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At least 109 records · Page 6Linked to original sources
PubMed1999

Ion-pair liquid chromatography--atmospheric pressure ionization mass spectrometry for the determination of quaternary ammonium herbicides.

High-performance liquid chromatography coupled with atmospheric pressure ionization mass spectrometry (electrospray and atmospheric pressure chemical ionization) has been used to characterize some quaternary ammonium herbicides (quats). The separation of these compounds was carried out using ion-pair chromatography with heptafluorobutyric acid (15 mM, pH 3.3) and acetonitrile gradient elution for successful coupling to mass spectrometry. Detection limits down to 0.1-4 micrograms l-1 were obtained for spiked tap water following a preconcentration step. Good reproducibilities (day-to-day and run-to-run) were also obtained.

Atmospheric Pressure↗
PubMed2002

Immobilized artificial membrane chromatography coupled with atmospheric pressure ionization mass spectrometry.

Liquid chromatographic separations on monolayers of cell membrane phospholipids covalently immobilized to silica particles at high molecular density is used for mimicking solute partitioning into biological membranes that generally correlates with membrane transport. This technique called immobilized artificial membrane chromatography usually employs ultraviolet (UV) detection where a single compound is analyzed in a chromatographic run limiting thereby its throughput for drug discovery applications. For coupling with atmospheric pressure ionization mass spectrometry, the phosphate-buffered saline mobile phase was replaced with one that used ammonium acetate as a volatile buffer. While atmospheric pressure chemical ionization accommodated a purely aqueous effluent, interfacing with electrospray ionization required effluent splitting and the addition of an organic modifier (5%, v/v, acetonitrile). Neuropeptide FF antagonists as early-phase drug candidates were used for the comparative evaluation of the methods. Whereas electrospray ionization produced essentially no fragment ions, several compounds involved in our study yielded low-abundance molecular ions with atmospheric pressure chemical ionization. The use of mass spectrometry yielded data that correlated well with those obtained by the method employing UV detection. Both atmospheric pressure ionization methods permitted the simultaneous determination of the k'(IAM), capacity factors and, therefore, an increased-throughput ranking of potential new leads emerged from the drug discovery process based on affinity to artificial membranes.

Atmospheric Pressure↗
PubMed1980

The independent effects of atmospheric pressure and oxygen partial pressure on gas exchange of the chicken embryo.

CO2 production and air cell PCO2 were continuously measured during late development in the chicken egg while acutely exposed from one to three hours to various O2 concentrations ranging from 11 to 39%. A small but significant increase in metabolism, ca. 8%, was found when O2 concentration was above normal values, while a reduction to 70% was observed when O2 concentrations were below normal, and fell to 50% when maintained for three hours. These values were also compared with metabolic rates reported by Lokhorst and Romijn (1965, 1967)) who incubated eggs continuously at reduced O2 concentrations as well as under reduced barometric pressure, and showed that at the same ambient PO2 the metabolism was significantly higher in the eggs at reduced barometric pressure. We attribute this difference to the increased diffusion coefficient of O2 which is inversely related to the barometric pressure. It illustrates that the ambient partial pressure of O2 and ambient atmospheric pressure exert an independent effect upon gas exchange of the avian embryo.

Animals↗
PubMed2005

Structural characterization of phosphatidylcholines by atmospheric pressure photoionization mass spectrometry.

The potential of atmospheric pressure photoionization was investigated for the structural analysis of phosphatidylcholine lipids (PCs). [M+H]+ ions of high abundance were obtained, along with several fragment ions. Three of these dissociation products corresponded to quite unusual fragmentation pathways but allowed the determination of both the nature and the position on the glycerol backbone (sn-1 or sn-2) of the fatty acyl chains. The loss of a methyl group from the choline head was also observed. These results suggest a complex ionization mechanism in APPI. However, this method proved to be very powerful for the rapid structural analysis of PC species without using MS/MS experiments.

Atmospheric Pressure↗
PubMed2004

Study of peptide-sugar non-covalent complexes by infrared atmospheric pressure matrix-assisted laser desorption/ionization.

