Wyniki wyszukiwania - BazTech

1

Analysis of chloramphenicol in drinking water using an evaporation preparative step and isotope dilution liquid chromatography–tandem mass spectrometry

Li Y., Liu X., Zhang R., ZomPa D., Luo P., Tang L., Liu X., Zhou Y., Wen S.

Acta Chromatographica

|

2018

|

Vol. 30, no. 1

17--20

EN

A reliable isotope dilution method for the determination of chloramphenicol (CAP) in drinking water was developed by using an evaporation preparative step. Each sample was monitored by ultrahigh-pressure liquid chromatography (UHPLC) coupled to tandem mass spectrometry (MS/MS) using an electrospray ionization interface (ESI) in negative ion modes. Recoveries of spiked samples were in the range from 93.2% to 95.7% with intra-day relative standard deviation lower than 6.7% and inter-day relative standard deviation lower than 8.2%. Limit of quantification (LOD) was 0.002 ng/mL. The developed method was successfully applied to the analysis of CAP in drinking water of Shannan region of Tibet.

2

A validated RP-HPLC method for quantitative determination of related impurities of cholic acid bulk drugs

Sheng Z., Ye R., Ge S., Wang C., Xu X., Zhang G., Luo P.

Acta Chromatographica

|

2018

|

Vol. 30, no. 2

114--118

EN

An efficient and convenient reversed-phase high-performance liquid chromatography method has been developed and validated for the quantitative determination of cholic acid bulk drugs and their related impurities. Chromatographic separation was performed on a YMC-Pack ODS-AQ column (250 mm × 4.6 mm, S-5 μm, 12 nm), and the mobile phase consisted of acetonitrile, methanol, and diluted formic acid solution (pH 2.5) at a flow rate of 1.0 mL/min. The analytes were monitored using a refractive index detector at 30 °C, and the column temperature was 30 °C. Under the above chromatographic conditions, the method has good specificity and specified impurities can be effectively separated. The proposed method is found to have linearity in the 2.0–80.0 μg/mL concentration range with correlation coefficients of not less than 0.9999. The compounds analyzed in the solutions are stable for at least 7 days, and spike recoveries for all specified impurities range from 91.3% to 109.3% with relative standard deviations (RSDs) not more than 7.3%. The limit of detection and the limit of quantification for the analytes are 0.060 μg/mL and 2.0 μg/mL, respectively. The proposed method can be applied in the quality control assay of cholic acid bulk drugs, with the advantages of simplicity, accuracy, robustness, good selectivity, and high sensitivity.

3

Theoretical investigation of vanadium oxide film with surface microstructure

Hong W., Wang Z., Chen Q., Sheng C., Gu G., Luo P., Xie Y.

Optica Applicata

|

2017

|

Vol. 47, nr 4

601--609

EN

This paper presents a method to design a surface microstructure of vanadium oxide to enhance optical absorption. This method, using a density of eigenfrequency, can be calculated by a planar wave expand method, to indicate the absorption efficiency of a dispersion material, which can be used as an approach method for further design. Based on this, a nanostructure-based vanadium oxide film is designed and simulated to validate this method. The simulation results show that the tendency of density of eigenfrequency is corresponding to the tendency of optical absorption enhancement. Moreover, this structure can achieve high optical broadband absorption when the material dispersion is considered. High optical absorption enhancement can be achieved by adjusting the geometrical parameters; our maximum overall enhancement absorption ratio was 31.84% at the metal phase, which can be attributed to the enhancement effect of a photonic band edge.

4

Winter methane emission from an alpine open fen on Tibetan Plateau

Zhu D., Chen H., Wu N., Wang Y., Luo P.

