PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “ATMOSPHERIC PRESSURE”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12Linked to original sources
PubMed1999

Column performance and stability for high-speed vacuum-outlet GC of volatile organic compounds using atmospheric pressure air as carrier gas.

The development of lightweight, portable GC instrumentation is handicapped by the need for compressed carrier gas to drive the separation. The use of air as carrier gas eliminates the need for compressed gas tanks. If a vacuum pump is used to pull carrier gas and injected samples through the column, atmospheric pressure air can be used as carrier gas. Vacuum outlet operation also improves performance for high-speed separations by reducing detector dead time and by shifting optimal carrier gas velocity to higher values. Under vacuum outlet conditions using atmospheric pressure air as carrier gas, a 6-m-long, 0.25-mm-i.d. capillary column can generate approximately 12,500 theoretical plates, and a 12-m-long column can generate approximately 44,000 plates but with a 3-4-fold increase in separation time. The principal issues in column selection for high-speed GC with air as a carrier gas are efficiency and stability. Several bonded and nonbonded stationary phases were evaluated for use with air as carrier gas in the analysis of volatile organic compounds of interest in airmonitoring applications. These include dimethylpolysiloxane, 50% phenyl-50% methyl polysiloxane, 50% cycanopropylphenyl-50% methyl polysiloxane, trifluoropropyl polysiloxane, poly(ethylene glycol), and dicyanoallyl polysiloxane (nonbonded). The dimethyl polysiloxane and the trifluoropropyl polysiloxane columns showed good efficiency and no significant deterioration after 5 days of continuous operation with air as carrier gas. The 50% phenyl-50% methyl polysiloxane and the 50% cycanopropylphenyl-50% methyl polysiloxane columns showed poorer efficiency, and the poly(ethylene glycol) and dicyanoallyl polysiloxane columns showed excessive deterioration in air.

Air↗
PubMed2002

Determination of selected sulfonamide antibiotics and trimethoprim in manure by electrospray and atmospheric pressure chemical ionization tandem mass spectrometry.

A method for the determination of sulfonamides and trimethoprim in the complex matrix liquid manure has been developed using reversed-phase liquid chromatography and atmospheric pressure chemical ionization (APCI) tandem mass spectrometry. A comparison was made between electrospray and atmospheric pressure chemical ionization. APCI proved to be more robust and less sensitive to matrix effects. High-performance liquid chromatographic (HPLC) separation of the analytes was achieved in less than 7 min. The compounds were extracted with ethyl acetate and the extracts were cleaned up by solid-phase extraction on an aminopropyl column. Recoveries were not dependent on the concentration level. The mean recoveries were as follows: trimethoprim 79.0%, sulfadiazine 80.5%, N(4)-acetylsulfadiazine 91.0%, sulfamerazine 78.6%, sulfadimidine 77.2% and sulfamethoxazole 82.8%. Linearity was established over a concentration range of 5 to 5000 microg/kg with correlation coefficients greater than 0.99. The method had a limit of quantitation (LOQ) of 5 microg/kg manure.

Animals↗
PubMed2006

The atmospheric pressure Meerwein reaction.

We have already shown that the in-vacuum gas-phase Meerwein reaction of (thio)acylium ions is general in nature and useful for class-selective screening of cyclic (thio)epoxides. Herein we report that this gas-phase reaction can also be performed efficiently at atmospheric pressure under both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) conditions. This alternative expands the range of molecules that can be reacted by gas-phase Meerwein reaction. Phenyl epoxide, thiirane, 3-methoxy-2,2-dimethyloxirane, propylene oxide, 2,2'-bioxirane, trans-1,3-diphenyl-2,3-epoxypropan-1-one, epichloridrine and propylene oxide are shown to react efficiently in both ESI and APCI conditions. Tetramethylurea (TMU) and (thio)TMU were both used as dopants, being co-injected with either toluene, acetonitrile or methanol solutions of the (thio)epoxides, with similar results. In both ESI and APCI, (thio)TMU is protonated preferentially, and these labile species dissociate promptly to yield (CH3)2N-C+=O and (CH3)2NCS+, which are the least acidic and most reactive (thio)acylium ions so far tested in the gas-phase Meerwein reaction. Under the low-energy ESI conditions set to favor both the formation of the (thio)acylium ion and ion/molecule reactions, (CH3)2NCO(S)+ react competitively with (thio)TMU to form acylated (thio)TMU and with the (thio)epoxide to form the characteristic Meerwein products. Enhanced selectivity in structural characterization or for the screening of (thio)epoxides is achieved by performing on-line collision-induced dissociation of Meerwein products, particularly for the more structurally complex (thio)epoxides.

