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991.
Microwave-assisted extraction (MAE) was carried out for the simultaneous determination of the insecticides thiamethoxam [(EZ)-3-(2-chloro-1,3-thiazol-5-ylmethyl)-5-methyl-1,3,5-oxadiazinan-4-ylidene(nitro)amine], imidacloprid [1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine], and the fungicide carbendazim (methyl benzimidazol-2-ylcarbamate) in vegetable samples. Five crop samples consisting of cabbage, tomatoes, chilies, potatoes, and peppers were fortified with the three pesticides and subjected to MAE followed by cleanup to remove coextractives prior to analysis by high-performance liquid chromatography. Using the selected microwave exposure time and power setting, the recoveries of the three pesticides from the fortified vegetable samples ranged from 68.1 to 106%. The corresponding recoveries for samples processed simultaneously but without microwave exposure ranged from 37.2 to 61.4%. The recoveries by MAE were comparable to those obtained by the conventional blender extraction technique. The precision of the MAE method was demonstrated by relative standard deviations of <7% for the three pesticides. The cooked cabbage and tomato samples showed no breakdown of the parent compounds, and the recoveries of three pesticides were comparable to those obtained with the uncooked samples. 相似文献
992.
The treatment of perchloroethylene (PCE) was investigated by the promotion of Fenton-like reactions using the iron oxyhydroxide goethite (α-FeOOH) as the sole source of the iron catalyst. A silica sand-goethite matrix was contaminated with 5 mg L?1 PCE and the oxidative treatments were conducted with 0.15 mM, 2 mM, 5mM, 10mM, 20mM, and 30mM H2O2. Perchloroethylene was effectively degraded within 96 hr and the most efficient treatment stoichiometry was observed using 0.15 mM H2O2 at pH 3. The degree of heterogeneous catalysis was evaluated by conducting oxidation reactions in parellel systems with an equivalent concentration of soluble iron. The results showed that, within the first 24 hr, up to 94% of the PCE degradation was attributed to heterogeneous catalysis. This modified Fenton's process, when used to treat 5 mg L?1 PCE in natural subsurface materials with 2 mM H2O2 at pH 3, resulted in a residual of 0.20 mg L?1 PCE after 96 hr. 相似文献
993.
Gian Gupta Ravinder Sandhu Jeanine Harter-Dennis Arslan Khan 《Water, air, and soil pollution》1988,38(3-4):325-332
Airborne dust particles were sampled in a broiler house using the quartz crystal microbalance cascade impactor designed for the measurement of mass concentration and size distribution from 0.05 to 25 gm. No significant difference was noticed in the dust concentration from morning to evening or at different sampling sites in the broiler house. The concentration of airborne dust particles decreased as the age of the chickens increased. Ratio of dust particles smaller than 0.8 pm to the total dust ranged from 10 to 50%. The highest concentration of dust was in the particle size range of 3.2 μm. The fogging system in use reduced the concentration of larger particles but not that of the smaller particles. 相似文献
994.
995.
The amount of triacylglycerol (TG) in the surface monolayer of intact phospholipid-stabilized emulsions was determined using (13)C nuclear magnetic resonance ((13)C NMR). (13)C NMR spectra of emulsions composed of bulk long-chain or medium-chain TG were prepared with [(13)C(3)]-carbonyl-enriched triolein, tripalmitin, or trioctanoin, and were analyzed and compared with NMR spectra of phosphatidylcholine vesicles with and without added TG. Identification of carbonyl peaks intermediate between those of phosphatidylcholine carbonyls and bulk TG confirmed the presence of surface TG in each emulsion. The surface of emulsions contained 2.2 mol % tripalmitin and 1.4 mol % triolein, but significantly more medium-chain TG, 9.1 mol % trioctanoin, as predicted by measurements of TG in phospholipid vesicles. Thus, medium-chain TGs are more accessible than long-chain TGs to enzymes or pro-oxidants in the continuous phase of phospholipid-stabilized emulsion systems. The quantitative determination of surface-located TG in intact particles will advance the understanding of emulsion colloidal properties, physicochemical stability, and metabolic behavior. 相似文献
996.
