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At least 1,135 records · Page 63Linked to original sources
PubMed1997

Determination of the pesticide fenbutatin oxide in tomatoes, cucumbers and bananas by high performance liquid chromatographic/atmospheric pressure chemical ionization-mass spectrometry.

A rapid method, using high-performance liquid chromatography (HPLC)/ atmospheric pressure chemical ionization-mass spectrometry, has been developed for the determination of fenbutatin oxide in tomatoes, cucumbers and bananas. Samples were homogenized with sodium carbonate and ethyl acetate, filtered through sodium sulphate, concentrated and solvent exchanged into acetonitrile prior to analysis. HPLC was performed on a Hypercarb column with 10:90 acetic acid (5% v/v glacial acetic acid in water)/acetonitrile at a flow rate of 1 mL/min. Positive ionization selected-ion monitoring was performed on the 7 isotopic cluster ions from the tris(2-methyl-2-phenylpropyl) tin fragment. A comparison of solvent-based and extract-based standards showed that tomato and cucumber matrices had a slight enhancement effect on the signal intensity, whereas the banana matrix exerted a signal suppression effect. Calibration was linear over the range 0.25-5.0 ng/microL. The mean spike recoveries (extracts spiked at 0.5 mg/kg) were 88% for tomatoes and 80% for both cucumbers and bananas with relative standard deviations of 6%, 7% and 8% respectively. Limits of detection were commodity dependent and ranged from 0.06-0.12 ng/microL (equivalent to 0.01-0.02 mg/kg in the crop). Ionization was stable for long analytical time periods.

Chromatography, High Pressure Liquid↗
PubMed1997

Analysis of radiation induced nucleobase-peptide crosslinks by electrospray ionization mass spectrometry.

Upon exposure to ionizing radiation, DNA undergoes a variety of modifications including the production of a covalent bond between the nucleobase thymine and the amino acid tyrosine. These crosslinked lesions, produced in cells exposed to ionizing radiation, if unrepaired are thought to result in cell death. We have used electrospray ionization mass spectrometry (ESI-MS) to study a model system consisting of the peptide angiotensin, a 10 amino acid peptide containing only one tyrosine residue, irradiated in the presence of the nucleobase thymine. The presence of the covalently crosslinked species has been determined by ESI-MS, by the appearance of additional species in the irradiated samples which correspond to the adduction of thymine as well as a hydrated species containing thymine and water (5-hydroxy-6-hydrothymine). The formation of 5-hydroxy-6-hydrothymine adduct is reversible and the relative abundance of the thymine and 5-hydroxy-6-hydrothymine adducts is dependent on the pH of the spray solution. High resolution experiments using Fourier transform ion cyclotron resonance mass spectrometry confirms the presence of the thymine and hydrated thymine adducts. The high resolution nature of these experiments also allows the detection of a 5,6-dihydrothymine adduct.

Angiotensin II↗
PubMed1998

Electrospray ionization and collision-induced dissociation time-of-flight mass spectrometry of neutral glycosphingolipids.

A series of native naturally occurring neutral glycosphingolipids has been analysed by electrospray ionization tandem mass spectrometry using a hybrid magnetic sector-TOF instrument. The collision-induced dissociation products of precursor ions were detected by an orthogonal acceleration time-of-flight mass spectrometer as the second analyser. Glycosphingolipids, with mono- to hexa-saccharide chain lengths with different ceramide constituents, were studied. The result of electrospray ionization in the positive ion mode generally showed singly charged molecular ions with Na+ as adduct, [M + Na]+. The sensitivity of the electrospray ionization was greatly enhanced by addition of NaCl, LiCl (forming [M + Li]+) or KCl (yielding [M + K]+) to the sample. A comparison between the collision-induced dissociation of precursor molecular ions of monoglycosylceramides, using Na+, Li+ and K+ as adducting species, showed that the intensity of the fragment ions and the extent of the daughter ion fragmentation of the molecular ions, are dependent on the type of adduct used. The daughter ion spectra of Li+ adduct ions showed intense sequence fragment ions, both of the saccharide chain and the ceramide moiety, and were superior to those obtained using Na+ or K+. The collision-induced dissociation spectra of the [M + Li]+ ions, of glycosphingolipids containing di- to hexasaccharides, are also presented. Proposed possible fragments, resulting from the CID of the molecular ions [M + Li]+ of monoglycosylceramides, are shown.

