Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “GAS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 199 records · Page 11Linked to original sources
PubMed1993

Simultaneous analysis of 25 pesticides in crops using gas chromatography and their identification by gas chromatography-mass spectrometry.

The simultaneous analysis of 25 pesticides in soy beans and rices was performed by gas chromatography with dual electron-capture detection and nitrogen-phosphorus detection. The pesticides were extracted from the samples with solvent and the Bio-Beads S-X3 clean-up procedure was used. Recovery studies were performed at the 1-ppm level of pesticides added to each crop. Their recoveries ranged between 83 and 105% with coefficient of variations of 0.5-8.2%. The gas chromatographic properties of the 25 pesticides were also investigated. Conformation analysis was achieved by the retention time and characteristic fragment ions using the technique of gas chromatography-mass spectrometry-selected-ion monitoring.

Chromatography, Gas↗
PubMed1991

Gas chromatography-mass spectrometry in the investigation of on-column dehydration of steroid hormones during gas-liquid chromatography.

Some underivatized steroids when injected onto conventional packed columns for gas-liquid chromatography underwent varying degrees of dehydration. This problem was traced to the presence of small pieces of broken glass on the top of the column at the point of injection. This observation provoked an examination of the effect of pre-column dehydration on a number of different types of steroids. Powdered aluminium was placed in the injection liner of a Hewlett-Packard gas chromatograph fitted with an HP1 capillary column connected to a mass selective detector, and injections were made using a new high temperature septumless injection system at temperatures between 200 and 400 degrees C. 5 alpha-androstan-3 alpha-ol, a simple monofunctional C19 steroid chosen as a model to establish optimum conditions, underwent dehydration at injection temperatures greater than 250 degrees C and the product reached a maximum at 400 degrees C when no unchanged steroid was present. Monohydroxylated androgens and oestrogens underwent dehydration at 400 degrees C producing products whose mass spectra indicated they were monenes, although the position of the double bond could not be assigned. Polyfunctional androgens and oestrogens and corticosteroids underwent complex changes producing a number of products some of whose structures could not be determined. The dehydration products had the advantage that they had relatively intense high mass ions and for suitable steroids this might provide enhanced sensitivity of detection during mass fragmentography. In such cases dehydration was reproducible and straight line standard curves were obtained. C27 and C28 secosteroids (vitamins D2 and D3) and some of their metabolites (e.g. 25-hydroxyvitamin D) underwent efficient dehydration, again producing products with intense molecular ions. In the case of 24,25-dihydroxyvitamin D3 and 25,26-dihydroxyvitamin D3, dehydration produced different products which were easily resolved in the chromatographic system used. Dehydration of vitamin D metabolites eliminates the need for derivatization and gives enhanced sensitivity of measurement by gas chromatography-mass spectrometry.

Androgens↗
PubMed2006

Solid-phase extraction-gas chromatography and solid-phase extraction-gas chromatography-mass spectrometry determination of corrosion inhibiting long-chain primary alkyl amines in chemical treatment of boiler water in water-steam systems of power plants.

Gas chromatography with simultaneous flame-ionization detection (FID) and a nitrogen-phosphorus detection (NPD) as well as gas chromatography-mass spectrometry (GC/MS) has been used to characterize long-chain primary alkyl amines after derivatization with trifluoroacetic anhydride (TFAA). Electron impact ionization- (EI) and negative chemical ionization (NCI) mass spectra of trifluoroacetylated derivatives of the identified tert-octadecylamines are presented for the first time. The corrosion inhibiting alkyl amines were applied in a water-steam circuit of energy systems in the power industry. Solid-phase extraction (SPE) with octadecyl bonded silica (C18) sorbents followed by gas chromatography were used for quantification of the investigated tert-octadecylamines in boiler water, superheated steam and condensate samples from the power plant. The estimated values were: 89 microg l(-1)(n = 5, RSD = 7.8%), 45 microg l(-1) (n = 5, RSD = 5.4%) and 37 microg l(-1)(n = 5, RSD = 2.3%), respectively.

Amines↗
PubMed2000

Determination of nitrate in blood by gas chromatography and gas chromatography-mass spectrometry.

