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Results for “ATMOSPHERIC PRESSURE”

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At least 379 records · Page 21Linked to original sources

PubMed2002

Comparative analysis of different plant oils by high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.

Different vegetable oil samples (almond, avocado, corngerm, grapeseed, linseed, olive, peanut, pumpkin seed, soybean, sunflower, walnut, wheatgerm) were analyzed using high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry. A gradient elution technique was applied using acetone-acetonitrile eluent systems on an ODS column (Purospher, RP-18e, 125 x 4 mm, 5 microm). Identification of triacylglycerols (TAGs) was based on the pseudomolecular ion [M+1]+ and the diacylglycerol fragments. The positional isomers of triacylglycerol were identified from the relative intensities of the [M-RCO2]+ fragments. Linear discriminant analysis (LDA) as a common multivariate mathematical-statistical calculation was successfully used to distinguish the oils based on their TAG composition. LDA showed that 97.6% of the samples were classified correctly.

Atmospheric Pressure↗

PubMed2005

Experimental method for determining the damping parameter of spectral lines emitted by a microwave plasma at atmospheric pressure.

In this work, a simple method for experimentally obtaining the value of the damping parameter or a-parameter of the spectral lines emitted by an argon plasma generated at atmospheric pressure is presented. The value of this coefficient indicates the proportion existing between the Lorentzian and Doppler components of the total line profile, which can be approximated to a Voigt function for our experimental conditions. The a-parameter values found were within the value interval recorded in the literature. The results obtained showed that the damping coefficient of the lines next to the fundamental level remains practically constant along the plasma column, whereas for the spectral lines involving high-lying levels, the a-parameter is sensitive to the changes in the electron density in the plasma. In this work it is also proved that the self-absorption phenomenon induces errors in the calculation of a, due to an increase in the broadening of the line profile produced by this phenomenon.

Algorithms↗

PubMed1996

Simple and rapid quantitative assay of 13C-labelled urea in human serum using liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.

A simple and rapid quantitative method for 13C-labelled urea ([13C]urea) in human serum was developed by using high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (HPLC-APCI-MS). This method is used to establish and normalize the [13C]urea breath test, which is considered as an effective diagnostic method for Helicobacter pylori infection. HPLC-APCI-MS, involving a simple pretreatment process such as diluting serum with water, was shown to be able to discriminate the extrinsic [13C]urea from intrinsic urea present at high concentration in serum. In addition, a 13C nuclear magnetic resonance spectroscopic quantitative method for [13C]urea in human urine is also described. The precision and accuracy of measured concentrations in these two methods were found to be within the acceptable limit. An application of these methods to investigate the pharmacokinetic profile of orally administered [13C]urea in human serum and urine is also presented.

Adult↗

PubMed2006

Atmospheric pressure desorption/ionization on silicon ion trap mass spectrometry applied to the quantitation of midazolam in rat plasma and determination of midazolam 1'-hydroxylation kinetics in human liver microsomes.

The application of atmospheric pressure desorption/ionization on silicon (AP-DIOS) coupled with ion trap mass spectrometry (ITMS) was investigated for the quantification of midazolam in rat plasma, and determination of midazolam 1'-hydroxylation kinetics in pooled human liver microsomes. Results indicate good sensitivity with absolute detection limits for midazolam in rat plasma of approximately 300 femtograms. A linear dynamic range from approximately 10-5000 ng/mL was obtained in rat plasma with analysis times of 1 min per sample. Kinetic constants for midazolam 1'-hydroxylation in human liver microsomes yielded an apparent Km of 10.0 microM and Vmax of 6.4 nmol/min/mg. Studies investigating the inhibition of 1'-hydroxymidazolam formation by the cytochrome P450 3A4 model inhibitor ketoconazole yielded an IC50 of 0.03 microM. Quantitative precision for replicate analysis of rat plasma and human liver microsomal samples was variable with relative standard deviation (RSD) values ranging from a low of approximately 3% to over 50%, with the highest variability observed in data from human liver microsomal incubations. While preliminary studies investigating the application of AP-DIOS-ITMS suggested feasibility of this technique to typical pharmacokinetic applications, further work is required to understand the underlying causes for the high variability observed in these investigations.

Animals↗

PubMed1995

Multiresidue determination of quinolone antibiotics using liquid chromatography coupled to atmospheric-pressure chemical ionization mass spectrometry and tandem mass spectrometry.