Animals↗
PubMed1999

Internal energy content of n-butylbenzene, bromobenzene, iodobenzene and aniline molecular ions generated by two-photon ionization at 266 nm. A photodissociation study

A technique to investigate photodissociation kinetics on a nanosecond time scale has been devised for molecular ions generated by multiphoton ionization (MPI) using mass-analyzed ion kinetic energy spectrometry. The branching ratio or rate constant has been determined for the photodissociation of the n-butylbenzene, bromobenzene, iodobenzene, and aniline molecular ions generated by MPI at 266 nm. The ion internal energies have been estimated by comparing the measured kinetic data with the previous energy dependence data. The analysis has shown that only those molecular ions generated by two-photon ionization contribute to the photodissociation signals. Around half of the available energy has been found to remain as molecular ion internal energy in the two-photon ionization process. Copyright 1999 John Wiley & Sons, Ltd.

Journal Article↗
PubMed2001

Use of atmospheric pressure ionization mass spectrometry in enantioselective liquid chromatography.

Recent advances in mass spectrometry have rendered it an attractive and versatile tool in industrial and academic research laboratories. As a part of this rapid growth, a considerable body of literature has been devoted to the application of mass spectrometry in studies involving enantioselectivity, molecular recognition, and supramolecular chemistry. In concert with separation techniques such as capillary electrophoresis and liquid chromatography, mass spectrometry allows rapid characterization of a large array of molecules in complex mixtures. A majority of these findings have been made possible by the introduction of 'soft-ionization' techniques such as electrospray ionization interface. Other techniques such as atmospheric pressure chemical ionization mass spectrometry have been widely used as a rugged interface for quantitative liquid chromatography-mass spectrometry. Herein, we present a brief overview of the above techniques accompanied with several examples of enantioselective capillary electrophoresis- and liquid chromatography-mass spectrometry in drug discovery and development. Although the emphasis of this article is on quantitative enantiomeric chromatography-mass spectrometry, we envisage that similar strategies are adaptable in qualitative studies.

Atmospheric Pressure↗
PubMed1977

Serum ionized calcium in acute pancreatitis.

Measurement of serum ionized calcium was performed daily for 7 days after admission in 8 consecutive patients with acute pancreatitis. The results support the findings of our previous study that the most common cause of the low serum calcium often found in patients with this disease is a low serum albumin; when correction of serum calcium is made for hypo-albuminanemia, most patients are found to be normocalcaemic. The occasional hypocalcaemia as shown by the 'corrected' serum calcium or by serum ionized calcium measurement is usually mild and transient, indicating that the normal homoeostatic mechanisms of the body can efficiently maintain the physiologically active fraction of the serum calcium within, or close to, the normal range. These findings explain the rarity of overt and subclinical tetany in acute pancreatitis. This study has shown that correction of serum calcium for albumin provides similar information to the direct measurement of serum ionized calcium. The value of 'apparent' hypocalcemia in assessing severity of acute pancreatitis requires reappraisal, while greater attention should be directed towards the investigation and management of hypoalbuminaemia in this disease.

Acute Disease↗
PubMed1977

Peptide sequencing: the utility of chemical ionization mass spectrometry.

Chemical ionization mass spectrometry is used at low resolution to determine the sequences of permethylated acetyl peptides. The method has been tested with 45 peptides, between 2 and 5 residues long, including examples of all of the common amino acids except cysteine and N-terminal asparagine. The isobutane chemical ionization spectra contain three principal types of N-terminal sequence ion and one type of C-terminal sequence ion. The redundant information available from these four types of sequence ion increase the reliability of the sequence determination. In prospect, isobutane chemical ionization mass spectrometry seems to be a useful technique for peptide sequence determination, and may have advantages in some cases.