Polish Journal of Ecology

|

2011

|

Vol. 59, nr 1

87-94

EN

Methane (CH4) emission was measured from an open fen on the Zoige Plateau (3500 m a.s.l.) (the eastern edge of the QinghaiTibetan Plateau) during two winters of 2006 and 2007. Three dominant plant stands, including Carex muliensis Hand-Mazz. (CM), Eleocharis valleculosa Ohwif. setosa (Ohwi) Kitagawa.(EV) and Kobresia tibetica Maxim (KT) were chosen to be monitored. Winter CH4 emissions were roughly estimated to be 0.94 mg CH4 m[^-2] h[^-1]. High spatialtemporal variations of the emission were found in this fen (the sequence of CM> EV> KT; 0.63 and 1.24 mg CH4 m[^-2] h[^-1] for 2006 and 2007, respectively). Factors involved in the spatial-temporal variation were: 1) water table in summer determining the winter amount of "old" CH4 stored in peat; 2) ice layer determining the release of CH4; 3) plant growth determining both the quantity of CH4 stored in peat and available substrates for CH4 production in winter. However, due to the homogeneity of freezing in winters, predictive factors such as plant growth and water table in summer could contribute more to winter CH4 emission than in situ freezing conditions. Considering that plant growth and water table are also the key factors controlling the spatial-temporal variation of CH4 emission in summer, we therefore suggested that winter CH4 emission represents the "inertia" of summer CH4 emission.

5

Impacts of vegetation type on soil phosphorus availability and fractions near the alpine timberline of the Tibetan Plateau

Zhang L., Wu Y., Wu N., Luo P., Liu L., Hu H.

Polish Journal of Ecology

|

2011

|

Vol. 59, nr 2

307-316

EN

Soil phosphorus (P) availability and fractions are influenced to a large extent by land use and cover changes. Inorganic P (IP) and organic P (OP) fractions in surface soils (0-20 cm) under typical vegetation types, including subalpine coniferous forests, alpine shrubs, and alpine shrub-meadows, near the alpine timberline of the eastern Tibetan Plateau of China, were measured by a modified Hedley fraction method. The results showed that OP is the dominant soil P fraction and the main source of available P in alpine soils near the timberline. Soil organic carbon, total nitrogen, and total P contents were higher in subalpine coniferous forests than in alpine shrubs and alpine shrub-meadows. Concentrations of soil labile P (the sums of Resin-IP, NaHCO3-IP, and NaHCO3-OP) were higher in subalpine coniferous forests than in alpine shrubs and alpine shrub-meadows, an observation that may be partially ascribed to the presence of deep litter layers generated by trees. Concentrations of soil labile and moderately organic P (NaHCO3-OP and NaOH-OP) in subalpine coniferous forests were also greater than in alpine shrubs and alpine shrub-meadows. Greater amounts of soil stable OP (extracted by concentrated HCl and cHCl.OP) were accumulated in alpine shrub-meadows compared to alpine shrubs or subalpine coniferous forests. The reduced availability of OP may be attributed mainly to increasing recalcitrant soil organic matter input in alpine shrub-meadows and alpine shrubs. Concentrations of IP associated with Ca minerals and parent materials (extracted by diluted HCl and HCl-IP, and extracted by concentrated HCl and cHCl-IP, respectively) were lower in subalpine coniferous forests, indicating that coniferous forests are more likely to use recalcitrant IP than alpine shrubs and alpine shrub-meadows. In this alpine region, land cover changes from subalpine coniferous forests to alpine shrubs and alpine shrub-meadows near the alpine timberline could decrease soil P conservation, availability, and supplementation.

6

Effects of freezing and freeze-thaw cycles on soil microbial biomass and nutrient dynamics under different snow gradients in an alpine meadow (tibetan plateau)

Liu L., Wu Y., Wu N., Luo P., Xu J., Mao Y., Zhang L.

