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M L Vestal

Publications and source records attributed to M L Vestal.

At least 19 recordsLinked to original sources
PubMed2000

The characteristics of peptide collision-induced dissociation using a high-performance MALDI-TOF/TOF tandem mass spectrometer.

A new matrix-assisted laser desorption/ionization (MALDI) time-of-flight/time-of-flight (TOF/TOF) high-resolution tandem mass spectrometer is described for sequencing peptides. This instrument combines the advantages of high sensitivity for peptide analysis associated with MALDI and comprehensive fragmentation information provided by high-energy collision-induced dissociation (CID). Unlike the postsource decay technique that is widely used with MALDI-TOF instruments and typically combines as many as 10 separate spectra of different mass regions, this instrument allows complete fragment ion spectra to be obtained in a single acquisition at a fixed reflectron voltage. To achieve optimum resolution and focusing over the whole mass range, it may be desirable to acquire and combine three separate sections. Different combinations of MALDI matrix and collision gas determine the amount of internal energy deposited by the MALDI process and the CID process, which provide control over the extent and nature of the fragment ions observed. Examples of peptide sequencing are presented that identify sequence-dependent features and demonstrate the value of modifying the ionization and collision conditions to optimize the spectral information.

Arginine↗
PubMed1997

Accurate mass measurements using MALDI-TOF with delayed extraction.

Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry is now an essential tool in biopolymer analysis. Sensitivity and mass range are unsurpassed, but mass measurement accuracy and resolution have been limited. With delayed extraction and a reflecting analyzer, mass measurements using MALDI-TOF can be made with an accuracy of a few parts per million (ppm). It is possible to distinguish Lys from Gln in peptides, and to determine the elemental composition of smaller molecules (mass 100-500). In database searching strategies, a smaller mass window, resulting from an increase in mass accuracy, greatly decreases the number of possible candidates. Mass measurement accuracy with errors less than 5 ppm is demonstrated on a mixture of 12 peptides ranging in mass from ca. 900 to 3700 Da. Mass measurements on 13 peaks in an unseparated tryptic digest of myoglobin gave results with an overall average error less than 3.5 ppm, with a maximum error of 7 ppm.

Adrenocorticotropic Hormone↗
PubMed1996

Element- and isotope-specific detection for high-performance liquid chromatography using chemical reaction interface mass spectrometry.

We have developed a combination of high-performance liquid chromatography (HPLC) and the chemical reaction interface mass spectrometry (CRIMS) method by using a Vestec Universal Interface (UI). This interface provides the extremely high degree of solvent removal that the CRIMS process requires. In doing so, we have produced an HPLC detector with the ability to carry out the element- and isotope-selective analyses with detection that is inherently: linear, structure-independent, sensitive, selective, comprehensive and flexible. The characteristics of the instrumentation and its performance are described.

Chromatography, High Pressure Liquid↗
PubMed1996

Applications of delayed extraction matrix-assisted laser desorption ionization time-of-flight mass spectrometry to oligonucleotide analysis.

A delayed ion extraction technique is shown to dramatically improve mass resolution and the overall quality of matrix-assisted laser desorption ionization (MALDI) mass spectra of oligonucleotides. Isotope limited mass resolution was obtained on samples up to 10-kDa molecular mass in linear mode, and as high as 7500 mass resolution (defined at half peak height) was observed in reflector mode. This performance is as good as that achieved to date for peptides and proteins. Applications included the detection of oxidized byproducts of phosphorothioate DNA and separation of components differing only by 15 Da at 9.5-kDa molecular mass. In addition to single components, complex mixtures could also be analyzed at greatly improved performance over conventional MALDI. An example is shown for sequence verification of an oligonucleotide of 31 bases in length by analyzing the failure products. Mass accuracy was adequate to verify sequences of oligodeoxyribonucleotides up to 9500-Da molecular mass. Fast fragmentation taking place between the ionizing pulse and the extraction pulse is demonstrated to be a sequencing tool for small oligonucleotides. By proper selection of matrix material, wavelength, and irradiance, fast fragmentation can be promoted efficiently. Fragment ions tend to form from cleavage of phosphodiester bonds, as previously observed in infrared MALDI.

Base Sequence↗
PubMed1995

Quantitation of metal isotope ratios by laser desorption time-of-flight mass spectrometry.