Amino Acid Sequence↗
PubMed1982

Determination of peptidoaminobenzophenone (2-o-chlorobenzoyl-4-chloro-N-methyl-N'-glycylglycinanilide) and its metabolites in human plasma by glass capillary gas chromatography negative ion chemical ionization mass spectrometry--1.

A highly sensitive and selective glass capillary gas chromatographic negative ion chemical ionization mass spectrometric assay was developed to measure peptidoaminobenzophenone(2-o-chlorobenzoyl-4-chloro-N-methyl-N'-glycylglycinanilide) and its metabolites; chlorodiazepam, chlorodesmethyldiazepam and lorazepam in human plasma. As peptidoaminobenzophenone underwent pyrolysis during gas chromatography, it was converted to a thermally stable aminoquinolone. Internal standards for these compounds were the respective deuterium labelled compounds. Calibration curves were prepared for the range of 1-100 ng ml-1. Interference by endogenous substances was negligible in the isobutane negative ion chemical ionization mode in contrast to the electron impact or positive ion chemical ionization mode. This method was used to determine the plasma levels in humans following oral administration of two 5 mg doses.

Anti-Anxiety Agents↗
PubMed1983

Quantitative measurement of delta 9-tetrahydrocannabinol and two major metabolites in physiological specimens using capillary column gas chromatography negative ion chemical ionization mass spectrometry.

delta 9-Tetrahydrocannabinol and two of its metabolites, 11-hydroxy-delta 9-tetrahydrocannabinol and 11-nor-9-carboxy-delta 9-tetrahydrocannabinol, can be measured in a single 1-ml sample of blood, plasma, or urine by a new assay which combines a relatively rapid extraction procedure with capillary column gas chromatography and negative ion chemical ionization mass spectrometry. Deuterium-labeled analogs of each cannabinoid are added to the physiological specimen as internal standards. Two extracts are obtained from each sample: a neutral fraction containing delta 9-tetrahydrocannabinol and 11-hydroxy-delta 9-tetrahydrocannabinol, and an acid fraction containing 11-nor-9-carboxy-delta 9-tetrahydrocannabinol. The neutral fraction is derivatized by treatment with trifluoroacetic anhydride; the acid fraction is first treated with BF3-methanol followed by reaction with trifluoroacetic anhydride. Under electron-capture chemical ionization conditions the derivatized delta 9-tetrahydrocannabinol and 11-nor-9-carboxy-delta 9-tetrahydrocannabinol give abundant molecular anions ideally suited for selected ion monitoring. The negative ion chemical ionization spectrum of the HO-THC-trifluoroacetate shows no molecular anion. Consequently, quantitation of the hydroxy metabolite is achieved by monitoring a fragment ion formed by loss of CF3CO2 from its molecular anion. The limits of reliable measurement are judged to be 0.1 ng ml-1 for 11-nor-9-carboxy-delta 9-tetrahydrocannabinol, 0.2 ng ml-1 for delta 9-tetrahydrocannabinol and 0.5 ng ml-1 for 11-hydroxy-delta 9-tetrahydrocannabinol. Four examples are given of the application of the assay to the analysis of specimens of medico-legal importance.

Adult↗
PubMed1986

Assessment of vitamin D sulphate in human milk using desorption chemical ionization mass spectrometry.

Vitamin D3 sulphate (SD3) identification in human milk was obtained using Desorption Chemical Ionization (DCI). The chemical ionization reagent gas used was nitrogen, molecules were ionized when the emitter was heated. SD3 was obtained from lactarium human milk and purified by high-performance liquid chromatography (HPLC). A selected ion monitoring (SIM) measurement was carried out with typical ions, m/z 366 for SD3 and m/z 384 for parent vitamin D3, the intensity ratio (I366/I384) greater than 1 being related to the presence of the sulphoconjugated form of vitamin D3 in the sample analysed. The detection of small quantities of SD3 in human milk is possible using this technique.