Liquid chromatography coupled to atmospheric-pressure chemical ionization mass spectrometry and tandem mass spectrometry (MS/MS) methods for the determination and quantification of four quinolone antibiotics were adapted from a published procedure for liquid-liquid extraction from catfish muscle and high-performance liquid chromatographic analysis. In-source collision-induced dissociation was used to optimize fragmentation to produce mass spectra consisting of the protonated molecule and two characteristic fragment ions of nearly equal intensity. Selected ion monitoring of three ions per quinolone yielded sensitive detection in catfish muscle extracts (estimated instrumental detection limits 0.8-1.7 ppb). The intensity ratios were used to confirm the presence of three of the quinolones based on the accurate agreement (< or equal to 10% deviation) between ratios derived from fortified catfish extracts and those from standard quinolones. MS/MS was used to increase the specificity and sensitivity of analysis. Scans using constant neural loss (CNL) of 18 mass units gave a sensitive response for the quinolones suggesting that CNL scans may be applicable to multiresidue screening for unknown quinolones. MS/MS with multiple reaction monitoring of the [MH - 18]+ transition for each quinolone yielded the highest sensitivity analysis in catfish extracts (estimated instrumental detection limits 0.08-0.16 ppb).

4-Quinolones↗

PubMed1997

A reference method for the analysis of aldosterone in blood by high-performance liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry.

A high-performance liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry (HPLC-APCI-MS/MS) reference method for the quantitation of aldosterone in serum and plasma has been developed. Samples were extracted with dichloromethane/diethyl ether, containing flumethasone as internal standard (IS). Chromatography was performed on a phenyl column using 50 mm ammonium formate (pH 7.1)/methanol (50/50, v/v) as mobile phase. Analysis was in negative-ionization mode by selected reaction monitoring (aldosterone m/z 359.2 --> 331.2; IS m/z 455.0 --> 379.0). The assay was linear over the range 15-500 pg/mL, with limits of detection and quantitation of 10 and 15 pg/mL, respectively. Imprecisions of the assay at 15, 20, 150, and 450 pg/mL were 18.5, 8. 8, 10.6, and 9.5%, respectively. The accuracy of the method ranged from 93.1 to 98.9% with absolute recoveries between 84.0 and 91.3% (aldosterone) and 88.0 and 92.3% (IS). We present a case study of a patient admitted, with suspected primary hyperaldosteronism, on the basis of a high radioimmunoassay (RIA) aldosterone concentration. The results suggest that RIA was unreliable, causing unnecessary patient discomfort and a costly 6-day hospital stay. The specific HPLC-API-MS/MS assay described offers the sensitivity and accuracy required to assess abnormal aldosterone production in hypertensive patients.

Aldosterone↗

PubMed2006

Surface oxidation of polyethylene using an atmospheric pressure glow discharge with liquid electrolyte cathode.

This study investigated the action of an atmospheric pressure air glow discharge (APGD) with aqueous electrolyte cathode onto the surface of polyethylene (PE) films. Distilled water and aqueous solutions of KCl and HCl were utilized as a cathode. The surface properties of PE were characterized by contact angle measurement followed by surface free energy calculation, Fourier transform infrared by attenuated total reflectance (FTIR-ATR), and XPS. After treating the PE surface, we observed OH groups, CO groups in ester, ketone, and carboxyl groups, and CO groups in unsaturated ketones and aldehydes. For a treatment time of 20 min and a discharge current of 40 mA, atomic concentrations of O and N were 12% and 2%, respectively, under distilled water application. Modification processes were able to improve the surface free energy of PE.

Journal Article↗

PubMed2005

Real-time flavor release from French fries using atmospheric pressure chemical ionization-mass spectrometry.

Flavor release from French fries was measured with atmospheric pressure chemical ionization-mass spectrometry (APCI-MS) using both assessors (in vivo) and a mouth model system (in vitro). Several volatiles measured with APCI were identified with MS-MS. The effect of frying time, salt addition, and an alternative process using superheated steam was determined on I(max) (maximum intensity of compounds) and on t(max) (time of maximum intensity). In vitro a "chewing" frequency of 0.60 Hz caused an increased t(max) for low molecular weight compounds compared to the other frequencies tested. Above 0.93 Hz further increase in the frequency did not affect t(max). Trends observed with in vivo experiments could be verified with in vitro experiments. I(max) correlated well with frying time. Addition of salt resulted in a decreased t(max), suggesting a salting-out effect. The alternative process caused a layer of oil on the surface, and this resulted in a higher t(max), but no effect on I(max) was found. This phenomenon may be critical for the sensory quality and would not have been observed with static volatile measurements, demonstrating the value of flavor release measurements.

Food Handling↗

PubMed2005

Atmospheric pressure coated-wall flow-tube study of acetone adsorption on ice.

