Extraction of Nitraria tangutorum seed oil by supercritical carbon dioxide and determination of free fatty acids by HPLC/APC/IMS with fluorescence detection

The seed oil from Nitraria tangutorum samples was obtained by supercritical carbon dioxide extraction methods. The extraction parameters for this methodology, including pressure, temperature, particle size and extraction time, were optimized. The free fatty acids in the seed oil were separated with a pre-column derivation method and 1,2-benzo-3,4-dihydrocarbazole-9-ethyl-p-toluenesulfonate (BDETS) as a labeling regent, followed by high-performance liquid chromatography (HPLC) with fluorescence detection. The target compounds were identified by mass spectrometry with atmospheric pressure chemical ionization (APCI in positive-ion mode). HPLC analysis shows that the main compositions of the seed oil samples were free fatty acids (FFAs) in high to low concentrations as follows: linoleic acid, oleic acid, hexadecanoic acid and octadecanoic acid. The assay detection limits (at signal-to-noise of 3:1) were 3.378-6.572 nmol/L. Excellent linear responses were observed, with correlation coefficients greater than 0.999. The facile BDETS derivatization coupled with mass spectrometry detection allowed the development of a highly sensitive method for analyzing free fatty acids in seed oil by supercritical CO2 extraction. The established method is highly efficient for seed oil extraction and extremely sensitive for fatty acid profile determination. (C) 2007 Elsevier B.V. All rights reserved.

Short-term effects of sheep excrement on carbon dioxide, nitrous oxide and methane fluxes in typical grassland of Inner Mongolia

Excrement patches of grazing animals play an important role in greenhouse gas (GHG) fluxes due to the high nitrogen (N) and available carbon (C) deposited in small areas, but little information is available for the effect of excrement in the Inner Mongolian grassland (43 26 degrees N, 116 degrees 40'E). To elucidate the effect of grazing sheep urine, fresh dung and compost on fluxes of methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O), a short-term field study (65 days) was carried out in the typical grassland of Inner Mongolia with the optimised closed chamber/GC technique. Compared with the control, cumulative net CH4 consumption decreased 36, 31, and 18% from urine, fresh dung, and compost plots, respectively; net CO2-C output increased by 6.5, 1.5, and 1.2% from urine, fresh dung, and compost treated soil, respectively; about three times as much N2O-N was emitted from urine and the fresh dung treatments during 65 days. Nitrous oxide emission was positively correlated with CO, emission (R = 0.691, P < 0.01) and water-filled pore space (R = 0.698, P < 0.01). The percentages of N2O-N loss of applied-N were 0.44 and 1.05% for urine and fresh dung, respectively. Our results suggest that in autumn in the degraded grassland of Inner Mongolia, the effect of sheep excrement may be ignored when evaluating the total GHG emissions.

Carbon dioxide dynamics and controls in a deep-water wetland on the Qinghai-Tibetan Plateau

To initially characterize the dynamics and environmental controls of CO2, ecosystem CO2 fluxes were measured for different vegetation zones in a deep-water wetland on the Qinghai-Tibetan Plateau during the growing season of 2002. Four zones of vegetation along a gradient from shallow to deep water were dominated, respectively by the emergent species Carex allivescens V. Krez., Scirpus distigmaticus L., Hippuris vulgaris L., and the submerged species Potamogeton pectinatus L. Gross primary production (GPP), ecosystem respiration (Re), and net ecosystem production (NEP) were markedly different among the vegetation zones, with lower Re and GPP in deeper water. NEP was highest in the Scirpus-dominated zone with moderate water depth, but lowest in the Potamogeton-zone that occupied approximately 75% of the total wetland area. Diurnal variation in CO2 flux was highly correlated with variation in light intensity and soil temperature. The relationship between CO2 flux and these environmental variables varied among the vegetation zones. Seasonal CO2 fluxes, including GPP, Re, and NEP, were strongly correlated with aboveground biomass, which was in turn determined by water depth. In the early growing season, temperature sensitivity (Q(10)) for Re varied from 6.0 to 8.9 depending on vegetation zone. Q(10) decreased in the late growing season. Estimated NEP for the whole deep-water wetland over the growing season was 24 g C m(-2). Our results suggest that water depth is the major environmental control of seasonal variation in CO2 flux, whereas photosynthetic photon flux density (PPFD) controls diurnal dynamics.

Carbon dioxide exchange between the atmosphere and an alpine meadow ecosystem on the Qinghai-Tibetan Plateau, China

We used the eddy covariance method to measure the M exchange between the atmosphere and an alpine meadow ecosystem (37degrees29-45'N, 101degrees12-23'E, 3250m a.s.l.) on the Qinghai-Tibetan Plateau, China in the 2001 and 2002 growing seasons. The maximum rates Of CO2 uptake and release derived from the diurnal course Of CO2 flux (FCO2) were -10.8 and 4.4 mumol m(-2) s(-1), respectively, indicating a relatively high net carbon sequestration potential as compared to subalpine coniferous forest at similar elevation and latitude. The largest daily CO2 uptake was 3.9 g cm(-2) per day on 7 July 2002, which is less than half of those reported for lowland grassland and forest at similar latitudes. The daily CO2 uptake during the measurement period indicated that the alpine ecosystem might behave as a sink of atmospheric M during the growing season if the carbon lost due to grazing is not significant. The daytime CO2 uptake was linearly correlated with the daily photosynthetic photon flux density each month. The nighttime averaged F-CO2 showed a positive exponential correlation with the soil temperature, but apparently negative correlation with the soil water content. (C) 2004 Elsevier B.V. All rights reserved.

Syngas production using an oxygen-permeating membrane reactor with cofeed of methane and carbon dioxide

CH4-CO2-O-2 reforming to syngas in a never Ba0.5Sr0.5Co0.8Fe0.2O3.delta oxygen-permeable membrane reactor using LiLaNiO/gamma-Al2O3 as catalyst was successfully reported. Excellent reaction performance was achieved with around 92% methane conversion efficiency, 95% CO2 conversion rate, and nearly 8.5mL/min.cm(2) oxygen permeation flux. In contrast to the oxygen permeation model with the presence of large concentration of CO2 (under such condition the oxygen permeation flux deteriorates with time), the oxygen permeation flux is really stable under the CH4CO2-O-2 reforming condition.