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 343 records · Page 19Linked to original sources
PubMed2002

Atmospheric pressure photoionization mass spectrometry. Ionization mechanism and the effect of solvent on the ionization of naphthalenes.

The ionization mechanism in dopant-assisted atmospheric pressure photoionization and the effect of solvent on the ionization efficiency was studied using 7 naphthalenes and 13 different solvent systems. The ionization efficiency was 1-2 orders of magnitude higher with dopant than without, indicating that the photoionization of the dopant initiates the ionization process. In positive ion mode, the analytes were ionized either by charge exchange or by proton transfer. Charge exchange was favored for low proton affinity solvents (water, hexane, chloroform), whereas the addition of methanol or acetonitrile to the solvent initiated proton transfer. In negative ion mode, the compounds with high electron affinity were ionized by electron capture or by charge exchange and the compounds with high gas-phase acidity were ionized by proton transfer. In addition, some oxidation reactions were observed. All the reactions leading to ionization of analytes in negative ion mode are initiated by thermal electrons formed in photoionization of toluene. The testing of different solvents showed that addition of buffers such as ammonium acetate, ammonium hydroxide, or acetic acid may suppress ionization in APPI. The reactions are discussed in detail in light of thermodynamic data.

Atmospheric Pressure↗
PubMed2005

Preparation of a reticulated polyurethane foam grafted with poly(acrylic acid) through atmospheric pressure plasma treatment and its lysozyme immobilization.

We successfully introduced peroxide groups onto the surface of PU(Polyurethane) foam(10 PPI) through one atmospheric pressure plasma treatment and sequentially grafted PAAc(poly(acrylic acid)) on the surface of PU through radical copolymerization. The plasma treatment can generate large amount of peroxides on the surface of PU foam and the peroxide groups act as initiators for further grafting of PAAc in the monomer solution. To introduce large amount of peroxides on the surface of PU foam, we studied the effect of plasma rf-power and treatment time on the maximum grafting of PAAc. Through this study, we found that the optimum plasma treatment condition was the rf-power of 100 W and the treatment time of 100 s. On the other hand, we also studied the effect of graft reaction conditions such as temperature, monomer concentration and reaction time on the change of grafting degree (GD). The GD increased with increasing temperature and increased with reaction time before it leveled off at 3 h after reaction started. At low concentration of AAc, the GD was very low but it showed a maximum at the monomer concentration between 60 and 70%. The surface of the modified PU foam was qualitatively and quantitatively analyzed through the use of FT-IR and weight measurement, respectively. We also observed the surface change before and after plasma induced graft co-polymerization through photo and SEM analysis. Finally, we confirmed that the PU foams grafted with PAAc successfully immobilized lysozyme and other proteins from hen egg white.

Acrylic Resins↗
PubMed2004

Determination of a novel substance P inhibitor in human plasma by high-performance liquid chromatography with atmospheric pressure chemical ionization mass spectrometric detection using single and triple quadrupole detectors.

Methods based on high-performance liquid chromatography (HPLC) with atmospheric-pressure chemical ionization (APCI) mass spectrometric (MS) detection using either single (MS) or triple (MS/MS) quadrupole mass spectrometric detection for the determination of (2R)-[1(R)-(3,5-bis-trifluoromethylphenyl)ethoxy]-3(S)-(4-fluoro-phenyl)morpholin-4-ylmethyl]-5-oxo-4,5-dihydro-[1,2,4]triazol)methyl morpholine (Aprepitant, Fig. 1) in human plasma has been developed. Aprepitant (I) and internal standard (II, Fig. 1) were isolated from the plasma matrix buffered to pH 9.8 using a liquid-liquid extraction with methyl-t-butyl ether (MTBE). The analytes were separated on a Keystone Scientific's Javelin BDS C-8 2 mm x 4.6 mm 3 microm guard column coupled to BDS C-8 50 mm x 4.6 mm 3 microm analytical column, utilizing a mobile phase of 50% acetonitrile and 50% water containing 0.1% formic acid and 10 mM ammonium acetate delivered at a flow rate of 1 ml/min. The single quadrupole instrument was operated in a single ion monitoring (SIM) mode analyzing the protonated molecules of Aprepitant and II at m/z 535 and 503, respectively. The triple quadrupole mass spectrometer was operated in multiple reaction monitoring mode (MRM) monitoring the precursor --> ion combinations of m/z 535 --> 277 and 503 --> 259 for Aprepitant and II, respectively. The linear calibration range for both single and triple quadrupole detectors was from 10 to 5000 ng/ml of plasma with coefficients of variation less than 8% at all concentrations. Both single and triple quadrupole instruments yielded similar precision and accuracy results. Matrix effect experiments performed on both instruments demonstrated the absence of any significant change in ionization of the analytes when comparing neat standards to analytes in the presence of plasma matrix. Both instruments were used successfully to support numerous clinical trials of Aprepitant.