Journal Article↗
PubMed2004

Origin of fluctuations in atmospheric pressure arc plasma devices.

Fluctuations in arc plasma devices are extremely important for any technological application in thermal plasma. The origin of such fluctuations remains unexplained. This paper presents a theory for observed fluctuations in atmospheric pressure arc plasma devices. A qualitative explanation for observed behavior on atmospheric pressure arc plasma fluctuations, reported in the literature, can be obtained from the theory. The potential of the theory is demonstrated through comparison of theoretical predictions with reported experimental observations.

Journal Article↗
PubMed1981

Atmospheric pressure ionization mass spectrometry: the routine determination of 2,4,5-trichlorophenoxyacetic acid and its metabolites.

This study demonstrated the utility of negative ion atmospheric pressure ionization mass spectrometry for the routine quantitation of 2,4,5-trichlorophenoxyacetic acid and its glycine and taurine amide metabolites in mouse blood, urine and feces samples. The quantitation of 2,4,5-trichlorophenoxyacetic acid in blood follows a short cleanup procedure and used 2,4,5-trichlorophenoxy-13C6-acetic acid as the stable label isotope diluent. A more extensive cleanup procedure utilizing high-pressure liquid chromatography was required for the determination of 2,4,5-trichlorophenoxyacetic acid and its two metabolites in urine and feces. The glycine amide metabolite was quantitated by the 13C stable isotope diluent method. The taurine amide relied on an initial separation step followed by using a second 2,4,5-trichlorophenoxy-13C6-acetic acid spike fot its isotope diluent. Alkaline hydrolysis of the metabolites, followed by methylation, allowed the methyl ester of 2,4,5-trichlorophenoxyacetic acid to be solely used as the analyte in the negative ion atmospheric pressure ionization mass spectrometry quantitation step.

2,4,5-Trichlorophenoxyacetic Acid↗
PubMed1996

Eustachian tube function and middle ear barotrauma associated with extremes in atmospheric pressure.

Eustachian tube (ET) function was studied by means of sonotubometry and tubotympano-aerodynamography (TTAG) prior to and following exposure to hypobaric or hyperbaric conditions. Forty normal adults were subjected to hypobaric pressure. Fifty adults who underwent hyperbaric oxygen (HBO) therapy also were studied. Following hypobaric exposure, 14 of 80 ears (17.5%) exhibited middle ear barotrauma. Following hyperbaric exposure, 34 of 100 ears (34%) exhibited middle ear barotrauma. Dysfunction of the ET, characterized by altered active and passive opening capacity, was more prevalent following exposure to extremes in atmospheric pressure compared to baseline. The ET function, which was impaired after the first HBO treatment, improved gradually over the next 2 hours. Overall, however, ET function was worse after the seventh treatment. The patients who developed barotrauma exhibited worse ET function prior to hypobaric or hyperbaric exposure. Thus, abnormal ET function can be used to predict middle ear barotrauma prior to exposure to hypobaric or hyperbaric atmospheric pressure.

Adult↗
PubMed2002

Design and performance of an atmospheric pressure inlet system for lithium ion attachment mass spectrometry.

We designed a simple and efficient inlet system to act as an interface between samples at atmospheric pressure and the high vacuum inside a mass spectrometer. The newly designed stainless steel orifice leak sample inlet system is simple and rugged and fulfills all the basic requirements. With this inlet system coupled with a lithium ion attachment mass spectrometer, it is possible to detect any chemical species at atmospheric pressure, including radical intermediates, on a real-time basis. For illustrative purposes, the sampling efficiency of the inlet probe coupled with a lithium ion attachment mass spectrometer is discussed for laboratory air and polyethylene pyrolysis.

Journal Article↗
PubMed2004

Screening, library-assisted identification and validated quantification of 23 benzodiazepines, flumazenil, zaleplone, zolpidem and zopiclone in plasma by liquid chromatography/mass spectrometry with atmospheric pressure chemical ionization.