We devised a sensitive and simple method for determining nitrate in whole blood, using an extractive alkylation technique. Nitrate in whole blood was reduced to nitrite by hydrazine sulfate in the presence of Cu2+ and Zn2+ as catalysts, and alkylated with pentafluorobenzyl bromide using tetradecyldimethylbenzylammonium chloride as the phase-transfer catalyst. The obtained derivative was analyzed qualitatively by gas chromatography-mass spectrometry and quantitatively by gas chromatography with electron-capture detection. The detection limit of nitrate in whole blood was 0.01 mM. The calibration curve was linear over the concentration range from 0.02 to 1.0 mM for nitrate in whole blood. The accuracy and precision of the method were evaluated and the relative standard deviations were found to be within 10%. Using this method, the blood nitrate levels of two victims who committed suicide by inhaling automobile exhaust gas were determined.

Alkylation↗
PubMed1991

Metabolic gas exchange during aortocoronary bypass surgery using a double pump system and mechanical ventilation. A comparison between indirect calorimetry and invasive blood gas measurements using Fick's principle.

Oxygen uptake and carbon dioxide excretion during aorto-coronary bypass surgery were studied in seven patients by indirect calorimetry and compared to blood-gas based measurements. Medium-high dose fentanyl, droperidol and midazolam were used for maintaining anaesthesia. During the period of extracorporeal circulation no external oxygenator was used. Circulation was maintained by two pumps by-passing the left and right heart respectively and the patient's lungs were ventilated with O2/N2 using a Servo 900C ventilator. For indirect calorimetric measurements gas concentrations were analysed by Beckman instruments and gas volumes were measured by the Servo 900C ventilator. Oxygen uptake and carbon dioxide excretion decreased by 31% and 39%, respectively. For invasive measurements during extracorporeal circulation, arterial and venous blood gases and pump flow were used. Using pump flow instead of cardiac output when calculating oxygen uptake circumvented errors in thermodilution measurements. There was a good correlation (r = 0.88) between the invasive and the indirect calorimetric measurements. Further, there was a good correlation between naso-pharyngeal temperature and indirect calorimetric measurements of oxygen uptake (r = 0.87).

Blood Gas Analysis↗
PubMed2006

Determination of the concentration of diallyl trisulfide in rat whole blood using gas chromatography with electron-capture detection and identification of its major metabolite with gas chromatography mass spectrometry.

A simple, rapid, and sensitive procedure has been developed using gas chromatography with electron-capture detection to measure diallyl trisulfide levels in rat blood. Blood samples were acidified, and the analyte was extracted with hexane, and then degradation was stopped with acetonitrile before gas chromatographic separation. Two calibration curves were linear over the range of 10-500 ng/ml and 0.2-20 microg/ml, with typical r values of 0.9986 and 0.9993, respectively. The structure of its major metabolite was confirmed using combined gas chromatography-mass spectrometry. The limit of detection was less than 10 ng/ml, and the assay was highly reproducible, giving peaks with excellent chromatographic properties. The method is suitable for pharmacokinetic and therapeutic purposes.

Allyl Compounds↗
PubMedDate not supplied

Studies on gas tension in the normal middle ear. Gas chromatographic analysis and a new sampling technique.

In studying mechanisms regulating the middle ear pressure it is essential to know the gas compositions of the middle ear. We have constructed a device which made it possible to sample middle ear gas without creating a negative pressure, thus eliminating the risk of admixture of atmospheric air. The samples were analysed by gas chromatography. In 26 normal subjects we found relatively stable values of carbon dioxide (median 52 mmHg, range 31-69 mmHg) and nitrogen (median 605 mmHg, range 563-627 mmHg). The values of oxygen were more fluctuating (median 54 mmHg, range 23-111 mmHg). In 10 of the subjects, arterial gases were determined simultaneously. No correlation could be shown between middle ear and arterial oxygen and carbon dioxide tensions. This investigation provides evidence contradicting the classical theory of a high negative middle ear pressure in Eustachian tube closure. We found strong indications that the Eustachian tube plays an active role in regulating the pressure in the normal middle ear, but variations in blood flow through the middle ear capillaries may also be an important regulating factor.

Adult↗
PubMed1991

Analysis of ethyl alcohol concentration in blood using gas chromatography equipped with blood gas sampler.