Aprepitant↗
PubMed2004

Rapid simultaneous determination of o-phenylphenol, diphenyl, thiabendazole, imazalil and its major metabolite in citrus fruits by liquid chromatography-mass spectrometry using atmospheric pressure photoionization.

A simple and rapid simultaneous analytical method of four post-harvest fungicides, o-phenylphenol (OPP), diphenyl (DP), thiabendazole (TBZ), imazalil (IMZ) and its major metabolite R14821 (IMZ-M) in citrus fruits was developed. These compounds were extracted under basic conditions with diethyl ether. The organic layer was washed with water and evaporated at moderate pressure adding methanol. These compounds were determined by liquid chromatography-mass spectrometry (LC-MS) using atmospheric pressure photoionization (APPI). The recoveries of the five compounds added to citrus fruits at 1 microg/g ranged from 67 to 100%, with relative standard deviations (R.S.D.) ranging from 2 to 8%. The detection limits (S/N = 3) were 0.01 microg/g and 0.05 microg/g (DP).

Atmospheric Pressure↗
PubMed2002

Real-time monitoring of thermal flavor generation in skim milk powder using atmospheric pressure chemical ionization mass spectrometry.

The feasibility of monitoring volatile flavor compounds formed by thermal treatment of skimmed milk powder in real time by atmospheric pressure chemical ionization mass spectrometry (APCIMS) was established. Skim milk powder samples were heated isothermally (70 to 120 degrees C) at different moisture contents (2.2 and 12.7 g water/100 g dry solids). Headspace was sampled and analyzed continuously in full scan mode (30-180 amu) by APCIMS. The identity of the volatile compounds monitored by APCIMS was confirmed by coupled GC-EI-APCIMS. The concentration measured by the APCIMS was the net effect of three processes, namely formation of the compound, partition from the skim milk powder into the gas phase, and dilution due to the headspace sampling method used. Preliminary experiments established that the technique could follow the effects of heating temperature and moisture content on the formation of selected compounds from skim milk powder.

Animals↗
PubMed2006

Minimum proton affinity for efficient ionization with atmospheric pressure desorption/ionization on silicon mass spectrometry.

We performed a systematic study using a set of compounds with different proton affinities (PAs) on the ionization in atmospheric pressure desorption/ionization on silicon mass spectrometry (AP-DIOS-MS). The compounds studied included various aromatic molecules of different sizes. The PAs of these compounds were calculated using ab initio and hybrid density functional theory calculations at the B3LYP/6-31G(d) level of theory. We observed that only compounds with relatively high PAs above a threshold value of 920-950 kJ/mol were efficiently ionized as protonated molecules under AP-DIOS conditions and produced very clean mass spectra.

Adsorption↗
PubMed2000

Mass spectrometric study of randomly methylated beta-cyclodextrins using ionspray, atmospheric pressure chemical ionization and matrix-assisted laser desorption/ionization.

Mixtures of methylated beta-cyclodextrins were characterized using three different methods of mass spectrometry: ionspray, atmospheric pressure chemical ionization (APCI) and matrix-assisted laser desorption/ionization (MALDI). Each of these methods allows a fast and simple determination of the degree of substitution, and can provide evidence for differences in the methylation of batches which have very similar global degrees of substitution. The three methods are in good qualitative agreement, but there are systematic differences in the quantitative results for the percentages of the various methylated molecules present in a batch. This is attributed to ionization yields which increase with the number of methyl groups, with different slopes for the different methods.

Atmospheric Pressure↗
PubMed2000

Application of spectral libraries for high-performance liquid chromatography-atmospheric pressure ionisation mass spectrometry to the analysis of pesticide and explosive residues in environmental samples.

