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Results for “ATMOSPHERIC PRESSURE”

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PubMed2004

[Spectral diagnosis of dielectric barrier plasma discharge at atmospheric pressure and its application to surface modification of materials].

The spectral lines of air and argon plasma emission at atmospheric pressure were recorded and analyzed. Plasma parameters such as discharge current, discharge gap and electron temperature were measured. The purpose of the study is to control the process of materials' surface modification promptly. The experimental results indicate that a critical discharge gap is an important parameter to improve the quality of materials' surface modification, and spectral diagnosis has been proved to be a workable method by choosing a suitable discharge gap.

English Abstract↗

PubMed2005

[Identification of triacylglycerols in coix oil by high performance liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry].

OBJECTIVE: To identify triacylglycerols in coix oil. METHOD: High performance liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry was used for identification. The experiment was operated under the conditions: spray voltage at 3 000 V, capillary temperature at 250 degrees C, APCI vaporizer temperature at 400 degrees C, and corona current of 4 microA. Sheath gas pressure (high purity liquid nitrogen) was 35 kPa. Mass spectra were obtained over the m/e range of 300 to 900 amu, scan duration of 1s and Q1 peak width at 0.7. The stationary phase was Zorbax Extend C18 column (4.6 mm x 250 mm, 5 microm). The mobile phase: dichloromethane-acetonitrile (35:65), flow rate: 1 mL x min(-1); column temperature: 25 degrees C. RESULT: 12 triacylglycerols were identified by HPLC-MS method. CONCLUSION: The result can be used to identify the components in a fingerprint chromatogram of coix oil and its related injection product.

Chromatography, High Pressure Liquid↗

PubMed2006

Separation of triacylglycerols in a complex lipidic matrix by using comprehensive two-dimensional liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometric detection.

The present investigation describes the employment of a comprehensive 2-D HPLC system, based on the combination of a silver ion and an RP column, for the characterization of the triacylglycerol (TAG) fraction of a very complex lipidic sample: donkey milk fat. The TAGs were grouped on the resulting bidimensional contour plot according to their double bond numbers (aligned along vertical bands) and according to their partition numbers (aligned along horizontal bands). Peak assignment was supported by using atmospheric pressure chemical ionization mass spectrometric (APCI-MS) detection. The combination of the enhanced resolving power of comprehensive multidimensional LC, the formation of ordered 2-D patterns, and APCI-MS detection proved to be an effective tool for the characterization of the complex matrix, enabling the separation and identification of nearly 60 TAGs.

Animals↗

PubMed2005

Quantitative measurement of 3'-oxolutein from human retina by normal-phase high-performance liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry.

3-Hydroxy-beta,epsilon-carotene-3'-one (3'-oxolutein) is the major oxidative metabolite of dietary carotenoids in the retina of the human eye. Elucidating the biochemical mechanism of its formation may provide helpful insight into the pathogenesis of age-related macular degeneration; however, it is found in relatively low quantities that require highly sensitive methods for quantitation from individual retinas. Normal-phase high-performance liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry allowed us to do quantitative analysis of 3'-oxolutein from central and peripheral retinas obtained from individual human donors. The limit of quantification for 3'-oxolutein in human retina at a signal-to-noise ratio of 10 was 6 pg. The precision of the assay yielded a coefficient of variation ranging from 4.7 to 7.4% and accuracies of 106-108%. A statistically significant (R = 0.99, p < or = 0.001) linear working range was achieved between 5 and 7200 pg. The 3'-oxolutein contents from 8-mm punches of the central macula and peripheral retina were found to be 375+/-192 and 191+/-95 pg/tissue, respectively.

Adult↗

PubMed1966

Circulatory responses to simulated gravitational shifts of blood in man induced by exposure of the body below the iliac crests to sub-atmospheric pressure.

