High-precision Gas Chromatography Research Articles

Turnover of brain DHA in mice is accurately determined by tracer-free natural abundance carbon isotope ratio analysis

The brain is highly enriched in the long-chain omega-3 (n-3) PUFA DHA. Due to the limited capacity for local DHA synthesis in the brain, it relies on a continual supply from the circulation to replenish metabolized DHA. Previous studies investigating brain DHA turnover and metabolism have relied on isotope tracers to determine brain fatty acid kinetics; however, this approach is cumbersome and costly. We applied natural abundance carbon isotope ratio analysis via high-precision gas chromatography combustion isotope ratio mass spectrometry, without the use of labeled tracers, to determine the half-life of brain DHA in mice following a dietary switch experiment. Mice fed diets containing either α-linolenic acid (ALA) or DHA as the sole dietary n-3 PUFA were switched onto diets containing ALA, DHA, or ALA + DHA at 6 weeks of age, while control mice were maintained on their respective background diet. We measured brain DHA carbon isotope ratios (reported as δ13CDHA signatures) over a 168-day time course. Brain δ13CDHA signatures of control mice maintained on background diets over the time course were stable (P > 0.05). Brain δ13CDHA signatures of mice switched to the DHA or ALA + DHA diet from the ALA diet changed over time, yielding brain incorporation half-lives of 40 and 34 days, respectively. These half-lives determined by natural abundance carbon isotope ratio analysis were consistent with estimates from kinetic isotope tracer studies. Our results demonstrate the feasibility of natural abundance carbon isotope ratio analysis in the study of fatty acid metabolism without the use of isotopically labeled fatty acid tracers.

Conjunctive use of in situ gas sampling and chromatography with geospatial analysis to estimate greenhouse gas emissions of a large Amazonian hydroelectric reservoir

Hydroelectric power reservoirs are considered potential contributors to the greenhouse effect in the atmosphere through the emittance of methane and carbon dioxide. We combined in situ sampling and gas chromatography with geostatistical and remote sensing approaches to estimate greenhouse gas (GHG) emissions of a large hydropower reservoir. We used remote sensing data to estimate the water surface and geospatial interpolation to calculate total emissions as a function of reservoir surface area. The CH4 and CO2 gas concentrations were linearly correlated to sampling time, confirming the adequacy of the in situ sampling method to measure GHG diffusive fluxes from reservoir water surfaces. The combination of high purity (99.99%) ISO-norm gas standards with a gas chromatograph, enabled us to achieve low measurement detection limits of 0.16 and 0.60 μmol mol−1, respectively, for CH4 (using a flame ionization or FID detector) and CO2 (using a thermal conductivity or TCD detector). Our results show that CO2 emissions are significantly (an order of 5.102–103) higher than those of CH4 in both the spatial and temporal domain for this reservoir. The total diffusive GHG emissions over a year (June 2011 to May 2012) of the Tucuruí hydropower reservoir being in operation, in units of tons of carbon, added up to 6.82 × 103 for CH4 and 1.19 × 106 for CO2. We show that in situ GHG sampling using small floating gas chambers and high precision gas chromatography can be combined with geospatial interpolation techniques and remote sensing data to obtain estimates of diffusive GHG emissions from large water bodies with fluctuating water surfaces such as hydropower reservoirs. We recommend that more measurements and observations on these emissions are pursued in order to support and better quantify the ongoing discussions on estimates and mitigation of GHG emissions from reservoirs in the Amazon region and elsewhere in the world.

The Development of a True Boiling Point Distillation Apparatus

A new true boiling point distillation apparatus was designed, fabricated, and tested as part of a larger research effort on characterization studies of condensate fluids. Mixtures from heptanes, C6, to dodecanes, C12, were separated under atmospheric conditions and from tridecanes, C13, to nonadecanes, C19, under vacuum conditions. Benchmarking of the results from true boiling point analyses was performed by high-precision gas chromatography. Such data are not only scarce but those available indicate differences ranging from 20 to 30% mainly due to carryover of volumes outside the boiling range. This work has shown a difference of less than 10%, which indicates that this new true boiling point equipment is capable of producing results suitable for conducting reservoir fluids characterization studies.