Khalid Usman Samee Ud Din Inam ullah Said Ghulam Muhammad Waqas Imam Malik Muhammad Saad 《Communications in Soil Science and Plant Analysis》2020,51(11):1423-1433
ABSTRACT Sulfur (S) availability is a characteristic of conservation tillage. We studied the effects of S on sunflower yield and fatty acid profile under conventional and conservation tillage in silty clay soil of D.I. Khan, Pakistan. Conventional tillage consisted of disk plowing followed by tiller and rotavator, while conservation tillage comprises tiller and disc harrowing. Treatments comprise six sulfur levels (S1 = 0, S2 = 20 kg S ha?1 at sowing, S3 = 10 kg S ha?1 at sowing +10 kg S ha?1 25 days after sowing (DAS), S4 = 40 kg S ha?1 at sowing, S5 = 20 kg S ha?1 at sowing + 20 kg S ha?1 25 DAS, and S6 = 20 kg S ha?1 at sowing + 10 kg S ha?1 25 DAS + 10 kg S ha?1 50 DAS) replicated thrice. After 2 years of experimentation, soil samples were collected (from 0 to 0.30 m depth) for organic matter (OM), total soil N (TSN), and available sulfur analysis. Conservation tillage significantly increased OM, TSN, and S contents in 0–0.30 m soil compared to conventional tillage. Likewise, sunflower plants showed higher achene yield, better fatty acid profile, and net economic returns in conservation tillage than in conventional tillage. Application of 20 kg S ha?1 at sowing and 10 kg S ha?1 at each 25 and 50 DAS recorded significantly higher achene yield, higher oil, and linoleic acid contents; however, oleic and oleic/linoleic ratio did not increase with higher S rates. Conservation tillage was effective in increasing OM, TSN, and available S besides increasing yield and economics in silty clay soil. 相似文献
997.
Arsenic Chemistry in Soils: An Overview of Thermodynamic Predictions and Field Observations 总被引:2,自引:0,他引:2
Published information, both theoretical and experimental, on As chemical behavior in soils is reviewed. Because of many emission sources, As is ubiquitous. Thermodynamic calculations revealed that As(V) species (HAsO 4 2- >H2AsO 4 - at pH 7) are more abundant in soil solutions that are oxidized more than pe+pH>9. Arsenic is expected to be in As(III) form (HAsO 2 0 =H3AsO 3 0 >AsO 2 - =H2AsO 3 - at pH 7) in relatively anoxic soil solutions with pe+pH<7. Adsorption on soil colloids is an important As scavenging mechanism. The adsorption capacity and behavior of these colloids (clay, oxides or hydroxides surfaces of Al, Fe and Mn, calcium carbonates, and/or organic matter) are dependent on ever-changing factors, such as hydration, soil pH, specific adsorption, changes in cation coordination, isomorphous replacement, crystallinity, etc. Because of the altering tendencies of soil colloids properties, adsorption of As has become a complex, empirical, ambiguous, and often a self contradicting process in soils. In general, Fe oxides/hydroxides are the most commonly involved in the adsorption of As in both acidic and alkaline soils. The surfaces of Al oxides/hydroxides and clay may play a role in As adsorption, but only in acidic soils. The carbonate minerals are expected to adsorb As in calcareous soils. The role of Mn oxides and biogenic particles in the As adsorption in soils appears to be limited to acidic soils. Kinetically, As adsorption may reach over 90% completion in terms of hours. Precipitation of a solid phase is another mechanism of As removal from soil solutions. Thermodynamic calculations showed that in the acidic oxic and suboxic soils, Fe-arsenate (Fe3(AsO4)4)2) may control As solubility, whereas in the anoxic soils, sulfides of As(III) may control the concentrations of the dissolved As in soil solutions. In alkaline acidic oxic and suboxic soils, precipitation of both Fe- and Ca-arsenate may limit As concentrations in soil solutions. Field observations suggest that direct precipitation of discrete As solid phases may not occur, except in contaminated soils. Chemisorption of As oxyanions on soil colloid surfaces, especially those of Fe oxide/hydroxides and carbonates, is believed to a common mechanisms for As solid phase formation in soils. It is suggested that As oxyanions gradually concentrate on colloid surfaces to a level high enough to precipitate a discrete or mixed As solid phase. Arsenic volatilization is another As scavenging mechanism operating in soils. Many soil organisms are capable of converting arsenate and arsenite to several reduced forms, largely methylated arsines which are volatile. These organisms may generate different or similar biochemical products. Methylation and volatilization of As can be affected by several biotic (such as type of organisms, ability of organism for methylation, etc.) and abiotic factors (soil pH, temperature, redox conditions, methyl donor, presence of other ions, etc.) factors. Information on the rate of As biotransformations in soils is limited. In comparison to the biologically assisted volatilization, the chemical volatilization of As in soils is negligible. 相似文献
998.