The coupling of high-performance liquid chromatography (HPLC) and atmospheric pressure ionisation mass spectrometry (API-MS) seems to be the method of choice if good separation and selective detection of semi-volatile, thermolabile, and polar substances is required. Libraries of mass spectra will make the identification of unknown substances in complex environmental samples easier and more user-friendly. Unfortunately, existing GC-MS libraries are not applicable to HPLC-API-MS analysis. Thus, new and extensive mass spectral libraries were constructed. Several investigations of chromatographic (composition and salt concentration of the eluent) as well as mass spectrometric (orifice voltage) parameters and a few applications of real environmental samples are used to discuss the possibilities and limits of these libraries.

Atmospheric Pressure↗
PubMed1993

Determination of pilocarpine in aqueous humour by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.

A new method has been developed for rapid analysis and determination of pilocarpine in aqueous humour using liquid chromatography-atmospheric pressure chemical ionization mass spectrometry. The chromatography was carried out on a reversed-phase phenyl column with 0.1% acetic acid-acetonitrile (95:5, v/v). Pilocarpine and its analogues, isopilocarpine, pilocarpic acid and isopilocarpic acid, were separated. An aqueous humour sample was deproteinized with methanol. After evaporation, the residue was dissolved in the mobile phase. The method was applied to the analysis of the metabolite in aqueous humour after the topical application of 2% pilocarpine (w/v) eye-drops. The main metabolite, pilocarpic acid, was easily identified. The protonated molecular ion of pilocarpine was used for the determination. The calibration curve had a good linearity within the concentration range investigated (2 ng to 10 micrograms/ml). The limit of determination was estimated to be an aqueous humour concentration of ca. 2 ng/ml. The method was applied to the determination of unchanged pilocarpine after the topical application of 2% pilocarpine (w/v) eye-drops.

Animals↗
PubMed2004

Quantitation of lysergic acid diethylamide in urine using atmospheric pressure matrix-assisted laser desorption/ionization ion trap mass spectrometry.

A quantitative method was developed for analysis of lysergic acid diethylamide (LSD) in urine using atmospheric pressure matrix-assisted laser desorption/ionization ion trap mass spectrometry (AP MALDI-ITMS). Following solid-phase extraction of LSD from urine samples, extracts were analyzed by AP MALDI-ITMS. The identity of LSD was confirmed by fragmentation of the [M + H](+) ion using tandem mass spectrometry. The quantification of LSD was achieved using stable-isotope-labeled LSD (LSD-d(3)) as the internal standard. The [M + H](+) ion fragmented to produce a dominant fragment ion, which was used for a selected reaction monitoring (SRM) method for quantitative analysis of LSD. SRM was compared with selected ion monitoring and produced a wider linear range and lower limit of quantification. For SRM analysis of samples of LSD spiked in urine, the calibration curve was linear in the range of 1-100 ng/mL with a coefficient of determination, r(2), of 0.9917. This assay was used to determine LSD in urine samples and the AP MALDI-MS results were comparable to the HPLC/ ESI-MS results.

Atmospheric Pressure↗
PubMed2000

Simultaneous determination of urinary free cortisol and 6beta-hydroxycortisol by liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometry and its application for estimating hepatic CYP3A induction.

A reversed-phase high-performance liquid chromatography coupled to atmospheric pressure chemical ionization tandem mass spectrometry (HPLC-APCI-MS-MS) assay was developed to simultaneously determine monkey urinary free cortisol (C) and 6beta-hydroxycortisol (6beta-OHC) in 8 min. Urine sample (0.5 ml) containing fludrocortisone acetate (F-C) as the internal standard was extracted with ethyl acetate for 5 min with an extraction efficiency of 90% and 75% for C and 6beta-OHC, respectively. A Perkin-Elmer Sciex API 3000 triple quadruple instrument was used for mass spectrometric detection and the column eluent was directed to a heated nebulizer probe. The assay was linear over the range 0.25-10 microM for each analyte. The intra- and inter-day relative standard deviation (RSD) over the entire concentration range for both analytes was less than 10%. Accuracy determined at three concentrations (0.8, 2.0 and 8.0 microM) ranged between 95.5 and 108%. The method described herein is suitable for the rapid and efficient measurement of 6beta-OHC/C ratio in Rhesus monkey urine following administration of known hepatic CYP3A inducers and can be used to estimate potential CYP3A induction by drug candidates in the process of early drug development.