Chemical Phenomena↗
PubMed1986

Quantitation of myo-inositol as its hexakis(trifluoroacetyl) derivative with negative ion chemical ionization mass spectrometry.

Highly volatile hexakis(trifluoroacetyl) derivatives of myo-inositol and hexadeutero-myo-inositol have been prepared and analysed by capillary column gas chromatography/mass spectrometry. The electron impact and negative ion (methane) chemical ionization mass spectra of these compounds have been determined. Negative ion chemical ionization mass spectrometric analysis of hexakis(trifluoroacetyl)-myo-inositol achieves a sensitivity one order of magnitude greater than electron impact mass spectrometric analysis of hexakis(trimethylsilyl)-myo-inositol at appropriate selected ions. Stable isotope dilution measurement of myo-inositol versus hexadeutero-myo-inositol employing gas chromatography/negative ion chemical ionization mass spectrometry of the hexakis(trifluoroacetyl) derivatives is demonstrated, and this method is applied to the detection of inositol derived from hydrolysis of water-soluble inositol phosphates obtained from isolated pancreatic islets.

Animals↗
PubMed1987

Isotope effect in negative ion chemical ionization mass spectrometry of deuterium labelled lormetazepam.

This study identified the reason for the poor quantification of lormetazepam-TMS (1) using negative ion chemical ionization with lormetazepam-1,1,1-2H3-TMS (2) as an internal standard. Mass spectra of lormetazepam and its deuterium labelled compounds determined at various ion source temperatures (100-250 degrees C) gave almost the same behaviour for 1 and lormetazepam-3',4',5',6'-2H4-TMS (3) but a different one for 2, suggesting that the poor quantification was due to an isotope effect. This was confirmed by the findings that the ratios of ion currents of the base peaks of 1 and 3 were independent of the ion source temperature but those of 1 and 2 varied markedly with it. This phenomenon was also observed in the mass fragmentography of the molecular ion, although to a lesser degree than that of the above fragment. In both positive ion chemical ionization and electron impact ionization modes, no isotope effect arose because there was no corresponding fragment to cause the isotope effect.

Anti-Anxiety Agents↗
PubMed1987

Analysis of phospholipid molecular species in rat lung as dinitrobenzoate diglycerides by electron capture negative chemical ionization mass spectrometry.

The use of electron capture negative ion desorption chemical ionization mass spectrometry was demonstrated in the analysis of phospholipid molecular species at the 1,3-dinitrobenzoate (DNB) diglyceride derivative. Modification of phosphatidylcholine (PC) or phosphatidylethanolamine (PE) by phospholipase C treatment and acylation of the resultant diglyceride with 3,5-dinitrobenzoylchloride afforded separation of the alkylacyl, alkenylacyl, and diacyl dinitrobenzoate subclasses by thin-layer chromatography (TLC). Separation of alkylacyl DNB into individual molecular species by reverse-phase high-performance liquid chromatography (RPHPLC) was demonstrated. Electron capture desorption chemical ionization of individual molecular species (10-25 ng) from a direct probe yielded a mass spectrum characterized by an intense molecular anion. This molecular anion was the base peak of the spectrum accounting for greater than 80% of the total ionization. From this molecular anion the total carbon number and degree of unsaturation of the fatty chains could be determined. Analysis of fatty acid content of the molecular species allowed unequivocal assignment of structure for the alkyl ether phospholipids. Using selected ion monitoring as little as 0.5 pmol of these species could be detected with a signal-to-noise ratio greater than or equal to 3. This technique was useful in the analysis of low picomolar amounts of molecular species of ether phospholipids in the rat lung. Given an appropriate internal standard, analysis of dynamic changes in turnover, metabolism and precursor product relationships could be undertaken.

Animals↗
PubMed1988

Direct chemical ionization-pattern recognition: characterization of bacteria and body fluid profiling.

