Accurate mass measurements of positive ions in the desorption chemical ionization mode

Desorption chemical ionization mass spectrometry employing ammonia as the reagent gas has been extensively used to obtain molecular mass and structural information on a wide variety of compounds. Mass-deficient reference standards normally used for calibration purposes in mass spectrometry do not provide adequate mass spectra under ammonia chemical ionization conditions. In order to overcome this problem a mixture of ammonia and methane as reagent gases was employed. In high-resolution accurate mass measurement experiments, this gas mixture allows the simultaneous detection of mass spectra of perfluorokerosene adequate for calibration purposes and spectra containing molecular mass information of the analyte. A needle valve system was used to control the composition of the gas mixture introduced into the ion source. For positive-ion accurate mass measurements of higher masses (up to m/z = 2300), Fomblin 18/8 oil was successfully used as a reference standard under ammonia, methane and isobutane desorption chemical ionization conditions.     

Arsenic biomethylation by the microorganism apiotrichum humicola in the presence of l-methionine-methyl-d3

The microorganism Apiotrichum humicola (previously known as Candida humicola) grown in the presence of either arsenate, arsenite, methylarsonic acid or dimethylarsinic acid, produces arsenic-containing metabolites in the growth medium. When L-methionine-methyl-d₃ is added to the cultures, the CD₃ label is incorporated intact into the metabolites to a considerable extent to form deuterated dimethylarsenic and trimethyl-arsenic species, indicating that S-adenosylmethionine, or some related sulphonium compound, is involved in the biological methylation. Conclusive evidence of CD₃ incorporation in the arsenicals found in the growth medium was provided by using a specially developed hydride generation-gas chromatography-mass spectrometry system (HG–GC–MS).     

New Triterpenes from the Bark of Western White Pine (Pinus monticola DOUGL.)

Eleven new triterpenes with the lanostene-type skeleton were isolated from the benzene extract of western white pine bark. Their structures were determined mainly on the basis of physical and spectral data.     

Detection of lyso-platelet-activating factor by high-performance liquid chromatography after derivatisation with fluorescent fatty acids

Lyso-platelet-activating factor (lyso-PAF) was derivatised with 9-anthracenepropionic acid in the presence of dicyclohexylcarbodiimide, p-toluenesulfonic acid and 4-dimethylaminopyridine. The reaction yield exceeded 90% when the fatty acid was present in double molar amounts versus lyso-PAF. The procedure was equally effective in the derivatisation of other lysophospholipids. The derivatized phospholipids are detected by ultraviolet absorption (lambda = 253 nm) or fluorescence detection (using excitation at 254 nm and emission at 450 nm). The technique was applied successfully to the detection of lyso-PAF in complement activated rabbit plasma.     

Isolation and synthesis of glutamine and glutarimide derivatives fromCroton humilis

Extract ofCroton humilis L. were shown to contain N - [N - (2 - methylpropanoyl) -l - glutaminoyl] - 2 - phenylethylamine, N - [N - 2R - methylbutanoyl) -l - glutaminoyl] - 2 - phenylethylamine, 2 - [N- (2 - methylpropanoyl)] - N - phenylethylglutarimide and 2 - [N- (2R - methylbutanoyl)] - N - phenylethylglutarimide. Structural proof was based on acid degradation, spectral studies as well as the synthesis of N - [N- (2- methylpropanoyl) -l - glutaminoyl] - 2 - phenylethylamine and 2 - [N - (2 - methylpropanoyl] - N - phenylethylglutarimide.     

Synthesis of Novel Receptors From 7-Deoxycholic Acid and Studies on Their Cation Binding Properties

The synthesis and cation binding properties of chiral crown ethers derived from 7-deoxycholic acid along with their application in asymmetric Michael reaction are described.     

Ion-molecule reactions of dimethyl ether cations with polycyclic aromatic hydrocarbons in a quadrupole ion trap mass spectrometer

The reaction chemistry between dimethyl ether (DME) cations and polycyclic aromatic hydrocarbons (PAHs) was elucidated by isolating three different types of DME ions using a quadrupole ion trap and reacting them individually with neutral PAH molecules eluting from a gas chromatographic column. The results obtained show that the CH(2)OCH(3)(+) ion (m/z 45) reacts via adduct formation followed by elimination of CH(3)OH, the (CH(3))(2)OH(+) (m/z 47) ion serves as proton donor and the (CH(3))(3)O(+) ion (m/z 61) does not yield any reaction products. Copyright 1999 John Wiley & Sons, Ltd.     

The quantitation of butyltin and cyclohexyltin compounds in the marine environment of British Columbia

A HPLC/GF AA procedure based on the use of C-18 columns is described for the quantitation of butyltin species in marine samples. When a mass spectrometer was used as detector (HPLC MS), evidence was obtained for the presence of other tin compounds in the samples. Extracts of samples were treated with CH₃MgBr and examined by using GC MS; the presence of Bu_nSnMe_4?n (n = 3–1, Bu = butyl) and Cy_nSnMe_4?n (n = 3,2, Cy = cyclohexyl) was confirmed in the derivatized seawater, bivalve flesh, and bivalve shell samples. Quantitative data are given for butyl- and cyclohexyl-tin species in seawater and the surface microlayer, and oyster flesh.