An atmospheric pressure variant of the coated-wall flow-tube technique in combination with a Monte Carlo simulation is presented. In a performance test of simple first-order wall loss, the Monte Carlo simulation, which uses a simplified model of transport in laminar flow, reproduced results of an analytical solution of the transport equations in a flow tube. This technique was then used to investigate the reversible adsorption of acetone on ice films between 203 and 223 K and a surface coverage of below 5% of a formal monolayer. Simulation of the experimental uptake traces allowed retrieving an adsorption enthalpy of -46 +/- 3 kJ mol(-1) for acetone on ice, which is in good agreement with other static and flow-tube methods. For the experimental conditions adopted here, the transport of acetone molecules along the ice film is governed by equilibrium thermodynamics. Therefore, the surface accommodation coefficient, S(0), and the preexponential factor, tau(0), for the activated desorption cannot be independently determined. These two main microphysical parameters describing partitioning can rather be estimated through their relation to the adsorption entropy. A first estimate for S(0) of acetone on ice in the range of 0.004-0.043 is given.

Journal Article↗

PubMed2005

Decomposition mechanism of the anions generated by atmospheric pressure chemical ionization of nitroanilines.

The decomposition reaction mechanism of the anions generated by atmospheric pressure chemical ionization (APCI) mass spectrometry, in the negative mode, of nitroanilines and 2,4-dinitroanilines has been probed using quantum chemical calculations. The same process has been analyzed for the neutral counterparts and the simpler neutral and anionic nitrobenzenes. Our computations using density functional theory at the B3LYP/6-311++G(3df,2p) level demonstrate that the decomposition of the anion occurs in a two-stage process, involving an initial nitro-nitrite rearrangement followed by a NO-elimination leading to formation of a phenoxy radical anion derivative. The former is by far the rate-determining step. Calculations using the MP2 and CCSD(T)/6-311++G(d,p) levels also pointed out the same energy landscape. A similar mechanism has also been emphasized for the neutral counterparts. The effects of the amino and nitro groups as well as that of the negative charge on the nitro-nitrite interconversion are rather small and do not qualitatively modify the landscape of the pertinent energy surface and thereby the NO-loss mechanism.

Journal Article↗

PubMed2000

Dependence on the scattering angle of the electron temperature and electron density in thomson-scattering measurements on an atmospheric-pressure plasma jet

Electron temperature and electron density measurements were made in an atmospheric-pressure argon plasma jet by line-shape analysis of Thomson-scattered laser light. The dependence of electron temperature and electron density on the scattering angle was investigated. Measurements were made using incident laser wavelengths of 532 and 355 nm. At 532 nm, the electron-ion collision frequency exceeds the Landau damping rate for shallow scattering angles, and the electron plasma wave resonance structure in the Thomson line shape is broadened. This resulted in dramatic increase in the apparent electron temperature as a function of decreasing scattering angle. At 355 nm, collisions do not affect the Thomson line shape. In this case, an angular dependence of the measured electron temperature is not expected and was not observed. Data taken at 532 nm at larger scattering angles are consistent with the 355-nm results, and show that the electrons are not in thermodynamic equilibrium with the heavy particles.

Journal Article↗

PubMed2002

Rapidly tuning miniature transversely excited atmospheric-pressure CO2 laser.

An experimental study of a rapidly tuning miniature transversely excited atmospheric-pressure CO2 laser is reported. To rapidly shift laser wavelengths over selected transitions in the 9-11 microm wavelength region, we have utilized a high-frequency stepping motor and a diffraction grating. The laser is highly automated with a monolithic microprocessor controlled laser line selection. For the achievement of stable laser output, a system of laser excitation with a voltage of 10 kV, providing effective surface corona preionization and allowing one to work at various gas pressures, is utilized. Laser operation at 59 emission lines of the CO2 molecule rotational transition is obtained and at 51 lines, the pulse energy of laser radiation exceeds 30 mJ. The system can be tuned between two different rotational lines spanning the wavelength range from 9.2 to 10.8 microm within 10 ms.

Journal Article↗

PubMed1999

Interpretation of electrospray and atmospheric pressure chemical ionization mass spectra of 10-formyl-7,8-dihydrofolic acid and 5-formyl-5,6,7,8-tetrahydropteroic acid.

