detection of carbonic anhydrase and cystic fibrosis transmembrane conductance regulator as model genes. The detection of genetic polymorphisms following routine biological and clinical procedures with the MALDI MS method is demonstrated. The results from MALDI MS analysis are shown to be comparable to those obtained from gel electrophoresis but the MALDI MS method is several orders of magnitude faster than gel electrophoretic techniques. The method described herein should also be readily extended to other areas involving DNA screening and testing.

Analysis of enzymatic DNA sequencing reactions by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry

Abstract: The products from base-specific, dideoxy-nucleotide chain-termination DNA sequencing reactions catalyzed by the modified T7 DNA polymerase have been analyzed by using the technique of matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry. Preliminary experiments were performed to determine detection limits for a synthetic mixture of mixed-base single-stranded DNA which contained a 14-mer, a 21-mer, and a 41-mer; acceptable spectra, showing peaks for each component, were obtainable for samples that contained as little as 5 fmol per component. Initial sequencing reactions were therefore carried out on 2-pmol amounts of a short synthetic template that was 45 nucleotides in length, employing 2 pmol of 12-mer as the primer strand. This provided readable sequence information out to the 19th base past the primer. Using a 21-mer primer, nearly the entire sequence of the template could be read.

Sensitive detection and structural characterization of trimethyl(p-aminophenyl)-ammonium-derivatized oligosaccharides by electrospray ionization-mass spectrometry and tandem mass spectrometry.

Abstract: Mass spectrometric methodologies which use electrospray ionization (ESI) for oligosaccharide structural determination and which are linked to classical procedures, such as reductive amination, have been established. Several derivatives of a model oligosaccharide were prepared and their ionization efficiencies in electrospray ionization (ESI) and fast-atom bombardment (FAB) mass spectrometry were investigated. The trimethyl-(p-aminophenyl)ammonium (TMAPA) derivatives showed extremely high sensitivity in positive-ion ESI-MS and gave Y- and Z-series sequence ions by ESI tandem mass spectromety (MS/MS). This study suggests that TMAPA-derivatized oligosaccharides used in ESI-MS and ESI-MS/MS would be effective for structural characterization of oligosaccharides that are available only in limited quantities.

Endgroup analysis of polyethylene glycol polymers by matrix-assisted laser desorption/ionization Fourier-transform ion cyclotron resonance mass spectrometry

Abstract: Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS) by external injection of matrix-assisted laser desorbed and ionized (MALDI) polymers offers good possibilities for characterization of low molecular weight homopolymers (MW range up to 10 kDa). The molecular masses of the molecular weight distribution (MWD) components of underivatized and derivatized (dimethyl, dipropyl, dibutyl and diacetyl) polyethylene glycol (PEG) 1000 and 4000 were measured by MALDI-FTICR-MS. These measurements have been performed using a commercial FTICR spectrometer with a home-built external ion source. MALDI of the samples with a 2,5-dihydroxybenzoic acid matrix in a 1000:1 matrix-to-analyte molar ratio produces sodiated molecules in a sufficient yield to trap the ions in the ICR cell. The masses of the molecular weight distribution of PEG components were measured in broad-band mode with a mass accuracy of < 5 ppm in the mass range around 1000 u and within 40 ppm accuracy around 4000 u. From these measurements, the endgroup mass of the polymer was determined by correlation of the measured component mass with the degree of polymerization. The masses of the PEG endgroups have been determined within a deviation of 3-10 millimass units for the PEG1000 derivatives and 10-100 millimass units for the PEG4000 derivatives, thus confirming the identity of the distal parts of the model compounds.

‘On‐line’ liquid chromatography/nuclear magnetic resonance mass spectrometry—a powerful spectroscopic tool for the analysis of mixtures of pharmaceutical interest

Abstract: Liquid chromatography (LC), simultaneously coupled with both nuclear magnetic resonance (NMR) and mass spectrometry (MS) ‘on-line’ is a powerful structural tool and has a potentially vast range of uses within the pharmaceutical industry. Data from a mixture of fluconazole and related triazoles have been obtained from an LC/NMR-MS system developed ‘in-house’, demonstrating the power of this novel analytical approach.