Infrared atmospheric pressure matrix-assisted laser desorption/ionization quadrupole ion trap mass spectrometry was applied to the study of siglec binding to oligosaccharide ligands. Peptides were designed to mimic the binding sites of three members of the siglec family: sialoadhesin, MAG and CD22. These peptides were tested for their ability to complex with their carbohydrate ligands 3'-sialyllactose (3'SL) and 6'-sialyllactose (6'SL). All peptides demonstrated the ability to bind to the carbohydrates, with the peptide representing sialoadhesin maintaining its binding specificity for 3'SL in preference to 6'SL. This technique can be used to study other protein-sugar interactions and can be expanded to create high-throughput screening techniques.

Atmospheric Pressure↗
PubMed1991

[Influence of atmospheric pressure fluctuation on condition of patients with cor pulmonale].

Based on investigation of 632 patients with cor pulmonale, we found that there were a close corresponding relationship of attack, exacerbation and death of patients to negative variation of daily atmospheric pressure. It was more obvious that the persistent and significant decrease in atmospheric pressure could influence the patient situation. The disease attacks usually appeared behind in negative variation of pressure changes, however, the death did before them. The mechanism of influences of atmospheric pressure changes on situation of patients with cor pulmonale were discussed preliminarily. The authors point out that the disease condition might be predicted by forecast and should take preventive measures to avoid it in advance.

Atmospheric Pressure↗
PubMed2003

Identification of diastereomeric chlorophyll allomers by atmospheric pressure chemical ionisation liquid chromatography/tandem mass spectrometry.

Atmospheric pressure chemical ionisation liquid chromatography/mass spectrometry (APCI-LC/MS) has been used for identification of the epimers of hydroxy, methoxy and methoxylactone allomers of chlorophyll a (13(2)-HO-chl a, 13(2)-MeO-chl a and 15(1)-MeO-lact-chl a), the hydroxy allomer of bacteriochlorophyll a (13(2)-HO-bchl a) and the hydroxy and methoxylactone allomers of bacterioviridin a (13(2)-HO-bvir a and 15(1)-MeO-lact-bvir a). The APCI mass spectra show that facile fragmentations involve the methoxyl or hydroxyl groups at the C-13(2) or C-15(1) chiral centres. Losses involving the C-13(2) or C-15(1) hydroxyl or methoxyl groups occur more easily from the S-epimer than from the R-epimer due to the greater relief of the steric strain associated with interaction with the bulky C-17 substituent. The differences in mass spectrometric fragmentation can be used as a diagnostic tool for the assignment of the stereochemical configuration at the C-13(2) or C-15(1) chiral centres.

Atmospheric Pressure↗
PubMed2006

Gas chromatography-microchip atmospheric pressure chemical ionization-mass spectrometry.

An atmospheric pressure chemical ionization (APCI) microchip is presented for combining a gas chromatograph (GC) to a mass spectrometer (MS). The chip includes capillary insertion channel, stopper, vaporizer channel, nozzle and nebulizer gas inlet fabricated on the silicon wafer, and a platinum heater sputtered on a glass wafer. These two wafers are joined by anodic bonding creating a two-dimensional version of an APCI microchip. The sample from GC is directed via heated transfer line capillary to the vaporizer channel of the APCI chip. The etched nozzle forms narrow sample plume, which is ionized by an external corona discharge needle, and the ions are analyzed by a mass spectrometer. The GC-microchip APCI-MS combination provides an efficient method for qualitative and quantitative analysis. The spectra produced by microchip APCI show intensive protonated molecule and some fragmentation products as in classical chemical ionization for structure elucidation. In quantitative analysis the GC-microchip APCI-MS showed good linearity (r(2) = 0.9989) and repeatability (relative standard deviation 4.4%). The limits of detection with signal-to-noise ratio of three were between 0.5 and 2 micromol/L with MS mode using selected ion monitoring and 0.05 micromol/L with MS/MS using multiple reaction monitoring.

Anisoles↗
PubMedDate not supplied

[The characteristics of the modulation of afferent reactions by adrenergic and cholinergic preparations and by the electrostimulation of the skin under conditions of changing atmospheric pressure].