1. Exposure of the body from iliac crests to feet of a horizontal subject to a pressure 70 mm Hg below atmospheric causes a displacement of about 10 g of blood/kg total body weight from the upper to the lower part of the body. Much of this blood is returned very rapidly at the end of suction.2. During suction, the changes in the circulation resemble those during a foot-down tilt. After suction, the changes resemble to some extent those following the Valsalva manoeuvre.3. The overshoot of forearm blood flow following suction is caused by variations in the activity of adrenergic vasoconstrictor nerves. The receptors for this reflex have not been identified, but their stimulation depends upon a rapid and large return of blood to the central circulation.

Adrenal Glands↗

PubMed2003

Determination of selenium in human serum by liquid chromatography/electron capture atmospheric pressure chemical ionization mass spectrometry after acid digestion and derivatization using 2,3-diaminonaphthalene.

Analysis of selenium in biological samples is very important and numerous analytical methods for the element have been developed. One of the most convenient and widely used methods for routine determination of serum selenium is a fluorometric method using 2,3-diaminonaphthalene (DAN); however, this method lacks specificity. We observed that 4,5-benzopiazselenol (BPS), a selenium derivative of DAN, is ionized with electron capture in an atmospheric pressure chemical ionization (APCI) interface, and subsequently established a method for determining total human serum selenium by means of liquid chromatography/atmospheric pressure chemical ionization mass spectrometry. All pretreatment procedures were carried out in a single test tube to minimize selenium loss. The recovery of organic or inorganic selenium spiked to human serum was 97-103%. The detection limit of BPS was equivalent to 0.2 ng of selenium and the lower quantitative limit of serum selenium was 10 ng mL(-1). The coefficient of variation of standard concentrations in control serum samples was 4.5%. The purity of the observed peak obtained from serum samples was confirmed using the ion cluster technique.

2-Naphthylamine↗

PubMed2004

Analysis of herbicide Krovar I by liquid chromatography with atmospheric pressure chemical ionization mass spectrometry.

A simple, very efficient method is presented for routine analysis of herbicide Krovar I (active components bromacil and diuron) in water and soil samples. Water samples were extracted by liquid-liquid extraction with dichloromethane (DCM) as extraction solvent. For soil samples two different extraction techniques were compared: microwave-assisted solvent extraction and a shaking technique using a platform shaker. Extracts were analyzed by high performance liquid chromatography using a water:methanol gradient. Liquid chromatography was coupled with atmospheric pressure chemical ionization mass spectrometry (LC-APCI-MS) for quantification of bromacil and diuron. Optimization of the APCI-MS was done by using standards in the flow injection analysis mode (FIA). Method detection limit for liquid samples for bromacil is 0.04 microg L(-1) and for diuron 0.03 microg L(-1). Method detection limit for soil samples is 0.01 microg g(-1) dry weight for both compounds. Results of analysis of field samples of water and soil are also presented.

Atmospheric Pressure↗

PubMed2000

Quantification of free mycophenolic acid by high-performance liquid chromatography-atmospheric pressure chemical ionisation tandem mass spectrometry.

To facilitate the investigation of free mycophenolic acid concentrations we developed a high-performance liquid chromatography tandem mass spectrometry method using indomethacin as an internal standard. Free drug was isolated from plasma samples (500 microl) using ultrafiltration. The analytes were extracted from the ultrafiltrate (200 microl) using C18 solid-phase extraction. Detection was by selected reactant monitoring of mycophenolic acid (m/z 318.9-->190.9) and the internal standard (m/z 356.0-->297.1) with an atmospheric pressure chemical ionisation interface. The total chromatographic analysis time was 12 min. The method was found to be linear over the range investigated, 2.5-200 microg/l (r>0.990, n=6). The relative recovery of the method for the control samples studied (7.5, 40.0 and 150 microg/l) ranged from 95 to 104%. The imprecision of the method, expressed in terms of intra- and inter-day coefficients of variation, was <8 and <9%, respectively. Further, analysis of pooled patient plasma produced an intra-day imprecision of 6.6%. The signal-to-noise ratio at the limit of quantification (2.5 microg/l) was approximately 5:1. The mean absolute recovery (n=6) of mycophenolic acid and the internal standard were 76.0+/-13.5% and 86.0+/-9.1%, respectively. The method reported provides an accurate and precise quantification of free mycophenolic acid over a wide analytical range and thus can be used for routine monitoring and pharmacokinetic studies.