Laser desorption time-of-flight mass spectrometry (LD/TOF-MS) is evaluated for the determination of stable metal isotope ratios. The isotope ratios of five metal ions (Cu, Ca, Mg, Fe, Zn) in atomic absorption standard solutions and two metal ions (Ca, Mg) in human serum samples are determined. With an existing LD/TOF-MS instrument we show that the technique can overcome the difficulties of the most commonly used methods for measuring metal isotope ratios: (1) all metals are ionizable without surface treatment, thus overcoming the major drawback of thermal ionization mass spectrometry (TIMS); (2) there is no matrix involved to interfere with the metal ion detection, thus overcoming the major disadvantage of inductively coupled plasma mass spectrometry (ICPMS); (3) there is no interference from hydride ions, a major disadvantage of fast atom bombardment secondary ionization mass spectrometry; (4) a mixture of metals can be detected simultaneously using a single laser wavelength, overcoming the major disadvantage of resonance ionization mass spectrometry; (5) accuracy and precision comparable to ICPMS can be achieved with the current instrumentation; (6) precision comparable to TIMS is feasible; and most importantly (7) high precision can be achieved on very small quantities of material because the LD/TOF-MS instrument permits all masses to be monitored simultaneously and very small differences in isotope ratio can be detected.

Calcium↗
PubMed1995

Particle size distribution is not the major factor explaining variable analyte transmission efficiency in liquid chromatography/particle beam/mass spectrometry.

We characterized the particle size distribution and the analyte transmission efficiency of a liquid chromatography/particle beam/mass spectrometry (LC/PB/MS) system as a function of experimental variations normally used to optimize the LC/PB/MS system. The particle size distribution was evaluated using an electrical differential mobility particle sizer (DMPS) and both the DMPS and the mass spectrometer were used to evaluate transmission. The latter results were correlated to provide evidence related to mechanisms which contribute to poor sample transmission. Addition of ammonium acetate buffer did not increase the aerosol particle mean diameter. However, it did lead to significant increases in caffeine transmission efficiency observed in both the DMPS and the mass spectrometer. Our results were interpreted to suggest a possible electrostatic cause for quantitative anomalies in LC/PB/MS rather than simple mass discrimination in the particle beam momentum separator.

Aerosols↗
PubMed1995

AC corona-discharge aerosol-neutralization device adapted to liquid chromatography/particle beam/mass spectrometry.

An AC corona-discharge device was inserted upstream of a thermospray vaporizer tip in a liquid chromatography/particle beam mass spectrometer to neutralize static aerosol charging. Response of a test analyte was measured with or without discharge initiation. If the solvent contained no ammonium acetate buffer, increased analyte signal was associated with the discharge. However, in the presence of ammonium acetate the benefit of AC discharge neutralization was either not observed or was more subtle. This led to the conclusion that the previously observed ammonium acetate "carrier" effect is attributable, at least in part, to neutralization of static electric charges produced spontaneously during the solvent nebulization process. In a second experiment, the pattern of particles issuing from the system momentum separator was examined by aiming the particle beam at a cold target located within a mass spectrometer ion source. Variations in particle density were observed depending on (i) whether or not the aerosol had been neutralized and (ii) the proximity of electron-beam-collimating magnets to the particle beam trajectory. These results are consistent with a hypothesis that electrostatic charging occurs spontaneously during the nebulization process in which an aerosol is formed from the high performance liquid chromatography effluent. Such electrostatic charging introduces a factor likely to degrade system performance by at least two modes: through interactions of the charged aerosol particles (i) with the walls of the aerosol transmission pathway, and, after they are accelerated into a particle beam and introduced into the mass spectrometer, (ii) with the magnets used for electron beam collimation in many mass spectrometer ion sources.

Acetates↗
PubMed1988

Tandem mass spectrometric studies of the fragmentation of penicillins and their metabolites.

The fragmentation of two penicillins, ampicillin and amoxicillin, and their principal metabolites has been studied by a combination of liquid chromatography/thermospray mass spectrometry and tandem mass spectrometry. A high-resolution tandem mass spectrometer was used to obtain chemical ionization, fast-atom bombardment, and collision-induced dissociation mass spectra. Structural information and fragmentation mechanisms have been deduced from ions in the mass and collision spectra. This knowledge is useful in the analysis and identification of metabolites of ampicillin and related drugs in human body fluids.