Characterization of trace gases measured over Alberta oil sands mining operations: 76 speciated C<sub>2</sub>–C<sub>10</sub> volatile organic compounds (VOCs), CO<sub>2</sub>, CH<sub>4</sub>, CO, NO, NO<sub>2</sub>, NO<sub>y</sub>, O<sub>3</sub> and SO<sub>2</sub>

Abstract. Oil sands comprise 30% of the world's oil reserves and the crude oil reserves in Canada's oil sands deposits are second only to Saudi Arabia. The extraction and processing of oil sands is much more challenging than for light sweet crude oils because of the high viscosity of the bitumen contained within the oil sands and because the bitumen is mixed with sand and contains chemical impurities such as sulphur. Despite these challenges, the importance of oil sands is increasing in the energy market. To our best knowledge this is the first peer-reviewed study to characterize volatile organic compounds (VOCs) emitted from Alberta's oil sands mining sites. We present high-precision gas chromatography measurements of 76 speciated C2–C10 VOCs (alkanes, alkenes, alkynes, cycloalkanes, aromatics, monoterpenes, oxygenated hydrocarbons, halocarbons and sulphur compounds) in 17 boundary layer air samples collected over surface mining operations in northeast Alberta on 10 July 2008, using the NASA DC-8 airborne laboratory as a research platform. In addition to the VOCs, we present simultaneous measurements of CO2, CH4, CO, NO, NO2, NOy, O3 and SO2, which were measured in situ aboard the DC-8. Carbon dioxide, CH4, CO, NO, NO2, NOy, SO2 and 53 VOCs (e.g., non-methane hydrocarbons, halocarbons, sulphur species) showed clear statistical enhancements (1.1–397×) over the oil sands compared to local background values and, with the exception of CO, were greater over the oil sands than at any other time during the flight. Twenty halocarbons (e.g., CFCs, HFCs, halons, brominated species) either were not enhanced or were minimally enhanced (<10%) over the oil sands. Ozone levels remained low because of titration by NO, and three VOCs (propyne, furan, MTBE) remained below their 3 pptv detection limit throughout the flight. Based on their correlations with one another, the compounds emitted by the oil sands industry fell into two groups: (1) evaporative emissions from the oil sands and its products and/or from the diluent used to lower the viscosity of the extracted bitumen (i.e., C4–C9 alkanes, C5–C6 cycloalkanes, C6–C8 aromatics), together with CO; and (2) emissions associated with the mining effort, such as upgraders (i.e., CO2, CO, CH4, NO, NO2, NOy, SO2, C2–C4 alkanes, C2–C4 alkenes, C9 aromatics, short-lived solvents such as C2Cl4 and C2HCl3, and longer-lived species such as HCFC-22 and HCFC-142b). Prominent in the second group, SO2 and NO were remarkably enhanced over the oil sands, with maximum mixing ratios of 38.7 ppbv and 5.0 ppbv, or 383× and 319× the local background, respectively. These SO2 levels are comparable to maximum values measured in heavily polluted megacities such as Mexico City and are attributed to coke combustion. By contrast, relatively poor correlations between CH4, ethane and propane suggest low levels of natural gas leakage despite its heavy use at the surface mining sites. Instead the elevated CH4 levels are attributed to methanogenic tailings pond emissions. In addition to the emission of many trace gases, the natural drawdown of OCS by vegetation was absent above the surface mining operations, presumably because of the widespread land disturbance. Unexpectedly, the mixing ratios of α-pinene and β-pinene were much greater over the oil sands (up to 217 pptv and 610 pptv, respectively) than over vegetation in the background boundary layer (20±7 pptv and 84±24 pptv, respectively), and the pinenes correlated well with several industrial tracers that were elevated in the oil sands plumes. Because so few independent measurements from the oil sands mining industry exist, this study provides an important initial characterization of trace gas emissions from oil sands surface mining operations.

TBP and chromatographic data for gas condensates characterisation

Gas condensate fluids require accurate characterization for use in the equations of state used in reservoir modelling for field development planning. The most useful data for the computations are determined from single carbon number (SCN) fractions which are obtained by True Boiling Point (TBP) distillations and high precision gas chromatography (GC). TBP analysis requires careful calibration and operation to minimize the amount of overlap outside the boiling range of the fraction. Tests conducted with a TBP apparatus using mixtures of pure components showed differences of mainly less than 3% between the weight % of the separated components and the original weight % of the pure components in the mixture. The TBP gives separated fluids which can be used to determine specific gravity, molecular weight and other PVT information. GC analysis cannot provide these data, but provides a more precise analysis of SCN composition than the TBP. The limited data available in the open literature for comparison can show differences ranging up to 30% due to imperfect separation by TBP. However we obtained differences of mainly less than 8%. The relative closeness of SCN composition allows the use of the high precision GC for benchmarking results from TBP. The SCN weight average boiling points determined from TBP and GC data showed differences of less than 0.5% which further validate the quality of SCN fractions that can be derived by TBP and which can be used in gas condensates characterization studies where experimental data are unavailable.