We compared the method using blood gas sampler with head space method for analysis of ethyl alcohol concentration in blood. The introduction mechanism of sample into gas chromatography is similar to pyrolyzer, but this apparatus is less complex than pyrolyzer. The calibration curve analyzed using BGS-1A became linear from 0.0 mg/ml and 6.0 mg/ml ethyl alcohol concentration as same as head space method. But, the linearity was worse than head space method. The linearity at low concentration of ethyl alcohol was better than at high concentration. The slopes of calibration curve of BGS-1A method and head space method were 3.5 and 4.05, respectively. These values were very close. After one assay, sample was reinjected without changing the new filter paper of glass sample tube of BGS-1A. No sample accumulation was observed. Ethyl alcohol in only 0.5 microliter of blood was detectable, and this volume was considerably smaller than head space method. The quantitative analysis of ethyl alcohol in blood using blood gas sampler BGS-1A, was usable. And, this method was more convenient than the head space method. Because, the sample volume become smaller and the additional instruments (for instance, vials, air-tight syringe, incubator for heating vials and oven for heating syringe) were not needed. And the heating time for the equilibration of samples between air phase and liquid phase was not needed.

Blood Gas Analysis↗
PubMed2005

Analysis of the 13C natural abundance of CO2 gas from sparkling drinks by gas chromatography/combustion/isotope ratio mass spectrometry.

A simple and rapid method to measure naturally occurring delta(13)C values of headspace CO(2) of sparkling drinks has been set up, using direct injections on a gas chromatograph coupled to an isotope ratio mass spectrometer, through a combustion interface (GC/C/IRMS). We tested the method on CO(2) gas from several origins. No significant isotopic fractionation was observed nor influences by secondary compounds eventually present in the gas phase. Standard deviation for these measurements was found to be <0.1 per thousand.

Carbon Dioxide↗
PubMed2005

Subcutaneous gas tensions closely track ileal mucosal gas tensions in a model of endotoxaemia without anaerobism.

OBJECTIVE: Few comparative data exist on the responses of the subcutaneous and splanchnic circulations to evolving endotoxic shock. We therefore compared continuous subcutaneous pO(2) (pO(2sc)) and pCO(2) (pCO(2sc)) with simultaneous continuous gut luminal pCO(2) (pCO(2gi)) in an animal model of endotoxaemia and examined whether changes in gas tensions track tissue energy charge (EC). DESIGN: Prospective observational study. SUBJECTS: Fourteen anaesthetized rats, 7 controls and 7 experimental. INTERVENTIONS: Controls were injected with saline, the experimental group with 20 mg/kg Klebsiella endotoxin. pCO(2sc), pO(2sc), and pCO(2gi) were measured continuously. Plasma lactate concentrations were measured at defined periods during the study. After 2 h ileal segments were snap frozen and assayed for tissue EC. MEASUREMENTS AND RESULTS: Endotoxaemia resulted in a significant decrease in mean arterial blood pressure (132+/-9 to 71+/-20 mmHg) and pO(2sc) (71+/-23 to 33+/-22 torr) and a significant increase in pCO(2gi) (58+/-10 to 90+/-20 torr) and pCO(2sc) (56+/-6 to 81+/-25 torr). During endotoxaemia pCO(2gi) was directly correlated with pCO(2sc) (R (2)=0.5) and inversely correlated with pO(2sc) (R (2)=0.63). Plasma lactate concentrations were significantly elevated from baseline in the endotoxin limb. The mean EC was not significantly different in the two groups. CONCLUSIONS: Both subcutaneous tissue gas tensions and intestinal luminal carbon dioxide tensions are rapidly responsive during evolving hypodynamic endotoxic shock. Alterations in tissue gas tensions were not associated with dysoxia.

Animals↗
PubMed1991

Alignment of ventilation and gas fraction for breath-by-breath respiratory gas exchange calculations in exercise.