Ampicillin↗
PubMed1988

Pharmacokinetics of Amonafide in dogs.

Amonafide, one of a series of imide derivatives of 1,8-naphthalic acid synthesized by Brana et al. has shown significant antitumor activity against a variety of experimental tumors, including L1210 leukemia and P388 leukemia. Along with the clinical trial at our institute, we have studied the disposition of Amonafide in dogs by HPLC and fluorometry. Six dogs received Amonafide i.v. at 5 mg/kg (100 mg/m2) over 15 min; three were sacrificed at 6 h, and three at 24 h. The initial plasma t1/2 of Amonafide was 2.4 +/- 0.4 min, the intermediate t1/2, 26.8 +/- 3.7 min, and the terminal t1/2, 21.7 +/- 4.0 h. The peak plasma concentration achieved was 6.3 +/- 1.7 micrograms/ml. The average apparent volume of distribution was 12.84 +/- 0.54 1/kg, and the total clearance was 0.56 +/- 0.16 1/kg/h. In 24 h, 9.5% +/- 0.2% of the administered dose was excreted in the urine as the parent drug, and 7.4% +/- 1.4% in the bile in 6 h. Amonafide penetrated the CSF readily and achieved the highest concentration 20-25 min after administration, which was 30% of the concurrent plasma level. Amonafide underwent extensive metabolism to at least three major metabolites and two or more minor metabolites. The alpha and beta plasma t1/2 of the major metabolite, an N-oxide derivative, were 24.8 min and 28.6 h, respectively. The 24-h cumulative urinary excretion was 1.4% of the injected dose, and the cumulative biliary excretion was 16.7% in 6 h. At autopsy 6 h after dosing, the liver contained the highest percentage (0.23% of administered dose) of unchanged Amonafide, followed by the stomach (0.11%), lung (0.04%), kidney (0.04%), and pancreas (0.03%). The rest of the major organs retained less than 0.02% of the Amonafide dose. One day after dosing, no detectable amount of Amonafide was found in any of these tissues, indicating that Amonafide appears to be extensively metabolized and not significantly retained in the dog.

Adenine↗
PubMed1985

Thermospray liquid chromatography-mass spectrometry of nucleosides and of enzymatic hydrolysates of nucleic acids.

Nucleosides dissolved in aqueous buffered solutions undergo ionization during direct introduction of the solution into a mass spectrometer using a thermospray interface. The principal ions formed represent the protonated molecule, the corresponding protonated free base, and sugar. In addition to potential utility for characterization of new nucleosides, the technique can be used to monitor nucleosides separated from enzymatic hydrolysates by liquid chromatography. The selectivity of chromatographic detection is significantly greater than with UV absorbance alone so that independent detection of components of unresolved chromatographic peaks is usually possible. Detection limits, with signal/noise greater than 10 for most nucleosides, are approximately 0.1-1 ng per component for selected ion monitoring and 10-50 ng for full-scan mass spectra. Examples are given from the detection of modified nucleosides in enzymatic hydrolysates of 0.05 A260 units (2.5 micrograms) of rabbit liver tRNAVal and of unfractionated H. volcanii tRNA.

Aerosols↗
PubMed1984

High-performance liquid chromatography-mass spectrometry.

Techniques for on-line coupling of high-performance liquid chromatography with mass spectrometry are reviewed with particular emphasis on those suitable for application to nonvolatile samples. The present status of various techniques is summarized and the strengths and weaknesses of the various approaches are assessed. The potential for future application of recently developed techniques for combined liquid chromatography and mass spectrometry is discussed.

Amino Acid Sequence↗
PubMed1984

Direct monitoring of sequential enzymatic hydrolysis of peptides by thermospray mass spectrometry.

A procedure for peptide sequencing using an immobilized exopeptidase column directly coupled to a thermospray mass spectrometer is described. The amino acids sequentially released from the C-terminus of the peptide chain are directly introduced into a thermospray ion source by a flowing aqueous buffer. The buffer is essential for the direct production of ions from solution. The method eliminates the need to derivatize the amino acids for detection and, by comparison to standard injections, amino acid sequence information can be obtained in less than two minutes. With the present configuration, detection limits are typically in the low picomolar range.

Amino Acid Sequence↗