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At least 379 records · Page 21Linked to original sources
PubMed1989

Screening and confirmation of thyreostatics in urine by gas chromatography with nitrogen-phosphorus detection and gas chromatography-mass spectrometry after sample clean-up with a mercurated affinity column.

Methods are described for the screening and confirmation of residues of the thyreostatics thiouracil, methylthiouracil and propylthiouracil in urine samples of cattle at levels down to 25 micrograms/l. After a selective preconcentration of the thiol-containing thyreostatics on a mercurated affinity column, the analytes are derivatized by extractive alkylation and analysed by gas chromatography with nitrogen-phosphorus or mass spectrometric detection.

Animals↗
PubMed2005

Multiresidue analysis of pesticides in soil by gas chromatography with nitrogen-phosphorus detection and gas chromatography mass spectrometry.

A rapid multiresidue method for the simultaneous determination of 25 fungicides and insecticides in soil was developed. Soil samples are extracted by sonication with a water-acetonitrile mixture, and the pesticides are partitioned into dichloromethane. Final determination was made by gas chromatography (GC) with nitrogen-phosphorus detection (NPD). Confirmation analysis of pesticides was carried out by GC-MS in the selected ion monitoring (SIM) mode. The identification of compounds was based on retention time and on comparison of the primary and secondary ions. The average recovery by the GC-NPD method obtained for these compounds varied from 68.5% to 112.1% with a relative standard deviation between 1.8% and 6.2%. The GC-NPD method presents good linearity over the range assayed 50-2000 microg/L, and the detection limit for the pesticides studied varied from 0.1 to 10.4 microg/kg. The proposed method was used to determine pesticide levels in soil samples from experimental greenhouse pepper cultivation.

Chromatography, Gas↗
PubMed2000

Direct thermal desorption-gas chromatography and gas chromatography-mass spectrometry profiling of hop (Humulus lupulus L.) essential oils in support of varietal characterization.

The use of direct thermal desorption-gas chromatography-mass spectrometry (DTD-GC-MS) and DTD-GC-flame ionization detection (DTD-GC-FID) for characterization of hop essential oils is described. Four hop varieties (Nugget, Galena, Willamette, and Cluster) from the Yakima valley (Yakima, WA) 1998 harvest were analyzed by DTD-GC-MS and DTD-GC-FID methodology. Approximately 1 g of hops was needed for the analysis. Hop samples were prepared for GC-MS and/or GC-FID profiling in approximately 20 min. More than 100 volatile compounds have been identified and quantified for each hop variety. The results were found to be in good agreement with conventional steam distillation-extraction (SDE) data. A calibration curve for determination of essential oil content in hops by DTD-GC-FID has been generated. Quantitation of hop oil content by DTD-GC-FID was shown to be in good agreement with conventional SDE data. The recovery of key oil components valuable for varietal identification was demonstrated to be highly reproducible and characteristic of each variety analyzed when DTD-GC-FID was used for analysis.

Chromatography, Gas↗
PubMed2001

Determination of N-nitrosodimethylamine in artificial gastric juice by gas chromatography-mass spectrometry and by gas chromatography-thermal energy analysis.

The thermal energy analyser (TEA) is considered to be the gold standard for the determination of nitrosamines. However, since many laboratories cannot justify the use of such a very specific detection system, alternative detection methods are useful. While standard gas chromatography (GC) detectors lack the selectivity of the TEA detector, mass spectrometry (MS) seems to be the method of choice to combine GC separation with mass selective detection. Moreover, the detection limits of the GC-MS assay in general use are about 4 times lower than those of the GC-TEA assay. A comparison of GC-MS and GC-TEA data on N-nitrosodimethylamine determinations showed a strong correlation between the two assays (R2 = 0.86), demonstrating the exchangeability of these methods.

Carcinogens↗
PubMed1976

Non-polarographic blood gas analysis I. In virtro evaluation of gas chromatograph system.

A new system providing near continuous arterial p02 and pCO2 measurements without requiring blood samples is described. Based on intra-arterial placement of a closed-tipped 2F catheter with gas chromatographic separation and analysis this system appears capable of providing rapid sensitive data with accuracy and precision equivalent to conventional bench analyzers. The initial in vitro experiments are discussed including flow and temperature dependency studies.