Atmospheric Pressure↗

PubMed2005

Analysis of benzylisoquinoline-type alkaloids by electrospray tandem mass spectrometry and atmospheric pressure photoionization.

Benzylisoquinoline alkaloids found in the Papaveraceae family play a major role in pharmaceutical biology. This is the first systematic study dealing with electrospray tandem mass spectrometry (ESI-MS/MS) of all benzylisoquinolines found as biogenetic precursors of morphinan alkaloids. Tandem mass spectral data are presented for norlaudanosoline, laudanosoline, 4'-O-methyl-norlaudanosoline, 6-O-methyl-norlaudanosoline, norcoclaurine, coclaurine, N-methylcoclaurine, N-methyl-3'-hydroxycoclaurine, N-methyl-3'-O-methylcoclaurine, norreticuline and reticuline. This study compares results obtained using an ion trap mass spectrometer with those obtained using a triple quadrupole one. The results highlight the differences of the tandem-in-time versus the tandem-in-space principle, often hampering the development of ESI-MS/MS libraries. Additionally, the use of the atmospheric pressure photoionisation technique for the analysis of such substances is discussed.

Alkaloids↗

PubMed1999

Determination of the antifouling agent zinc pyrithione in water samples by copper chelate formation and high-performance liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry.

Zinc pyrithione has recently been incorporated into antifouling paints as a booster biocide, which is slowly released into the water as the paint ages. In order to determine concentrations of zinc pyrithione (ZPT) in aqueous samples, a liquid chromatographic method has been developed. Since ZPT interacts with certain reversed-phase packing materials or stainless steel components of the HPLC system, the method uses transchelation of the ZPT into the stable copper(II) complex before analysis by liquid chromatography coupled to atmospheric pressure chemical ionisation mass spectrometry. ZPT was extracted as copper pyrithione using dichloromethane with adequate recovery (77% +/- 17%, n = 6) from 2-l water samples. The limit of detection was calculated to be 20 ng/l, using selected ion monitoring. The analysis of samples collected from various UK marinas showed no detectable concentrations to be present, whilst a laboratory-based study confirmed that this is probably due to the rapid photodegradation of ZPT in seawater.

Anti-Infective Agents↗

PubMed2002

Analysis of polynitrophenols and hexyl by liquid chromatography-mass spectrometry using atmospheric pressure ionisation methods and a volatile ion-pairing reagent.

An LC-MS method for the determination of picric acid (2,4,6-trinitrophenol), its reductive transformation products picramic acid (2-amino-4,6-dinitrophenol) and iso-picramic acid (4-amino-2,6-dinitrophenol) and hexyl (2,2',4,4',6,6'-hexanitrodiphenylamine) has been developed. The analytes were separated using ion-pairing chromatography with a volatile ion-pairing reagent suitable for subsequent MS detection. The performance of an atmospheric pressure chemical ionisation (APCI) and an electrospray ionisation (ESI) interface was compared. ESI-MS is more sensitive for the analytes, especially for hexyl and picric acid, APCI-MS delivered more fragments necessary for unequivocal identification. With LC-ESI-MS limits of detection using single ion monitoring (SIM) mode are 4 ng (iso-picramic acid), 800 pg (picramic acid), 400 pg (picric acid) and 80 pg (hexyl). For quantification, 15N-picric acid was used as an internal standard. Using this new method, the degradation of picric acid in soil was monitored in a laboratory study. Furthermore, the presence of picramic acid was for the first time verified in soil samples from a former ammunition plant.

Atmospheric Pressure↗

PubMed2004

Determination of tamsulosin in dog plasma by liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry.