The effects of correct alignment of the ventilation and fractional gas concentration during breath-by-breath calculation of oxygen uptake (VO2) have been examined during exercise in four subjects, at each of 50, 100, 150, and 200 W. Data were analyzed using lagtimes in the range of 200 to 400 msec to align ventilation with gas fraction. VO2 was markedly affected by lagtime. Calculated values of VO2 at 200 W ranged from 1953 +/- 55 (mean +/- SEM), to 2583 +/- 29, to 2843 +/- 28 ml.min-1 with lagtimes of 200, 310, and 400 msec, respectively. Mean values from a mixing box system did not differ significantly from the mean of the breath-by-breath data collection with a lagtime of 310 msec. Additional computations have shown that temperature correction can markedly affect calculated ventilatory volumes and N2 balance. VO2 was not changed because of the compensation from the calculated effects of changes in lung gas stores.

Algorithms↗
PubMed1985

Mutagenic/carcinogenic agents in indoor pollutants; the dinitropyrenes generated by kerosene heaters and fuel gas and liquefied petroleum gas burners.

Incomplete combustion of kerosene heater, and fuel gas and liquefied petroleum gas-burner emissions produces indoor pollutants that may be carcinogenic. The incomplete-combustion products from each type of appliance were therefore collected by adsorption on about 3 g of XAD-2 resin, and were extracted with benzene-methanol as a solvent for determination and identification of mutagens in the Salmonella-microsome test system. Benzene-methanol extracts of the particulates generated by a heater and two burners showed extreme mutagenicity for strains TA97 and TA98 without S9 mix. Based on the results of analysis, a combination of high performance liquid chromatography (h.p.l.c.) and gas chromatography (GC), about 40-80% of the direct-acting mutagenicity in each crude extract showed the same h.p.l.c. and GC retention times as dinitropyrenes (1,3-, 1,6- and 1,8-isomers), and 1-nitropyrene. Moreover, other nitroarenes, 2-nitrofluorene, 1,5- and 1,8-dinitronaphthalene, and 4,4'-dinitrobiphenyl, were detectable in almost all samples, but their contribution to the mutagenicity of each extract was very low. Kerosene heaters were found to generate small amounts (0.2 ng/h) of dinitropyrenes, which are potential mutagens/carcinogens, only after 1 h of operation.

Air Pollutants↗
PubMed2004

Effects of acute temperature changes on aerial and aquatic gas exchange, pulmonary ventilation and blood gas status in the South American lungfish, Lepidosiren paradoxa.

Lungfish (Dipnoi) are probably sister group relative to all land vertebrates (Tetrapoda). The South American lungfish, Lepidosiren paradoxa, depends markedly on pulmonary gas exchange. In this context, we report on temperature effects on aquatic and pulmonary respiration, ventilation and blood gases at 15, 25 and 35 degrees C. Lung ventilation increased from 0.5 (15 degrees C) to 8.1 ml BTPS kg(-1) min(-1) (35 degrees C), while pulmonary O(2)-uptake increased from 0.06 (15 degrees C) to 0.73 ml STPD kg(-1) min(-1) (35 degrees C). Meanwhile aquatic O(2)-uptake remained about the same ( approximately 0.01 ml STPD kg(-1) min(-1)) at all temperatures. Concomitantly, the pulmonary gas exchange ratio (R(E)) rose from 0.11 (15 degrees C) to 0.62 (35 degrees C), because a larger fraction of total CO(2) output became eliminated by the lung. Accordingly, PaCO(2) rose from 13 (15 degrees C) to 37 mm Hg (35 degrees C), leading to a significant decrease of pHa at higher temperature (pHa=7.58-15 degrees C; 7.33-35 degrees C). The acid-base status of L. paradoxa was characterized by a generally low pH (7.4-7.5), high bicarbonate level (20-25 mM) and PaO(2) ( approximately 80 mm Hg). The increased dependence on the lung at higher temperature parallels data for amphibians. Further, the effects of bimodal gas exchange on temperature-dependent acid-base regulation closely resemble those of anuran amphibians.

Animals↗
PubMed2004

Determination of gas-liquid partition coefficients by gas chromatography.

This review covers theoretical principles and experimental procedures for the determination of gas-liquid partition coefficients, KL, by gas chromatography. In order to precisely define the relationship between KL, retention time and experimental parameters, the retention theory, both for ideal and for imperfect gas phase, is expounded. The most important sources of systematic error, as peak asymmetry, mixed retention mechanisms, column hold-up time and stationary phase mass determination, are discussed. Although the review is focussed on packed columns, comparison to capillary columns is discussed in those aspects in which these last show advantages.