Polish Journal of Ecology

|

2010

|

Vol. 58, nr 4

717-728

EN

In alpine zones, cold season processes, particularly those associated with snow accumulation and ablation, have a central role in ecosystem functioning. However, we know very little about soil carbon and nitrogen processes under the snowpack in these ecosystems, including the Tibetan Plateau. We conducted an experiment comparing three snow regimes (11 m x 1 m plots) of different snow depths and durations at an altitude of 4,100 m in the Minshan Range on the eastern Tibetan Plateau. The three snow regimes included a shallow and short duration snowpack (SS; depth <10 cm), a moderate snow depth and medium duration snowpack (MS; depth <20 cm), as well as a deep and long duration snowpack (DS; depth > 30 cm). This study explores the effects of different snow conditions on soil temperature, and further describes the sequence and timing of dissolved nutrients and microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) in soils under different snow regimes during the autumn-winter transition (i.e. November 7, 2008 - March 7, 2009). Three successive phases of temperature change were distinguished: I - initial decline - soil temperatures dropped steadily from 4[degrees]C to about 0[degrees]C at the same rate for all three snow regimes; II - moderate freezing - soil temperatures fluctuated between 0[degrees]C and -7[degrees]C under all three snow regimes; III - multiple freeze-thaw cycles took place in the SS and MS regimes, but permanent freezing occurred in the DS regime. Under moderate freezing, we found that soil temperature fluctuation was an essential factor for the transformation of soil C and N. Our results indicate that larger temperature fluctuations correlate with a greater increase in dissolved organic nitrogen (DON) content. Dissolved organic carbon (DOC) content increased markedly only under the most drastic temperature fluctuations. In contrast, MBC content increased significantly only when soil temperatures were relatively steady. Under the permanent freezing, only a large number of freeze-thaw cycles caused a significant decline of NO[^][3] -N and DOC concentrations. DON content declined markedly under permanent freezing and multiple freeze-thaw cycles. However, MBC content declined significantly only under permanent freezing. Ultimately, multiple freeze-thaw cycles resulted in the export of dissolved nutrients (organic and inorganic nitrogen) from the alpine ecosystem which had previously accumulated in the moderate freezing phase of the soil.

7

Simulation of light regimes in typical subalpine forest succession series of eastern Tibetan Plateau

Wang Q., Wu N., Luo P.

Polish Journal of Ecology

|

2009

|

Vol. 57, nr 2

251-260

EN

Natural regeneration of forest depends on the light regimes of floor. Point-based methods such as fisheye photo and radiometer can not provide a full panorama of light regime of heterogeneous forest stand. Eastern Tibetan Plateau is a major forest belt characteristic of diverse forest type and topographic differentiation. Understanding the trend of changes of light regime along succession series of forest may be helpful for the management of ecosystems. Fragmented forest patches due to tectonic activity and human intervention have made this prediction difficult. We use a spatially explicit forest stand light model (tRAYci) to simulate light distribution within forest in typical subalpine forest succession series of eastern Tibetan Plateau. Due to the spatial heterogeneity of tree distribution in the subalpine area, the forest stand can be approximated with a spatially explicit model of trees. Three typical subalpine forest stands (Sabina forest (SF), Fir forest (FF) and Birch forest (BF)) are selected in the eastern Tibetan Plateau. The dominant species are sabina (Sabina saltuaria (Rehd. et Wils.) Cheng), fir (Abies faxoniana Rehd. et Wils.) and birch (Betula platyphylla Suk.) for each stand and they are spatially clumped in distribution. They represent old growth coniferous forest (SF, 330 years old), coniferous-broadleaved forest (FF, 180 ys) and pioneer broadleaved forest (BF, 40 ys). The parameters of the three-dimensional model of trees are calibrated with field measurements. The simulated values are generally consistent with observed values of radiation measured by radiometers installed in these stands and values derived from fisheye photos. Test failures may be caused by the incomplete submodel of crown as a gap free one. Light regimes in old growth and pioneer forest are much more heterogeneous than intermediate stages of forest. Light regimes of these forests are also reflected by the composition of understory herb layers.