Blood Flow Velocity↗
PubMed1976

Serum quinidine concentrations: comparison of fluorescence, gas-chromatographic, and gas-chromatographic/mass-spectrometric methods.

Serum quinidine concentrations were determined in patients on chronic therapeutic doses. Although results were higher by a protein precipitate-fluorescence method as compared to a specific extraction fluorescence method, there was substantial correlation between results by the two methods (r = 0.945, P less than 0.001). We established the specificity of the extraction method by a methylation gas-chromatographic method in which the base peak in the mass spectra of the methylated products of both quinidine and cinchonidine, the internal standard, was monitored. We conclude that the protein precipitate method should be discarded.

Arrhythmias, Cardiac↗
PubMed1979

A methods comparison: clonazepam by gas chromatography-electron capture and gas chromatography-mass spectroscopy.

Clonazepam is an antiepileptic drug for which a number of analytical procedures have been presented, none of which have been subjected to comparison studies. We present two gas chromatographic (GC) methods involving distinct forms of detection for determining plasma or serum drug levels. Both methods involve simple extractions, common GC conditions, and routine data reduction. Both employ nitrazepam as an internal standard, require 1 ml of sample, and have a detection limit of 1 ng/ml. The two methods, GC-electron capture and GC-mass spectroscopy, are precise and accurate. Correlation of the two methods paired sample analysis gave a regression equation of y = 0.988x - 0.14 (n = 30, r = 0.971, p less than 0.001). We suggest that either method is a reasonable alternative for the clinical laboratory with the proper instrumentation.

Benzodiazepinones↗
PubMed1980

Improved cleanup of large lipid samples for electron capture gas chromatographic quantitation and gas chromatographic-mass spectrometric confirmation of organochlorine residues.

A new cleanup method for large lipid samples is described for the analysis of organochlorine traces. The method allows both electron capture gas chromatographic (GC) quantitation of sub-ppb levels and confirmation by GC-mass spectrometry. The lipid is extracted with concentrated sulfuric acid from a 2-5% solution of light petroleum ether. The method has been scaled up without increasing the petroleum volume by the alternate addition of lipids and sulfuric acid. Recovery studies were performed with 11 common organochlorine contaminants spiked in butterfat and in vegetable oils at the ppb level. The method is characterized by low lipid carryover of 0.02% by minimal use of solvent (about 2-3 mL/g lipid), and by its simplicity. A 50-200 g sample can be cleaned up in one day. Five micrograms of incurred p,p'-DDE has been cleaned up from a 50 g butterfat sample and purified by one TLC run. The eluted compound was analyzed by GC-MS and showed one peak (flame photometric detector) with a mass spectrum identical to authentic p,p'-DDE.

Chromatography, Gas↗
PubMedDate not supplied

Analysis of trichothecene mycotoxins in contaminated grains by gas chromatography/matrix isolation/Fourier transform infrared spectroscopy and gas chromatography/mass spectrometry.

Gas chromatography/matrix isolation/Fourier transform infrared (GC/MI/FTIR) spectroscopy and GC/mass spectrometry (MS) were used to confirm the identities of trimethylsilyl (TMS) derivatives of trichothecene mycotoxins in naturally contaminated grains. Infrared spectral bands observed in the fingerprint region were unique for 10 trichothecene standards. Characteristic absorption bands were observed for the ester (near 1750 cm-1) and ketone (near 1700 cm-1) carbonyl stretching vibrations, the acetate CH3 symmetric bend (1370 cm-1), the epoxide ring (1262 cm-1), the trimethylsilyl CH3 in-plane deformation (1253 cm-1), the ester (O)C-O asymmetric stretching vibration (near 1244 cm-1), and several other bands including intense features due to the TMS function. Infrared bands observed under cryogenic matrix isolation conditions were compared with those found at room temperature in a potassium bromide matrix for 5 of these standards. Identities of deoxynivalenol (DON) from barley and mixed feed, nivalenol from wheat and barley, and DON and fusarenon-x from sweet corn were confirmed by comparison of their infrared spectral bands with those of standards. The identity of DON in the same test samples of sweet corn was confirmed further by GC/MS. GC/MS was also used to quantitate the levels of DON (67-455 ppm) in sweet corn test samples.