A liquid chromatographic/mass spectrometric assay with atmospheric pressure chemical ionization (LC/APCI-MS) is presented for fast and reliable screening and identification and also for precise and sensitive quantification in plasma of the 23 benzodiazepines alprazolam, bromazepam, brotizolam, camazepam, chlordiazepoxide, clobazam, clonazepam, diazepam, flunitrazepam, flurazepam, desalkylflurazepam, lorazepam, lormetazepam, medazepam, metaclazepam, midazolam, nitrazepam, nordazepam, oxazepam, prazepam, temazepam and tetrazepam, triazolam, their antagonist flumazenil and the benzodiazepine BZ1 (omega 1) receptor agonists zaleplone, zolpidem and zopiclone. It allows confirmation of the diagnosis of an overdose situation and monitoring of psychiatric patients' compliance. The analytes were isolated from plasma using liquid-liquid extraction and were separated on a Merck LiChroCART column with Superspher 60 RP Select B as the stationary phase. Gradient elution was performed using aqueous ammonium formate and acetonitrile. After screening and identification in the scan mode using the authors' LC/MS library, the analytes were quantified in the selected-ion monitoring mode. The quantification assay was fully validated. It was found to be selective proved to be linear from sub-therapeutic to over therapeutic concentrations for all analytes, except bromazepam. The corresponding reference levels the assay's accuracy and precision data for all studied substances are listed. The accuracy and precision data were within the required limits with the exception of those for bromazepam. The analytes were stable in frozen plasma for at least 1 month. The validated assay was successfully applied to several authentic plasma samples from patients treated or intoxicated with various benzodiazepines or with zaleplone, zolpidem or zopiclone. It has proven to be appropriate for the isolation, separation, screening, identification and quantification of the drugs mentioned above in plasma for clinical toxicology, e.g. in cases of poisoning, and forensic toxicology, e.g. in cases of driving under the influence of drugs.

Anti-Anxiety Agents↗
PubMed2006

Characterizing electrospray ionization using atmospheric pressure ion mobility spectrometry.

Reduced flow rate electrospray ionization has been proven to provide improved sensitivity, less background noise, and improved limits of detections for ESI-MS analysis. Miniaturizing the ESI source from conventional electrospray to microelectrospray and further down to nanoelectrospray has resulted in higher and higher sensitivity; however, when effects of flow rate were investigated for atmospheric pressure ESI-IMS using a nanospray emitter, a striking opposite result was observed. The general tendency we observed in ESI-IMS was that higher flow rate offered higher ion signal intensity throughout a variety of conditions investigated. Thus, further efforts were undertaken to rationalize these contradictory results. It is well accepted that decreased flow rate increases both ionization efficiency and transmission efficiency, thus improving ion signal in ESI-MS. However, our study revealed that decreased flow rate results in decreased ion signal because ion transfer is constant, no matter how flow rate changes in ESI-IMS. Since ion transfer is constant in atmospheric pressure ESI-IMS, ionization efficiency can be studied independently, which otherwise is not possible in ESI-MS in which both ionization efficiency and transmission efficiency vary as conditions alter. In this article, we present a systematic study of signal intensity and ionization efficiency at various experimental conditions using ESI-IMS and demonstrate the ionization efficiency as a function of flow rate, analyte concentration, and solvent composition.

Atmospheric Pressure↗
PubMed2003

Ethanol potentiation of glycine receptors expressed in Xenopus oocytes antagonized by increased atmospheric pressure.

BACKGROUND: Behavioral and biochemical studies indicate that exposure to 12 times normal atmospheric pressure (12 ATA) of helium-oxygen gas (heliox) is a direct, selective ethanol antagonist. The current study begins to test the hypothesis that ethanol acts by a common mechanism on ligand-gated ion channels by expanding previous hyperbaric investigations on gamma-aminobutyric acid type A (GABA(A)) receptors (GABA(A)Rs) at the biochemical level to alpha(1)glycine (GlyRs) expressed in Xenopus oocytes. METHODS: Oocytes expressing wild-type alpha(1) homomeric GlyRs were voltage-clamped (-70 mV) and tested in the presence of glycine (EC(2)) +/- ethanol (50-200 mM) under 1 ATA control and 3 to 12 ATA heliox conditions. Glycine concentration response curves, strychnine/glycine interactions, and zinc (Zn2+) modulation of GlyR function was also tested. RESULTS: Pressure reversibly antagonized the action of ethanol. The degree of antagonism increased as pressure increased. Pressure did not significantly alter the effects of glycine, strychnine, or Zn2+, indicating that ethanol antagonism by pressure cannot be attributed to alterations by pressure of normal GlyR function. The antagonism did not reflect tolerance to ethanol, receptor desensitization, or receptor rundown. CONCLUSION: This is the first use of hyperbarics to investigate the mechanism of action of ethanol in recombinant receptors. The findings indicate that pressure directly and selectively antagonizes ethanol potentiation of alpha(1)GlyR function in a reversible and concentration- and pressure-dependent manner. The sensitivity of ethanol potentiation of GlyR function to pressure antagonism indicates that ethanol acts by a common, pressure-antagonism-sensitive mechanism in GlyRs and GABA(A)Rs. The findings also support the hypothesis that ethanol potentiation of GlyR function plays a role in mediating the sedative-hypnotic effects of ethanol.