The authors studied the organism's afferent reactions in changing conditions of atmospheric pressure in electrostimulation of skin zones during application of adren- and cholinergic agents. All of the studied adren- and cholinolytic agents facilitated the inhibition of afferent reactions, in contrast to mediation intensifying agents. The results of the experiments suggest that the nociceptive thresholds at atmospheric pressure of 550 mm Hg reduce, which may be linked with intensification of the catecholamine reactions of the organism of untrained animals. This is confirmed by the results of experiments with inderal injection, in which the effect of inhibition of the induced afferentation is most marked at pressure of 550 and 360 mm Hg. Besides, the analgesic activity of benactyzine diminished under similar conditions. Inderal and benactyzine potentiate the analgesic effect of percutaneous electroneurostimulation.

Afferent Pathways↗
PubMed2006

[Spectroscopic diagnostics of DC argon plasma at atmospheric pressure].

The optical emission spectra of DC argon plasma at atmospheric pressure were measured inside and outside the arc chamber. The electron temperature was determined from the Boltzmann plot, and the electron density was derived from Stark broadening of Ar I lines. The criteria for the existence of local thermodynamic equilibrium (LTE)in the plasma was discussed. The results indicate that the DC argon plasma at atmospheric pressure under our experimental conditions is in LTE.

English Abstract↗
PubMed1969

Resistance of the protozoan Colpoda maupasi to Martian conditions of atmospheric pressure and low partial pressure of oxygen.

Among the most important factors limiting the active life of animal organisms in Martian conditions are low atmospheric pressure and insignificant amounts of oxygen in the atmosphere (no more than 0.15% of the Earth's atmosphere). The experiments with aerobic protozoon C. maupasi have shown that in conditions of hermetically sealed chambers, for instance in 2.5 liter anaerostats, the protozoon can survive for a long time and reproduce in an atmosphere of air or nitrogen containing 1 or 0.0005% oxygen at a pressure from 15 mm Hg and higher. At the atmospheric pressure 10 mm Hg we observed a considerable decrease in the survival percentage and no reproduction. The exposure to 5 mm Hg resulted in a 100 per cent mortality of the protozoon. In a specially-constructed chamber "Photostat", in which current atmosphere pressure were automatically maintained during an experiment of many days, the reaction of the infusoria was somewhat different: they reproduced and existed not only at the pressure of 10-15 mm Hg, but also at 5 mm Hg, in an atmosphere of both air and nitrogen containing from 1 to 0.0005% O2. This indicates not only low-oxygen consumption of unicellular animals but also the capability of cells to extract some traces of this gas from the atmosphere. Low pressure and some traces of oxygen in the Martian atmosphere are not an impediment for the existence of some of the Earth's animals, such as the protozoon C. maupasi for example.

Anaerobiosis↗
PubMed2004

Atmospheric pressure photoionization. II. Dual source ionization.

In this paper we describe results based on the combination of atmospheric pressure photoionization (APPI) with atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI). The main purpose of combining more than one ionizer is to extend the range of compounds that can be simultaneously analyzed. Three modes of operation are presented; use of either ionizer, simultaneous use of two ionizers, and rapid switching between ionizers during a single chromatographic run. The dual ionizer configurations only minimally affect the performance of either ionizer relative to the standard single-ionizer sources. However, it is observed that the operation of both ionizers together does not typically give the sum signal from either source operating alone. For APCI/APPI the signal can range from less than that of either source alone to the sum of the two individual sources. For ESI/APPI, we observed large suppressions of the ESI multiply-charged signal of proteins when the APPI source was on. These behaviors are presumed to be due to the interaction of the initially formed ions by both sources and attests to the importance of ion-molecule reactions that occur during and after the primary ionization events. We give examples of compounds that are preferentially ionized by either APPI, APCI or ESI and present thermochemical arguments based on molecular structure and functionality to explain this behavior. The dual source is also shown to be able to operate in negative ion mode opening up the potential to conduct wide ranging chemical analyses.

Air Pressure↗
PubMed2006

Determination of gambogic acid in human plasma by liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry.