Ethanol/water solutions as certified reference materials for breath alcohol analyzer calibration

The Federal Institute for Materials Research and Testing (BAM), Germany, has issued a series of large volume ethanol in water certified reference materials (CRMs), primarily developed for the calibration of evidential breath alcohol analyzers in Germany. The certified parameter is the ethanol mass concentration at 20 °C. When used in a wet bath simulator, the solutions deliver gas samples that meet the requirements set by the Organization of Legal Metrology for calibration of breathalyzers. The materials were prepared gravimetrically by spiking of ethanol into water in single 5 L units. A complete uncertainty budget for the preparation process has been established. The purity of the commercial ethanol stock solution was identified to be the main source of uncertainty. For stability and homogeneity measurements and for the verification of the gravimetric mass concentration of the CRMs, a robust high-precision gas chromatography, with flame-ionization detection method for ethanol determination in aqueous samples was developed and validated. The good performance of this method has been demonstrated in several international comparisons organized by the Consultative Committee for Amount of Substance—Metrology in Chemistry at the International Bureau of Weights and Measures.

Simultaneous Measurement of Desaturase Activities Using Stable Isotope Tracers or a Nontracer Method

We report here methods for simultaneous determination ofin vitrodesaturase activities using stable isotope tracers or using a nontracer method in place of radiotracers. Rat microsomal Δ6- and Δ9-desaturase activities were assayed using standard incubationmedium by monitoring the increase in product dueto the reactions [U-13C]18:2n-6 → [U-13C]18:3n-6 or [U-13C]16:0 → [U-13C]16:1n-7, respectively. The stable isotope measurements were made by high-precision gas chromatography–combustion isotope ratio mass spectrometry. Reaction-dependent changes in product or substrate concentrations were also monitored quantitatively by conventional capillary gas chromatography with flame-ionization detection. Desaturase activities calculated from these data are consistent with tracer results. Microsomal Δ5-desaturase activity was monitored by quantifying the decrease in unlabeled substrate mass using the reaction 20:3n-6 → 20:4n-6. All activities showed the expected dependencies on time, temperature, pH, and microsome and substrate concentrations and were well within the range of published activities. Activities in brain, liver, kidney, and heart microsome preparations measured with either labeled or nonlabeled substrate were not significantly different, but were highly significantly different from organ to organ. These methods demonstrate a means to measure desaturase activities conveniently without radiotracers and for reactions involving substrates which are not available in labeled form.

Control and Measurement of Carrier Gas Flow Rate for High-Precision Gas Chromatography

ABSTRACT Two computer-compatible mass flow controllers and a mass flow transducer were evaluated by two methods. The first method employed a thermostatted bubble meter for volumetric measurements. The second involved a direct comparison performed either between two flow devices or between a flow device and a differential pressure transducer. The volumetric calibrations exhibited relative standard deviations of approximately 0.1%. However, direct comparison between electronic flow and pressure devices showed short-term resettabilities of better than 0.1% relative standard deviation. Larger day-to-day variations of 0.1 - 0.2% suggested that improved control of ambient conditions might be rewarding.

ChemInform Abstract: THE MOLAR VOLUME AND ENTROPY OF ADSORBED METHANE ON PORASIL

Chemischer InformationsdienstVolume 5, Issue 43 Article ChemInform Abstract: THE MOLAR VOLUME AND ENTROPY OF ADSORBED METHANE ON PORASIL YOSHIO HORI, YOSHIO HORISearch for more papers by this authorRIKI KOBAYASHI, RIKI KOBAYASHISearch for more papers by this author YOSHIO HORI, YOSHIO HORISearch for more papers by this authorRIKI KOBAYASHI, RIKI KOBAYASHISearch for more papers by this author First published: October 29, 1974 https://doi.org/10.1002/chin.197443084AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume5, Issue43October 29, 1974 RelatedInformation

The Molar Volume and Entropy of Adsorbed Methane on Porasil

Abstract With the use of high-precision gas-chromatography, the multilayer adsorption of methane on fused silica beads was precisely measured between 145.0 K and 213.6 K. The molar volume and the partial molar entropy of the adsorbed methane were determined as a function of the temperature. The molar volume in the monolayer region depends much less on the temperature than that of the bulk liquid. However, the molar volume of multilayer adsorbed methane shows a dependence on the temperature similar to that of bulk liquid, which is at a lower temperature. The volume of the monolayer is practically constant under the present experimental conditions. The apparent thickness of the adsorbed monolayer was interpreted in terms of a simple collision model. The partial molar entropy of the adsorbed phase is much lower than that of the saturated bulk liquid. The lower dependence of the molar volume on the temperature and the lower entropy suggest that the freedom of motion of the adsorbed molecules is restricted as compared with those in bulk liquid.

High-Precision Gas Chromatography

A high-precision chromatograph has been used for determination of differential thermodynamic quantities of two gas-liquid systems. Individual α values and consequently Δ(ΔH°) were determined with a precision of ±0.02%. The precision in the measurement of Δ(ΔG°) was ±0.2%. These values represent an order of magnitude improvement over the best previously reported data. Heats of adsorption of hydrocarbons on carbon black and silica gel were also determined with a precision of ±0.6%.