Allosteric Regulation↗
PubMed2003

Atmospheric pressure matrix-assisted laser desorption/ionisation ion trap mass spectrometry of synthetic polymers: a comparison with vacuum matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry.

Atmospheric pressure matrix-assisted laser desorption/ionisation quadrupole ion trap (AP-MALDI/QIT) mass spectrometry has been investigated for the analysis of polyethylene glycol (PEG 1500) and a hyperbranched polymer (polyglycidol) in the presence of alkali-metal salts. Mass spectra of PEG 1500 obtained at atmospheric pressure showed dimetallated matrix/analyte adducts, in addition to the expected alkali-metal/PEG ions, for all matrix/alkali-metal salt combinations. The relative intensities of the desorbed ions were dependent on the matrix, the alkali-metal salt added to aid cationisation and the ion trap interface conditions [capillary temperature, in-source collisionally-induced dissociation (CID)]. These data indicate that the adducts are rapidly stabilised by collisional cooling enabling them to be transferred into the ion trap. Experiments using identical sample preparation conditions were carried out on a vacuum MALDI time-of-flight (ToF) mass spectrometer. In all cases, vacuum MALDI-ToF spectra showed only alkali-metal/PEG ions and no matrix/analyte adducts. The tandem mass spectrometry (MS/MS) capability of the ion trap has been demonstrated for a lithiated polyglycol yielding a rich fragment-ion spectrum. Analysis of the hyperbranched polymer polyglycidol by AP-MALDI/QIT reveals the characteristic ion series for these polymers as also observed under vacuum MALDI-ToF conditions.

Journal Article↗
PubMed2000

[Seasonal variation and influence of atmospheric pressure diurnal fluctuations on occurrence of acute complications in patients with stomach and duodenal ulcer].

Although there is rich literature concerning seasonal fluctuations of incidence of peptic ulcer, no one can find so many data on acute complications of this disease--bleedings and perforations. There is also only little information saying about the role of meteorological factors that can take part in occurrence of the mentioned complications. This study aimed to analyze the seasonal variation (in calendar months, quarters of the year and calendar seasons--winter, spring, summer, autumn) of peptic ulcer bleeding and perforations as well as the influence of atmospheric pressure diurnal fluctuations on the occurrence of these diseases. The conducted study was retrospective and based on data of patients admitted to III Department of General Surgery of the Jagiellonian University Medical School in Cracow. Altogether, from 1993 to 1997--26 patients with peptic gastroduodenal ulcer bleeding were admitted. 220 bleedings were endoscopically proven (6 patients did not agree for gastroscopy and were excluded from further analysis). 157 patients were treated because of peptic ulcer perforation at the same time and all of them underwent surgical procedure during which perforation was proven. The chi 2 test was used in order to verify our statistic hypothesis (p = 0.05). The examination did not show any significant seasonal variation of the studied complications. Neither hemorrhage nor perforation presented any seasonal prevalence. As for calendar months, quarters and calendar seasons (p > 0.01; p > 0.02; p > 0.02 respectively). However, the study confirmed the role of atmospheric pressure falls in the occurrence of both: bleeding and perforation of peptic ulcer (p < 0.001). 153 patients with bleeding were admitted on days with decreasing pressure, while 67 when pressure was going up. Similarly as for perforations--94 with falling down to 33 with growing up pressure.

Aged↗
PubMed2003

Feasibility of atmospheric pressure desorption/ionization on silicon mass spectrometry in analysis of drugs.