A high-performance liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (HPLC-APCI-MS) method was established for the determination of gambogic acid (GA) in human plasma using ursolic acid as the internal standard (I.S.). Plasma samples were extracted with ethyl acetate and separated on a Hanbon Lichrospher 5-C18 column with a mobile phase of acetonitrile-tetrahydrofuran-water (70:23:7, v/v). Gambogic acid was determined by using atmospheric pressure chemical ionization (APCI) in a single quadrupole mass spectrometer. HPLC-APCI-MS was performed in the selected ion monitoring (SIM) mode using target ions at [M-H](-)m/z 627.4 for gambogic acid and [M-H](-)m/z 455.4 for the I.S. Calibration curve was linear over the range of 3.108-4144 microg/L. The lower limit of quantification was 3.108 microg/L. The intra- and inter-run precisions were less than 12.3 and 14.1%, respectively. The method has been successfully applied to study the pharmacokinetics of gambogic acid in patients with malignant tumour.

Atmospheric Pressure↗
PubMed2002

Atmospheric pressure ionization LC-MS-MS determination of urushiol congeners.

This paper describes atmospheric pressure ionization (API) LC-MS-MS determination of urushiols, 3-n-alkenyl- and -alkyl-substituted catechols responsible for poison oak dermatitis. Urushiol was isolated from Western poison oak according to the method of Elsohly et al. (1) (J. Nat. Prod. 1982, 45, 532-538)-the purified preparation contained C(17)- and C(15)-substituted urushiols with zero, one, two, and three double bonds as determined from GC-MS analysis of trimethylsilyl derivatives. Urushiol mixtures were separated on a C(18) reversed phase HPLC column with a methanol-water gradient with urushiols eluting in 100% methanol. Atmospheric pressure chemical ionization (APCI) produced primarily [M - H](-) and MH(+) molecule ions. Electrospray ionization (ESI) yielded [M - H](-) and adduct ions including [M + Cl](-). Daughter ions of [M - H](-) included quinoid radical anions ([M - H - H(2)](-) and m/z 122(-)) and a benzofuran phenate (m/z 135(-)). A suite of hydrocarbon fragments were produced by collision-induced dissociation of MH(+) directly or via an intermediate [MH - H(2)O](+) daughter ion. Six urushiol congeners, one not previously reported in poison oak, were determined by negative ion API-LC-MS-MS with detection limits of approximately 8 pg/microL (ESI) and approximately 800 pg/microL (APCI). API-LC-MS-MS was used to determine urushiol in surface wipes, air samples, and plant materials.

Atmospheric Pressure↗
PubMed2002

Atmospheric pressure laser desorption/chemical ionization mass spectrometry: a new ionization method based on existing themes.

We have designed and constructed an atmospheric pressure laser desorption/chemical ionization (AP-LD/CI) source that utilizes a laser pulse to desorb intact neutral molecules, followed by chemical ionization via reagent ions produced by a corona discharge. This source employs a heated capillary atmospheric pressure inlet coupled to a quadrupole ion trap mass spectrometer and allows sampling under normal ambient air conditions. Preliminary results demonstrate that this technique provides approximately 150-fold increase in analyte ions compared to the ion population generated by atmospheric pressure infrared matrix-assisted laser desorption/ionization (AP-IR-MALDI).

Air Pressure↗
PubMedDate not supplied

Effect of pressurized atmosphere on void size and quantity in dental stone and fine-grained phosphate-bonded investment.

This study investigated the effect of pressurized atmosphere on the size and number of voids in dental stones and investments. Control specimens of casts and invested patterns were bench set. Experimental specimens of casts and invested patterns were allowed to set under pressure. The specimens were then sectioned and voids counted and measured to establish a mean. Increased atmospheric pressure reduced the size and number of voids. This method produces improved cast surfaces and fewer, smaller voids in investments. Technicians are continuously searching for ways to improve the quality of their products. One method is placing dental casts and dental investments under increased atmospheric pressure while setting. Several pressure vessels are available for this purpose.

Calcium Sulfate↗