Inductive detector for time-of-flight mass spectrometers

Abstract: A mass spectrometer is disclosed having a detector that detects the induction of a charge as an ion pulse passes by the detector and provides a representative output signal thereof. The inductive detector output signal is present regardless of the presence or intensity of preceding ion pulses and also the inductive detector is relatively insensitive to the velocity of the charged particles being detected. Further, the inductive detector does not destroy the vast majority of the ion pulses that it detects so that the non-destroyed ion pulses may be further analyzed by spectrometers attached in tandem.

Bio-affinity characterization mass spectrometry.

Abstract: A new approach, bio-affinity characterization mass spectrometry (BACMS), aimed at providing a more rapid, sensitive and potentially more flexible alternative to techniques presently employed for the characterization of noncovalent interactions in mixtures, such as would be encountered in combinatorial chemistry, in presented. BACMS avoids some of the difficulties and potential artifacts associated with affinity chromatography since the noncovalent associations occur in solution; thus, BACMS avoids the requirement of solid support media and the development of non-interfering linker species. This paper describes the conceptual basis for the methodology and its potential use in applications which include the screening of high affinity ligands in support of new drug development. BACMS exploits new Fourier-transform ion cyclotron resonance (FTICR) mass spectrometry technologies which, when coupled to electrospray ionization (ESI), allow the investigation of specific noncovalent complexes formed in solution. BACMS utilizes the well-known attributes of FTICR, such as the high resolution mass analysis and (MS)n (n > or = 2) capabilities; however, it is even more directly a result of recently developed techniques involving quadrupolar excitation, such as selected-ion accumulation. These tools are demonstrated and the results illustrate the extraordinary sensitivity achievable (solution concentration of 1 x 10-9 M without the use of separations prior to ESI). Thus, the new capabilities demonstrated here, in conjunction with ESI, will be useful for the investigation of very low relative concentration noncovalent association directly from solution, and promote a faster alternative for combinatorial mixture screening and analysis.

A new hybrid mass spectrometer for the investigation of ion/molecule reactions

Abstract: An RF-only quadrupole collision cell, fitted with retardation and acceleration lenses, has been installed in a field-free region of a large-scale tandem mass spectrometer. This new arrangement has allowed decelerated, mass-selected ions (ca. 5 eV kinetic energy) to react with reagent gases and reaccelerated, mass-selected products (ca. 8 keV) to be subsequently identified by collisional activation mass spectrometry. The system was tested by looking at ion/molecule reactions of cyclobutanone molecular ions, previously studied by FTICR mass spectrormetry.

A reconciliation of mass ranges from matrix-assisted laser desorption/ionization mass spectrometry and size exclusion chromatography for coal-derived materials

Abstract: Size exclusion chromatography (SEC) has been used extensively in the characterization of coal-derived liquids to estimate molecular masses (MM), indicating the presence of considerably greater upper mass ranges compared to mass spectrometric methods based on heated probes and field ionization. In the present study, the use of tetrahydrofuran (THF), a solvent commonly used in SEC, has been shown to lead to partial loss of sample on column packings and to allow some separation by an adsorption mechanism rather than by size exclusion. In this paper, we have compared these results with data from SEC, where 1-methyl 2-pyrrolidinone was used as the mobile phase, indicating that the largest molecules (not observed in THF-based work) appear at the exclusion limit, with a continuum of material down to the total permeation limit of the column. In terms of polystyrene standard masses, this is equivalent to a range from 100 u, at the lower limit, up to in excess of 30–40 000 u and possibly over 2 000 000 u. Our results from SEC in NMP suggest that limitations exist in much solution-based work attempting to identify distributions of MMs in coal-derived liquids. Matrix-assisted laser desorption/ionization (MALDI) spectra of the fractions show similar features to those seen by SEC in NMP, with a continuum from high to low mass, and a significant shift to higher mass in the insoluble fraction compared with the soluble fraction. The new data are in line with observations by laser desorption mass spectrometry (LD-MS) and MALDI-MS, which have shown much greater upper-MM limits than either SEC (in THF) or mass spectrometric techniques relying on thermal evaporation of coal-derived materials from heated probes. The work would appear to have implications for other polydispersed natural polymer systems.