The feasibility of atmospheric pressure desorption/ionization on silicon mass spectrometry (AP-DIOS-MS) for drug analysis was investigated. It was observed that only compounds with relative high proton affinity are efficiently ionized under AP-DIOS conditions. The limits of detection (LODs) achieved in MS mode with midazolam, propranolol, and angiotensin II were 80 fmol, 20 pmol, and 1 pmol, respectively. In MS/MS mode the LODs for midazolam and propranolol were 10 fmol and 5 pmol, respectively. The good linearity (r(2) > 0.991), linear dynamic range of 3 orders of magnitude, and reasonable repeatability showed that the method is suitable for quantitative analysis.

Acetaminophen↗
PubMed2003

Fragmentation of sialylated carbohydrates using infrared atmospheric pressure MALDI ion trap mass spectrometry from cation-doped liquid matrixes.

Infrared atmospheric pressure matrix-assisted laser desorption/ionization on an ion trap mass spectrometer is used to study sialylated oligosaccharides desorbed from the liquid phase. Glycerol doped with various cations provides the opportunity to produce cation-adducted intact molecular ions of sugars. Distinct combinations of cations allow for sialic acid stabilization, as well as differential cleavage, resulting in more complete fragmentation coverage of the oligosaccharide. Alkali and transition metal cations are utilized to create three distinct molecular ion species, involving the adduction of a singly charged cation, two singly charged cations, or a doubly charged cation. From these different molecular ion types, complementary sequence, branching, and linkage information for sialylated oligosaccharides can be deduced.

Atmospheric Pressure↗
PubMed2000

Combined protocol for the analysis of polycyclic aromatic hydrocarbons (PAHs) and polychlorobiphenyls (PCBx) from sediments using focussed microwave assisted (FMW) extraction at atmospheric pressure.

A microwave-assisted protocol has been developed using focussed microwaves at atmospheric pressure for the extraction of PAHs and PCBs from sediments. It combines extraction and purification assisted by microwaves. This protocol has been applied to the quantification of 12 individual PAHs, 8 individual PCBs and 8 PCB coeluted mixtures from two Standard Reference Materials and one natural sediment. The results for both classes of compounds (PAHs and PCBs) are good in terms of recoveries, which are always greater than 70% and in most cases around 100%. The reproducibility is also good with coefficients of variation below 10% in most cases. This protocol has the great advantage of saving time, the time dedicated to the preparation / extraction assisted by microwaves being reduced to less than half an hour.

Atmospheric Pressure↗
PubMed2001

Analysis of phospholipid molecular species by liquid chromatography--atmospheric pressure chemical ionisation mass spectrometry of diacylglycerol nicotinates.

A method using liquid chromatography - atmospheric pressure chemical ionisation mass spectrometry was evaluated for determining the molecular species composition of phospholipids (phosphatidylcholines from soybean, egg yolk and bovine liver) after conversion to diacylglycerol nicotinate derivatives. The structures could be deduced from pseudo-molecular ions ([MH-123](+)) and three pairs of monoacyl containing fragment ions. All molecular species in mixed peaks were readily identified and many minor components, earlier not encountered in the samples under investigation, were identified. Acyl chain regioisomers were readily distinguished by the ratio of the [MH-RCHCO](+) ions. Molecular species differing only in the position of the double bonds in one polyunsaturated acyl chain were separated on the basis of retention times. A half quantitative estimation of the molecular species composition of complex samples was achieved by a combination of UV detection and, for mixed peaks, the areas of [MH-123](+) ions.

Animals↗
PubMed2005

Determination of methadone, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine, 2-ethyl-5-methyl-3,3-diphenylpyraline and methadol in meconium by liquid chromatography atmospheric pressure chemical ionization tandem mass spectrometry.

This paper details a validated liquid chromatography atmospheric pressure chemical ionization tandem mass spectrometry (LC-APCI-MS/MS) method for the quantification of methadone, and its metabolites 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), 2-ethyl-5-methyl-3,3-diphenylpyraline (EMDP) and methadol in human meconium. Limits of detection (LOD) were determined to be 1.0 ng/g for methadone, EDDP and EMDP and 2.5 ng/g for methadol. The limits of quantitation (LOQ) for methadone, EDDP, EMDP were 5 and 25 ng/g for methadol. Linearity ranged from 5.0 to 500 ng/g. Following solid-phase extraction, no matrix effect was observed. This method proved to be suitable for the quantification of methadone, EDDP and EMDP and the semi-quantitation of methadol in meconium. Literature review revealed no other published LC-APCI-MS/MS method for the detection of methadone and its three main metabolites in meconium specimens.

Atmospheric Pressure↗