Chromatography, Gas↗
PubMed1999

Determination of anabolic steroids by gas chromatography/negative-ion chemical ionization mass spectrometry and gas chromatography/negative-ion chemical ionization tandem mass spectrometry with heptafluorobutyric anhydride derivatization.

A gas chromatography/mass spectrometry (GC/MS) method is described which uses negative ion chemical ionization (NCI) and tandem mass spectrometry (MS/MS) for the determination of eight anabolic steroids in human urine. Eight anabolic steroids were derivatized by heptafluorobutyric anhydride (HFBA), and were determined using GC/NCI-MS and GC/NCI-MS/MS. The linear correlation coefficients for calibration in NCI-MS/MS were in the range 0.9880-0.9988. This method of derivatization with HFBA for use with GC/NCI was useful in determinations of 19-norandrosterone, boldenone, 19-noretiocholanolone, 2-methylandrosterone, nandrolone, 1-methyleneandrosterone, 1-methylandrosterone, 4-dihydroboldenone and mesterolone. The detection limits of this procedure were 5-20 ppb at a signal-to-noise (S/N) ratio of 3.

Anabolic Agents↗
PubMed2000

Trace determination of alpha- and beta-endosulfan and three metabolites in human serum by gas chromatography electron capture detection and gas chromatography tandem mass spectrometry.

Endosufan, alpha and beta, and three conversion products, sulphate, ether and lactone, were simultaneously determined in human serum by means of an analytical procedure which combines extraction with organic solvents, clean-up with H(2)SO(4) and by liquid column chromatography, and detection by gas chromatography (GC) using electron capture detection (ECD) and tandem mass spectrometry (MS/MS). The procedure was validated and the values of some merit figures, such as linear range, detection and quantitation limits, accuracy, precision and recovery, obtained with the GC/ECD and the GC/MS/MS methods, were compared. The lower limits of detection in GC/ECD and GC/MS/MS were 0.03 and 0.05 microg I(-1), respectively. The recovery of the pesticides at the 20 microg I(-1) concentration level was 60-65%, with the exception of endosufan alpha. Recovery studies at higher levels (100 and 200 microg I(-1)) were independent of pesticide concentration in serum samples. The application of the proposed analytical methodology to the determination of endosulfans and their metabolites in real samples was tested by analyzing serum samples from a population living in agricultural areas of Almeria (Spain). The results show the advantage of MS/MS over the ECD detector in the analysis of serum samples where matrix interferences can be confused with target pesticides.

Endosulfan↗
PubMed1999

Synchronized gas and partial liquid ventilation in lung-injured animals: improved gas exchange with decreased effort.

We hypothesized that partial liquid ventilation (PLV) with perflubron in spontaneously breathing lung-injured animals would increase respiratory workload compared to animals treated with gas ventilation (GV), and that a fully synchronized mode, assist-control ventilation (AC), would reduce the piglets' effort when compared to intermittent mandatory ventilation (IMV) or synchronized IMV (SIMV) during both GV and PLV. Newborn piglets with saline lavage-induced lung injury were randomized to sequential 30-min periods of IMV --> SIMV --> AC (n = 5), or AC --> SIMV --> IMV (n = 5) during GV followed by PLV. Pulmonary mechanics measurements and an esophageal patient effort index (PEI, defined as the product of the area below baseline of the esophageal pressure-time curve and respiratory rate [RR]) were determined to estimate the patient's nonmechanical work of breathing, using a computer-assisted lung mechanics analyzer. GV to PLV comparisons showed no change in PEI (IMV, 57.8 vs. 49.7; SIMV, 52.3 vs. 46.8; AC, 15.7 vs. 13.7 cm H2O x s/min); intermode comparisons showed significantly decreased PEI in AC vs. IMV and SIMV during GV, and in AC vs. SIMV (AC vs. IMV, P = 0.06) during PLV. AC consistently resulted in the highest minute ventilation, lowest total respiratory rate, most physiologic pH, and least tidal volume variability. These observations suggest that synchronization with AC during GV and PLV may have substantial physiologic benefits.