Interpretation of positive- and negative-ion electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) mass spectra of 10-formyl-7,8-dihydrofolic acid (10-FDHFA) and 5-formyl-5, 6,7,8-tetrahydropteroic acid (5-FTHPA) is discussed. ESI mass spectra enable unambiguous molecular weight (MW) determination. In addition to the determination of MW, APCI mass spectra also make possible structure elucidation of 10-FDHFA and 5-FTHPA. ESI and APCI are complementary ionization techniques and appear to be useful alternatives to conventional electron ionization (EI) for the structure elucidation of non-volatile carboxylic acids. Prior to mass spectral analysis, the acids investigated were separated by reverse-phase high-performance liquid chromatography (HPLC).

Atmospheric Pressure↗

PubMed1995

Estimation of ranolazine and eleven phase I metabolites in human plasma by liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry with selected-ion monitoring.

The estimation of ranolazine, a novel piperazine derivative, and eleven of its Phase I metabolites has been undertaken by liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry (LC-APCI-MS). Plasma samples, taken on day 5 of a multiple-dose study, were extracted by solid-phase extraction (SPE) and analysed, using a gradient HPLC system coupled to the APCI source of a Finnigan MAT TSQ 700 mass spectrometer. Metabolites were analysed in selected-ion monitoring (SIM) mode, using an instrument control language (ICL) procedure. The LC-MS combination allowed resolution of all eleven metabolites, including four hydroxylated metabolites and five unresolved components. The results from the linear regression showed good correlation (r2 > 0.980) for all the metabolites. Plasma concentrations indicated that three metabolites were present at levels higher than 10% of the parent compound.

Acetanilides↗

PubMed1977

Atmospheric pressure and idiopathic facial paralysis (Bell's palsy).

In a statistical study the onset of idiopathic facial paralysis (Bell's palsy) in 241 patients, observed in a 3-year period, is studied in relation to atmospheric pressure. The hypothesis of no association is not rejected. Neither is the hypothesis rejected of uniform distribution of the occurrence of Bell's palsy during the same period.

Atmospheric Pressure↗

PubMed1991

Chloride attachment negative-ion mass spectra of sugars by combined liquid chromatography and atmospheric pressure chemical ionization mass spectrometry.

A method has been developed for the rapid determination of sugars, including molecular weight measurements, using high-performance liquid chromatography coupled with negative-ion, atmospheric-pressure chemical-ionization mass spectrometry. The chromatography was carried out on a 250 x 4 mm I.D. column packed with 7 microns NH2-silica. The mobile phase consisted of a high percentage of methanol or acetonitrile with a small amount of chloroform. During the mass spectrometry, a strong base is formed from the polar solvent molecules by corona discharge, followed by ion-molecule reactions in the chemical ionization ion source (e.g. the methoxy anion is formed from methanol). This strong base reacts with the chloroform, generating chloride ions, which in turn react with the neutral sugar molecules as they elute from the chromatograph. The chloride ion and sugar interactions yield chloride-attachment ions, which are further stabilized by successive collisions. In this method, authentic monosaccharides and some oligosaccharides show dominant quasi-molecular ions, [M + Cl]-, with little fragmentation, and its particularly useful for the molecular weight determination of sugars.

Atmospheric Pressure↗

PubMed2000

A library of atmospheric pressure ionization daughter ion mass spectra based on wideband excitation in an ion trap mass spectrometer.

A searchable library of MS/MS spectra obtained using a quadrupole ion trap mass spectrometer and electrospray or atmospheric pressure chemical ionization is presented. The application of wideband excitation (activation) and normalized collision energy leads to highly reproducible mass spectra which are searched using the NIST algorithm. Flow injection and LC/MS/MS applications of this powerful technique in the biomedical (diastereoisomeric steroids, morphine glucuronides, isovalerylcarnitine) and environmental (pirimicarb and desmethyl-pirimicarb) areas are described.

Algorithms↗

PubMed2003

Electron ionization and atmospheric pressure photochemical ionization in gas chromatography-mass spectrometry analysis of amino acids.

The mass spectra of tert-butyldimethylsilyl (TBDMS) derivatives of 17 amino acids were obtained using electron ionization (EI) and atmospheric pressure photochemical ionization (APPhCI) mass spectrometry. The APPhCI mass spectra for all of the derivatives except arginine were shown to consist of only molecular [M](+.) and quasimolecular [MH](+) ions whereas, in the case of EI, the compounds in question underwent a drastic fragmentation. The application of APPhCI to gas chromatography-mass spectrometry enables a reliable identification of the TBDMS derivatives of amino acids in a mixture, even if its components are only partially resolved, due to the unique molecular masses for each compound. Comparison of the respective positive-ion chemical ionization (PICI) mass spectra available in the literature with APPhCI spectra has shown that, in the case of PICI, unlike APPhCI, noticeable fragmentation occurs.

Amino Acids↗