Direct chemical ionization is ideally suited for profiling purposes because it is a relatively soft ionization method, easy to operate, reproducible and with a high sample throughput. Moreover, for non-volatile matrices the method combines pyrolysis with an optimal pyrolysate transfer to the ionization region enabling the detection of high molecular weight compounds. Application of the technique to urine analysis of women with a premenstrual syndrome and characterization of Salmonella bacteria illustrates its usefulness. Optimal information extraction from the profiles is, because of their complex nature, only possible using pattern recognition techniques. A new approach based on the data analysis of trend spectra is discussed.

Bacteria↗
PubMed1988

Mass spectrometric investigation of dissociative ionization of toxic gases by electrons at 20-1000 eV.

Measurements of the dissociative ionization cross-sections of CO, CO2, NO and N2O molecules for electrons from 20 up to 1000 eV were performed. Total collection of ions was achieved by using a specially constructed cycloidal mass spectrometer, an ion source without slit and a collector with large area. In that open ion source the effusion molecular beam formed by a capillary was crossed by the electron beam. Owing to such parameters of the mass spectrometer the mass discrimination effects were reduced. At the ionization of CO molecules, the ions CO+, C+, O+ and CO2+ were registered; at CO2, the ions CO2+, CO+, O+, C+ and CO2(2)+; at NO, the ions NO+, N+, O+ and NO2+; at N2O, the ions N2O+, NO+, N2+, O+, (N+,N2(2)+) and N2O2+. The relative values of the partial cross-sections were normalized to the absolute total ionization cross-sections obtained by Rapp and Englander-Golden.

Carbon Dioxide↗
PubMed1990

Characterization of the reaction products of deoxyguanosine with the anticancer agent BFNU and BFNU-1,1,1',1'-d4 in different buffers by high-performance liquid chromatography/atmospheric pressure ionization tandem mass spectrometry.

The products of the reaction of the anticancer agent 1,3-bis(2-fluoroethyl)-1-nitrosourea (BFNU) and BFNU-1,1,1',1'-d4 with the DNA base deoxyguanosine were characterized by applying high-performance liquid chromatography (HPLC)/tandem mass spectrometry. The total effluent from the HPLC column was introduced into the atmospheric pressure ionization (API) source of a triple-quadrupole mass spectrometer via a heated nebulizer. The gasified mixture produced from the heated nebulizer was exposed to corona discharge ionization which led to generation of gas-phase chemical ionization type of ions. The LC/API mass spectrometry produced ions and the tandem mass spectra allowed unambiguous identification, and assignment of positions of the deuterium atoms, in the products of the reaction under a variety of experimental conditions. The identification and characterization of a variety of 7-(2'-haloethyl)guanine derivatives among the reaction products provide confirmation of a proposed mechanism for the action of BFNU on DNA bases.

Antineoplastic Agents↗
PubMed1992

Optimization of short-column gas chromatography/electron ionization mass spectrometry conditions for the determination of underivatized anabolic steroids.

A gas chromatographic/mass spectrometric method based on the use of short capillary gas chromatograph columns (3-5 m) and electron ionization mass spectrometry has been optimized and evaluated for the determination of underivatized anabolic steroids. The short-column gas chromatographic/mass spectrometric method was shown to result in short analysis times and to require minimal sample preparation, but suffered from some loss in sensitivity and chromatographic resolution compared with conventional gas chromatographic/mass spectrometric techniques for derivatized steroids. Therefore, short-column gas chromatographic conditions were optimized to maximize the sample transfer efficiency (sensitivity) from the gas chromatograph into the ion source of the mass spectrometer, while maintaining chromatographic integrity and minimizing thermal decomposition. Mass spectrometric conditions were optimized to maximize ionization efficiency with respect to the intensity of the molecular ion and degree of fragmentation such that positive identification of each steroid could be made based on the resulting mass spectra. Under optimized conditions, we have shown that underivatized anabolic steroids spiked into urine samples can be determined at low-nanogram levels using short-column chromatography/full-scan electron ionization mass spectrometry.

Anabolic Agents↗