Chemical Phenomena↗
PubMed2005

Harmonisation of coupled calibration curves to reduce correlated effects in the analysis of natural gas by gas chromatography.

Quantitative analysis of natural gas depends on the calibration of a gas chromatograph with certified gas mixtures and the determination of a response relationship for each species by regression analysis. The uncertainty in this calibration is dominated by variations in the amount of the sample used for each analysis that are strongly correlated for all species measured in the same run. The "harmonisation" method described here minimises the influence of these correlations on the calculated calibration curves and leads to a reduction in the root-mean-square residual deviations from the fitted curve of a factor between 2 and 5. Consequently, it removes the requirement for each run in the calibration procedure to be carried out under the same external conditions, and opens the possibility that new data, measured under different environmental or instrumental conditions, can be appended to an existing calibration database.

Calibration↗
PubMed2006

The combination of gas chromatography-olfactometry and multidimensional gas chromatography for the characterisation of essential oils.

A research area of great interest to the flavour industry is the analysis of odour active compounds in essential oils. In this paper, a methodology is presented for the identification of character-impact odorants in essential oil samples using (a) gas chromatography-olfactometry (GC-O); (b) comprehensive two-dimensional gas chromatography (GC x GC) combined to time-of-flight mass spectrometry (TOFMS) and (c) heart-cut multidimensional gas chromatography-olfactometry (MDGC-O). The specific advantages and limitations of each technique are discussed. The advantage of combining these techniques in a strategy to identify character-impact odorants is demonstrated using examples from coriander leaf (Coriandrum sativum) and hop (Humulus lupulus) essential oils. In particular, resolution of co-eluting regions of compounds and evaluation of their individual odour activity is discussed. In coriander leaf, only E-2-dodecenal was found to contribute to a co-eluting odour region, E-2-dodecen-1-ol and 1-dodecanol being present below detection threshold. Using MDGC on a hop essential oil sample, eight significant peaks were resolved from an 18 s heart-cut where a potent odorant was perceived during GC-O.

Chromatography, Gas↗
PubMed1997

Gas chromatographic-mass spectrometry and gas chromatographic-Fourier transform infrared spectroscopy assay for the simultaneous identification of fentanyl metabolites.

Fentanyl, a synthetic opioid, undergoes important biotransformation to several metabolites. A gas chromatographic-mass spectrometric assay was applied for the simultaneous analysis of fentanyl and its major metabolites in biological samples. The identification of different metabolites was performed by gas chromatography-mass spectrometry (electronic impact and chemical ionisation modes) and gas chromatography-Fourier transform infrared spectroscopy. In the present study, rat and human microsomes incubation mixtures and human urines were analysed. In vitro formation of already known fentanyl metabolites was confirmed. The presence of metabolites not previously detected in human urine is described.

Analgesics, Opioid↗
PubMed1987

[Analysis of atmospheric pollutants with coupled gas chromatography-atomic absorption or thermodesorption-gas chromatography].

We have perfected a specific and original analytical method suitable for organic and inorganic compounds using sampled run-off water collected nearby a filling station. The dissolved lead species are volatilized by substituting the inorganic ligands with hydrogen, using sodium-borohydride in a suitable reaction medium (H2O2, KOH). The volatile lead hydrides are then trapped on a gas chromatographic column filled with Chromosorb W impregnated with 2% of OV 275 and immersed in liquid nitrogen. After desorption, the products are analysed by atomic absorption spectroscopy. We have carried out the analysis of aldehydes mixtures, sampled from a smog chamber. They are trapped, at room temperature, in a glass column filled with Tenax. These pollutants are then heated at 250 degrees C under a flow of nitrogen, and trapped again in a melted silica capillary column at -110 degrees C. This trapping being over, the column is drastically heated at 200 degrees C, which drives the products into the capillary column of a gas-chromatograph apparatus. This method has also enabled us to carry out a direct analysis of these pollutants sorbed on particles which have been placed into the glass column. this thermodesorption-gas chromatography system, coupled with a mass-spectrometry apparatus, allows us to identify and analyse most atmospheric pollutants.

Air Pollutants↗