A rapid, sensitive and accurate liquid chromatographic-tandem mass spectrometric method is described for the determination of tamsulosin in dog plasma. Tamsulosin was extracted from plasma using a mixture of hexane-ethyl acetate (2:1, v/v) and separated on a C18 column interfaced with a triple quadrupole tandem mass spectrometer. The mobile phase consisting of a mixture of methanol, water and formic acid (80:20:1, v/v/v) was delivered at a flow rate of 0.5 ml/min. Atmospheric pressure chemical ionization (APCI) source was operated in positive ion mode. Selected reaction monitoring (SRM) mode using the transitions of m/z 409-->m/z 228 and m/z 256-->m/z 166.9 were used to quantify tamsulosin and the internal standard, respectively. The linearity was obtained over the concentration range of 0.1-50.0 ng/ml for tamsulosin and the lower limit of quantitation was 0.1 ng/ml. For each level of QC samples, inter- and intra-run precision was less than 5.0 and 4.0% (relative standard deviation (R.S.D.)), respectively, and accuracy was within +/-0.3% (relative error (R.E.)). This method was successfully applied to pharmacokinetic study of a tamsulosin formulation product after oral administration to beagle dogs.

Administration, Oral↗

PubMed2000

Identification and quantification of flavonoids in human urine samples by column-switching liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry.

A rapid and sensitive high-performance liquid chromatographic mass spectrometric (HPLC-MS) method is described for the determination and quantification of 12 dietary flavonoid glycosides and aglycons in human urine samples. Chromatographic separation of the analytes of interest was achieved by column-switching, using the first column (a Zorbax 300SB C-3 column) for sample cleanup and eluting the heart-cut flavonoid fraction onto the second column (a Zorbax SB C-18 column) for separation and detection by ultraviolet and atmospheric pressure chemical ionization MS using single ion monitoring in negative mode. The fragmentor voltage was optimized with regard to maximum abundance of the molecular ion and qualifier ions of the analytes. Calibration graphs were prepared for urine, and good linearity was achieved over a dynamic range of 2.5-1000 ng/mL. The inter- and intraassay coefficients of variation for the analysis of the 12 different flavonoids in quality control urine samples were 12.3% on average (range 11.0-13.7%, n = 24, reproducibility) and the repeatability of the assay were 5.0% (mean, range 0.1-14.8%, n = 12). A subset of 10 urine samples from a human dietary intervention study with high and low flavonoid content was analyzed, and the results are reported.

Atmospheric Pressure↗

PubMed1999

Use of an ion-pairing reagent for high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry determination of anionic anticoagulant rodenticides in body fluids.

The on-line combination of high-performance liquid chromatography with mass spectrometry (HPLC-MS) has become a powerful tool for trace analysis thanks to the developments in interface techniques. However, non-volatile salts such as ion-pairing reagents are considered to be incompatible with HPLC-MS systems; they cause drops in analyte signals because of contamination of mass analyzers and also because of blocking of the capillary transferring ions from atmospheric pressure to the vacuum manifold. In this work, a new type of ion-pairing reagent, di-n-butylammonium acetate (DBA), was evaluated for use in HPLC-MS. DBA did not cause these problems to HPLC-MS systems; a possible explanation might be that DBA decomposed to volatile compounds under APCI conditions. In addition, DBA was very useful for obtaining sharp peaks, which resulted in high sensitivity. With this ion-pairing reagent, we developed a procedure for the measurement of five (including internal standard) anticoagulant rodenticides in whole blood and urine samples by SIM detection of [M-H]- ions. Calibration range, recoveries and precision of the method were examined; detection limits as low as 1-5 ng/ml blood sample or 0.5-2.5 ng/ml urine sample were achieved.

Animals↗

PubMedDate not supplied

Analysis of the enantiomers of VX using normal-phase chiral liquid chromatography with atmospheric pressure chemical ionization-mass spectrometry.

The chemical warfare nerve agent O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothioate (VX) is a mixture of two enantiomers resulting from the chiral center at the phosphorus atom. Significant differences exist in the reported toxicity and acetylcholinesterase inhibition rates of the two enantiomers. This makes the ability to distinguish between them desirable for either toxicological studies or the development of antidotal therapies. Using a Chiralcel OD-H column with normal-phase liquid chromatography, the enantiomers were baseline resolved in less than 7 min. Atmospheric pressure chemical ionization was utilized as the interface between a liquid chromatograph and mass spectrometer. The mass spectra of the two enantiomers were virtually identical. The protonated molecule was readily observed at m/z 268. VX was incubated with human plasma for 13 min, followed by hexane extraction. The areas of the first and second eluting VX enantiomers decreased by approximately 40% and 6%, respectively, when compared with VX-spiked plasma samples that were not allowed an incubation phase. Currently, research by others has been directed towards the identification, isolation, and possible modification of enzymes capable of hydrolyzing VX. The method presented here provides an analytical tool capable of monitoring the stereospecificity of enzymes that react with VX.

