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R G Cooks

Publications and source records attributed to R G Cooks.

47 records · Page 3Linked to original sources
PubMed1983

Mass spectrometry: analytical capabilities and potentials.

The mass range of mass spectrometers has been extended by almost an order of magnitude in the past decade, ionization procedures have been introduced which allow ionic, nonvolatile compounds to be examined, and new capabilities have been achieved through the successful integration of separation and analysis techniques. In combination with other techniques, mass spectrometry has been used in biological and environmental research to characterize constituents of mixtures, including those present in trace amounts; in metabolic profiling, where high throughput and large dynamic range are important; and in protein structure determinations. Measurements of stable isotope abundances by mass spectrometry have been used in enzymology, studies of photosynthesis, and carbon dating. Outside the area of chemical analysis, mass spectrometry has been used to study gas-phase acidities and basicities and to study organic reaction mechanisms in the gas phase. Trends in mass spectrometry include multidimensional experiments, use of ionization methods, direct analysis without extensive sample preparation, and the development of advanced instrumentation including an ion trap and an inductively coupled plasma mass spectrometer. It is likely that mass spectrometry will come to be much more widely used and that data will increasingly be other than conventional mass spectra.

Fourier Analysis↗
PubMedDate not supplied

Membrane introduction mass spectrometry: trends and applications.

Recent advances in membrane introduction mass spectrometry (MIMS) are reviewed. On-line monitoring is treated by focusing on critical variables, including the nature and dimensions of the membrane, and the analyte vapor pressure, diffusivity, and solubility in the membrane barrier. Sample introduction by MIMS is applied in (i) on-line monitoring of chemical and biological reactors, (ii) analysis of volatile organic compounds in environmental matrices, including air, water and soil, and (iii) in more fundamental studies, such as measurements of thermochemical properties, reaction mechanisms, and kinetics. New semipermeable membranes are discussed, including those consisting of thin polymers, low vapor pressure liquids, and zeolites. These membranes have been used to monitor polar compounds, selectively differentiate compounds through affinity-binding, and provide isomer differentiation based on molecular size. Measurements at high spatial resolution, for example, using silicone-capped hypodermic needle inlets, are also covered, as is electrically driven sampling through microporous membranes. Other variations on the basic MIMS experiment include analyte preconcentration through cryotrapping (CT-MIMS) or trapping in the membrane (trap-and-release), as well as differential thermal release methods and reverse phase (i.e., organic solvent) MIMS. Method limitations center on semivolatile compounds and complex mixture analysis, and novel solutions are discussed. Semivolatile compounds have been monitored with thermally assisted desorption, ultrathin membranes and derivatization techniques. Taking advantage of the differences in time of membrane permeation, mixtures of structurally similar compounds have been differentiated by using sample modulation techniques and by temperature-programmed desorption from a membrane interface. Selective ionization techniques that increase instrument sensitivity towards polar compounds are also described, and comparisons are made with other direct sampling (nonchromatographic) methods that are useful in mixture analysis.

Bioreactors↗
PubMedDate not supplied

Mass-analyzed ion kinetic energy (MIKE) spectrometry and the direct analysis of coca.

The technique of mass-analyzed ion kinetic energy (MIKE) spectrometry is briefly reviewed. The direct analysis, without need of prior extraction or chromatographic purification, of cocaine and cinnamoylcocaine in coca plant tissues has been accomplished with this new technique. Detection limits of below 1 ng, with a quantitative accuracy of +/- 30% at the nanogram level, have been demonstrated.

Alkaloids↗
PubMedDate not supplied

Identification of new cactus alkaloids in Backebergia militaris by tandem mass spectrometry.

Tandem mass spectrometry, applied to simple extracts of Backebergia militaris, indicated the presence of a number of new alkaloids, including fully aromatic oxygenated isoquinolines, their di- and tetra-hydro analogs, and beta-phenethylamines. These conclusions were supported by separation using radial tlc and comparison with authentic compounds. Traces of seven alkaloids new to this cactus species were identified; four (3,4,8,11) were known previously from other cacti. Three novel cactus alkaloids were identified and confirmed by synthesis as 7,8-dimethoxy-3,4-dihydroisoquinoline (12, dehydrolemaireocereine), 6,7-dimethoxyisoquinoline (13, backebergine), and 7,8-dimethoxyisoquinoline (14, isobackebergine). The last two compounds are the first simple, fully aromatic, isoquinoline alkaloids to be reported from the Cactaceae. The sensitivity of this approach to new alkaloid discovery is emphasized; the entire project consumed only 10 g of dried plant material.

Alkaloids↗
PubMedDate not supplied

Antineoplastic agents from higher plants: application of tandem mass spectrometry to xanthones from Psorospermum febrifugum.

Psorospermum febrifugum was examined using tandem ms for the presence of 3',4'-deoxypsorospermin-4'-chloro-3'-ol and psorospermin. Collision-induced dissociation at both high and low energy is used to bring about fragmentation. Daughter spectra were interpreted to reveal characteristic fragmentations for both compounds. Examination of the authentic compounds, various extracts of the plant root, and the plant root material itself established that psorospermin occurs naturally in the plant. The data also suggest the presence of the chlorohydrin in the root, as well as establishing its presence in the root extracts. The detection of neutral compounds in complex mixtures by tandem ms is facilitated if comparisons can be made between spectra resulting from different methods of ionization and excitation.

Antineoplastic Agents, Phytogenic↗
PubMedDate not supplied

Cactus alkaloids. XXXVI. Mescaline and related compounds from Trichocereus peruvianus.

Agurell has previously detected (tlc, glc-ms) tyramine, 3-methoxytyramine, and two unknown alkaloids in the Peruvian cactus, Trichocereus peruvianus Br. and R. The presence of mescaline in other similar Trichocereus species prompted us to reinvestigate this species, which is commercially available in the United States. The nonphenolic alkaloid extracts yielded an abundance of crystalline mescaline hydrochloride (0.82% yield) and a trace of 3,4-dimethoxyphenethylamine (tlc-ms). Crystalline tyramine hydrochloride, 3-methoxytyramine hydrochloride, and 3,5 dimethoxy-4-hydroxphenethylamine hydrochloride were isolated from the phenolic alkaloid extracts; the last compound has not been previously crystallized from nature, although it is the immediate biosynthetic precursor of mescaline. Crystalline 2-chloromescaline hydrochloride was isolated drom the nonphenolic extracts; but, as determined by mass-analyzed ion kinetic energy spectrometry, this new compound is an extraction artifact. Both 2-chloromescaline and 2.6-dichloromescaline hydrochlorides were prepared synthetically from mescaline. This cactus species has a mescaline content equal or superior to peyote and should be legally controlled as an item of drug abuse.

Chemical Phenomena↗