J A Khan L Gijs C Berger N Martin G Piraprez H E Spinnler E N Vulfson S Collin 《Journal of agricultural and food chemistry》1999,47(8):3269-3273
A new method for the "one-pot" synthesis of S-methyl thioesters has been developed by reacting methyl chlorothiolformate with carboxylic acids. The resulting "flavor library" contained all the intended thioesters and a single major impurity, identified by GC-MS as S, S-dimethyldithiocarbonate. Quantification of individual compounds present in the library was performed by GC analysis using two independent methods of detection, SCD and FID. It was shown that apart from S-methyl thioacetate (0.8 mol %), molar concentrations of other thioesters varied in a relatively narrow range from 4.2 mol % for S-methyl thiopropionate to 14.1 mol % for S-methyl thiohexanoate. In general, medium chain S-methyl thioesters were present in slightly higher molar concentrations than those prepared from short or long chain carboxylic acids. This variation was attributed to partial loss of the most volatile components during extraction and the lower reactivity of higher homologues. The library was used for the characterization of some physicochemical parameters of thioesters. In particular, lipophilicity coefficients (log k(w)) and thioester retention in 10, 20, and 33% triolein (used as a model lipid phase) were determined directly by reverse-phase HPLC and extrapolated from the respective data. This analysis illustrates that substantial information can be generated using a library containing a relatively large number of compounds in effectively the same way as is necessary for the analysis of a single sample. 相似文献
999.
Khan I Nisar M Shah MR Shah H Gilani SN Gul F Abdullah SM Ismail M Khan N Kaleem WA Qayum M Khan H Obaidullah Samiullah Ullah M 《Fitoterapia》2011,82(7):1003-1007
Current study was conducted to identify constituents of Taxus wallichiana Zucc. that might be responsible for its folk use in anti-inflammatory conditions. Taxusabietane A was isolated from the bark extract of Taxus wallichiana Zucc. Taxusabietane A was analyzed for in-vitro and in-vivo anti-inflammatory activities using Lipoxygenase (LOX) inhibition assay and carrageenan-induced paw edema model. Taxusabietane A revealed considerable LOX inhibitory activity with the IC50 value being 57 ± 0.31. Standard compound Baicalein showed the IC50 value being 22.1 ± 0.03 μM. Taxusabietane A also showed significant (5 and 10 mg/kg) anti-inflammatory activity induced by carrageenan. However, this study highlighted the potential of Taxusabietane A to be further explored as a new lead compound for management of conditions associated with inflammation. 相似文献
1000.
Akhtar Muhammad Uzair Hifzulrahman Imran Muhammad Pasha Talat Naseer Khalique Anjum Saadullah Muhammad Tahir Muhammad Naeem Ikram-ul-Haq Muhammad Naveed-ul-Haque Muhammad 《Tropical animal health and production》2021,53(4):1-10
Tropical Animal Health and Production - The aim of the study was to assess the effect of feeding the same diet to different breeds of chickens and at different ages on fatty acid (FA) composition... 相似文献