Animals↗
PubMed1979

Steroids and hypertension. 1--Gas-liquid chromatography and gas chromatography mass spectrometry of 3,15- and 3, 16-dihydroxy-17-oxosteroids.

In order to analyse and quantitate the urinary 16-oxysteroids known or thought to be associated with hypertension, we have established for six 16-oxy-C19 reference steroids the following parameters: elution volume on lipophilic gel columns, gas chromatographic retention data expressed as methylene unit values of trimethylsilyl ether and O-methoxime trimethylsilyl ether derivatives on OV-1 and OV-17 packed columns and on SE-30 capillary column, and mass spectra of these compounds. These reference steroids were: 3 alpha, 16 alpha-dihydroxy-5 alpha-androstan-17-one, 3 alpha, 16 alpha-dihydroxy-5 beta-androstan-17-one, 3 beta, 16 alpha-dihydroxy-5 alpha-androstan-17-one, 3 beta, 16 alpha-dihydroxy-5-androsten-17-one, 3 beta, 16 beta-dihydroxy-5-androsten-17-one, 3 beta, 17 beta-dihydroxy-5-androsten-16-one and 3 alpha, 15 alpha-dihydroxy-5 beta-androstan-17-one. The proposed method was shown to be applicable to the specific analysis of 16-oxy-C19-steroids in biological samples since it achieved the selective isolation of these compounds from other steroids and their quantitative elution in a single fraction. The analysis of the urinary steroids of two patients with arterial hypertension demonstrated an elevated rate of 3 beta, 16 alpha-dihydroxy-5-androsten-17-one.

17-Ketosteroids↗
PubMed1988

Negative ion chemical ionization gas chromatography/mass spectrometry and gas chromatography/tandem mass spectrometry of prostanoid pentafluorobenzyl ester/methoxime/trimethylsilyl ether derivatives.

Negative ion chemical ionization mass spectra of prostaglandin F2 alpha, prostaglandin E2, prostaglandin D2, 6-oxo-prostaglandin F1 alpha, 2,3-dinor-6-oxo-prostaglandin F1 alpha, thromboxane B2, 2,3-dinor-thromboxane B2, and 11-dehydro-thromboxane B2 pentafluorobenzyl ester (PFB)/methoxime/trimethylsilyl ether derivatives are presented. Collisionally activated decomposition mass spectra of the [M-PFB]- ions at collision energies of 8-24 eV and argon collision gas pressures of 1-2m Torr almost show only fragmentation of trimethylsilanol, (CH3)2Si = CHOH, (CH3)2Si = CH2 and methanol whereas, except for carbon dioxide loss, only few low-intensity fragments from the carbon skeleton of the prostanoids are observed.

Esters↗
PubMed1989

Gas chromatographic and gas chromatographic/tandem mass spectrometric characterization of precursors on the sesterterpene pathway for steroid biosynthesis.

An increasing amount of evidence is accumulating to support the proposal that steroidogenesis can occur by a sesterterpene pathway as well as the cholesterol pathway. Key intermediates on the sesterterpene pathway are 23,24-dinor-5-cholen-3 beta-ol (guneribol) and some of its metabolites, e.g. 23,24-dinor-4-cholen-3-one (guneribone). It has been reported that these intermediates are biosynthesized and converted to steroid hormones by a range of endocrine tissues in vitro. Monitoring the pentafluorobenzyloxime derivatives by negative ion chemical ionization mass spectrometry in the electron capture mode provided evidence for the presence of guneribone in extracts of bovine testicular and human adrenal tumour tissue. Complementary evidence was obtained from gas chromatographic/tandem mass spectrometric data generated on a triple-quadrupole instrument by monitoring daughter ions (in the multiple ion detection, MID mode) of the molecular anion of derivatized guneribone in both standards and tissue extracts. The present findings that sesterterpene pathway intermediates are present as endogenous compounds in tissue extracts, together with the previously reported radiochemical data, give further support to the sesterterpene pathway hypothesis.

Adrenal Gland Neoplasms↗
PubMed2006

Prediction of gas chromatographic peak width in capillary columns at different temperatures, carrier gas flows, column lengths, inside diameters and carbon numbers.