Atmospheric Pressure↗

PubMed1996

Determination of epimers 22R and 22S of budesonide in human plasma by high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.

A highly sensitive and selective method has been developed for the simultaneous quantification of 22R- and 22S-epimers of budesonide in human plasma. The drug was isolated from human plasma using C18 solid-phase extraction cartridges and was acetylated with a mixture of 12.5% acetic anhydride and 12.5% triethylamine in acetonitrile to form the 21-acetyl derivatives. Deuterium-labelled budesonide was synthesized and determined to have an isotopic purity > 99%. This was used as the internal standard. Epimers were quantified by automated liquid chromatography-atmospheric pressure chemical ionization mass spectrometry, operating in selected ion mode at m/z 473.2 and m/z 476.2. Linear responses were observed for both epimers over the range 0.25 to 10.0 ng/ml. The average recoveries of 22R- and 22S-epimers of budesonide from human plasma were 87.4% and 87.0%, respectively. The lower limit of quantification for each epimer was 0.25 ng/ml, corresponding to 50.0 pg of analyte on column. Within- and between-day coefficients of variation were 8.6% and 4.0%, respectively.

Administration, Topical↗

PubMed2005

Integration of ion-exchange chromatography fractionation with reversed-phase liquid chromatography-atmospheric pressure chemical ionization mass spectrometer and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for isolation and identification of compounds in Psoralea corylifolia.

An approach for the separation and identification of components in a traditional Chinese medicine Psoralea corylifolia was developed. Ion-exchange chromatography (IEC) was applied for the fractionation of P. corylifolia extract, and then followed by concentration of all the fractions with rotary vacuum evaporator. Each of the enriched fractions was then further separated on an ODS column with detection of UV absorbance and atmospheric pressure chemical ionization mass spectrometer (APCI/MS), respectively, and also analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS) with matrix of oxidized carbon nanotubes. Totally more than 188 components in P. corylifolia extract were detected with this integrated approach, and 12 of them were preliminary identified according to their UV spectra and mass spectra performed by APCI/MS and MALDI-TOF/MS. The obtained analytical results not only demonstrated the powerful resolution of integration IEC fractionation with reversed-phase liquid chromatography (RPLC)-APCI/MS and MALDI-TOF/MS for analysis of compounds in a complex sample, but also exhibited the superiority of APCI/MS and MALDI-TOF/MS for identification of low-mass compounds, such as for study of traditional Chinese medicines (TCMs) and metabolome.

Atmospheric Pressure↗

PubMed2004

Analysis of 21-deoxycortisol, a marker of congenital adrenal hyperplasia, in blood by atmospheric pressure chemical ionization and electrospray ionization using multiple reaction monitoring.

Congenital adrenal hyperplasia (CAH) is an autosomal recessive disorder mainly caused by 21-hydroxylase deficit (21-OHD). Deletions or mutations of the CYP21 gene induce the impairment of glucocorticoid and mineralcorticoid synthesis. 17-Hydroxyprogesterone (17-OHP) is the hormonal marker in patients, but not in the heterozygous subjects. Excess 17-OHP is hydroxylated into 21-deoxycortisol (21-DF), and therefore 21-DF can be used as a specific marker for diagnosis of heterozygous individuals. We report an analytical method for analysis of 21-DF in blood samples using electrospray (ESI) and atmospheric pressure chemical ionization (APCI), showing that ESI is very sensitive for the analysis of this marker molecule. The multiple reaction monitoring (MRM) approach was used to increase the specificity and the sensitivity of the method.

Adrenal Hyperplasia, Congenital↗