Animals↗
PubMed2001

Highly sensitive determination of TS-962 (HL-004), a novel acyl-CoA:cholesterol acyltransferase inhibitor, in rat and rabbit plasma by liquid chromatography and atmospheric pressure chemical ionization-tandem mass spectrometry combined with a column-switching technique.

A quantitative bioanalytical method with excellent specificity using liquid chromatography (LC) atmospheric pressure chemical ionization-tandem mass spectrometry (APCI-MS-MS) combined with a column-switching technique has been developed for the highly sensitive and reliable determination of TS-962 (HL-004), a novel acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, in rat and rabbit plasma. The method involves protein precipitation of a 25-microl aliquot of plasma sample with eight volumes of methanol containing a deuterium-labeled internal standard, the direct injection of a methanolic supernatant into the analytical instrumentation with no sample evaporation and reconstitution steps, automated on-line clean-up on a C18 short trapping column (10 mm x 4.0 mm I.D.) followed by separation on a C18 analytical column (50 mm x 4.6 mm I.D.), and detection with APCI-MS-MS using m/z 448 ([M+H]+) as a precursor ion and m/z 178 as a product ion in a selected reaction monitoring mode. The lower limit of quantification was 1 ng/ml, and good linearity of the calibration graph was obtained in the range of 1 to approximately 490 ng/ml with excellent reliability. The developed method enabled pharmacokinetic profiles to be determined for rats and rabbits with sequential plasma collection from an individual animal.

Acetamides↗
PubMed2005

Analysis of amphetamines and fentanyls by atmospheric pressure desorption/ionization on silicon mass spectrometry and matrix-assisted laser desorption/ionization mass spectrometry and its application to forensic analysis of drug seizures.

The suitability of atmospheric pressure desorption/ionization on silicon mass spectrometry (AP-DIOS-MS) and matrix-assisted laser desorption ionization mass spectrometry (AP-MALDI-MS) for the identification of amphetamines and fentanyls in forensic samples was studied. With both ionization techniques, the mass spectra recorded showed abundant protonated molecules, and the background did not disturb the analysis. The use of tandem mass spectrometry (MS/MS) allowed unambiguous identification of the amphetamines and fentanyls. AP-DIOS-MS/MS and AP-MALDI-MS/MS were also successfully applied to the identification of authentic compounds from drug seizures. Common diluents and tablet materials did not disturb the analysis and compounds were unequivocally identified. The limits of detection (LODs) for amphetamines and fentanyls with AP-DIOS-MS/MS were 1-3 pmol, indicating excellent sensitivity of the method. The LODs with AP-MALDI-MS/MS were about 5-10 times higher.

Amphetamines↗
PubMed2004

Direct coupling of supercritical fluid extraction to a gas phase atmospheric pressure chemical ionisation source ion trap mass spectrometer for fast extraction and analysis of food components.

Supercritical fluid extraction (SFE) was coupled to a custom-built atmospheric pressure chemical ionization (APCI) source of an ion trap mass spectrometer (ITMS). This method was developed for the monitoring of static or dynamic carbon dioxide extraction of volatile aroma compounds in real time. The gas phase APCI source resulted in simple spectra where the extraction of individual compounds could be monitored. A classical mint extraction was used to demonstrate the possibilities of the method. Influence of cell loading and standard injection possibilities are described. Limit of detection of the system was 0.5 nl or lower for a series of test compounds. Prospect for a fast method for extraction and quantification was raised and discussed.

Atmospheric Pressure↗
PubMed2005

Atmospheric pressure chemical ionisation liquid chromatography/multistage mass spectrometry for assignment of sedimentary bacteriochlorophyll derivatives.

Atmospheric pressure chemical ionisation liquid chromatography/multistage mass spectrometry (APCI-LC/MSn) provides a rapid, on-line method for the assignment of individual bacteriophaeophorbide c and d methyl esters (BPMEs) in complex mixtures. The MS2 spectrum for each component is diagnostic of the type of BPME (c or d), and characteristic losses in MS5 and MS6 permit assignment of the alkyl substituents at positions C-8 and C-12 of the macrocycle. MS5 mass chromatograms permit the deconvolution of coeluting isobaric BPMEs, revealing the true profiles of the individual components. The distributions are different in lake sediments from la Salada de Chiprana (Spain) and Kirisjes Pond (Antarctica), and a novel BPME c with a neo-pentyl substituent has been observed in the Kirisjes Pond sediment.

Bacteriochlorophylls↗