Width factor (wf), relative band broadening (br) and retention factor are linearly correlated as ln wf = Inbr + ln k [Chromatographia (2002) 56, 99 -103]. The k and br are thermodynamic and kinetic energy parameters, and expanded to cover volumetric flow of carrier gas, temperature, phase ratio (beta) and carbon number (z). For columns of the same stationary phase and beta value but of different lengths, width at base (wb) can be predicted with the same numerical values of the constants. The average absolute differences between predicted and experimental wb for BP-1 columns of 30, 20 and 10 m are 1.27%, 1.21% and 1.37%, respectively. In predicting Wb of n-alkanes eluted from columns of the same stationary phase but of different ID, only the differences of ln beta are required for adjustment of one of the numerical values. The average absolute differences between Wb(cal) and Wb(exp) values for columns of 0.53, 0.32, 0.22 and 0.15 mm ID are 2.06, 3.67, 3.82 and 3.47%, respectively.

Chromatography, Gas↗
PubMed2001

Simultaneous assessment of cholesterol absorption and synthesis in humans using on-line gas chromatography/ combustion and gas chromatography/pyrolysis/isotope-ratio mass spectrometry.

A number of dietary components and drugs are known to inhibit the absorption of dietary and biliary cholesterol, but at the same time can compensate by increasing cholesterol synthesis. It is, therefore, necessary to have a convenient and accurate method to assess both parameters simultaneously. Hence, we validated such a method in humans using on-line gas chromatography(GC)/combustion and GC/pyrolysis/isotope-ratio mass spectrometry (IRMS). Cholesterol absorption was measured using the ratio of [(13)C]cholesterol (injected intravenously) to [(18)O]cholesterol (administered orally). Simultaneously, cholesterol synthesis was measured using the deuterium incorporation method. Our methodology was applied to 12 mildly hypercholesterolemic men that were given a diet providing 2685 +/- 178 Kcal/day (mean +/- SD) and 255 +/- 8 mg cholesterol per day. Cholesterol fractional synthesis rates ranged from 5.0 to 10.5% pool/day and averaged 7.36% +/- 1.78% pool/day (668 +/- 133 mg/day). Cholesterol absorption ranged from 36.5-79.9% with an average value of 50.8 +/- 15.4%. These values are in agreement with already known data obtained with mildly hypercholesterolemic Caucasian males placed on a diet similar to the one used for this study. However, our combined IRMS method has the advantage over existing methods that it enables simultaneous measurement of cholesterol absorption and synthesis in humans, and is therefore an important research tool for studying the impact of dietary treatments on cholesterol parameters.

Cholesterol↗
PubMed1997

Measurement of nitrite and nitrate in biological fluids by gas chromatography-mass spectrometry and by the Griess assay: problems with the Griess assay--solutions by gas chromatography-mass spectrometry.

Assay methods based on the Griess reaction are frequently used to measure nitrite and nitrate in urine, plasma, and other biological fluids. With minor exceptions, careful attention has not been paid in extending the Griess assay from aqueous solutions to biological fluids, In the present study, parallel measurements of nitrite and nitrate were performed in urine, plasma, and aqueous solutions with a published batch assay based on the Griess reaction and with gas chromatography-mass spectrometry (GC-MS). We report here further interferences by free reduced thiols, proteins, and other plasma constituents in the Griess assay but not in GC-MS. The best correlation (r2 = 0.985) between the Griess assay and GC-MS was observed for aqueous solutions in the absence of thiols. Unlike GC-MS, the Griess assay was not applicable to whole human plasma and urine samples. For the measurement of nitrate in diluted human urine samples, reduction by cadmium was performed both under acidic (pH 2 or 5) and alkaline (pH 8.8) conditions. The mean recovery rate of nitrate from urine samples was quantitative in the GC-MS but amounted to only 30-80% in the Griess assay. Measurement of nitrate in human urine samples (n = 33) resulted in an excellent correlation between two GC-MS techniques (r2 = 0.979) but only in a poor correlation (r2 < 0.64) between the Griess assay and GC-MS. Unlike GC-MS, the batch Griess assay is associated with many problems in measuring nitrate in biological fluids.

Chromatography, High Pressure Liquid↗