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A highly sensitive and reproducible isocratic liquid chromatographic method has been developed for the analysis of artemisinin and its three commonly used derivatives (artesunate, dihydroartemisinin, and artemether). The method involves a precolumn derivatization reaction with 4-carboxyl-2,6-dinitrobenzene diazonium ion to produce azo adducts that are UV-active. The critical parameters for the derivatization such as temperature, reaction time, and reagent concentrations were studied and optimized. The chromatographic separations were carried out on a C-18 column with mobile phase consisting of acetonitrile-0.1% acetic acid (60:40) at a flow rate of 1 mL min−1. UV detection was set at 254 nm. Dynamic linear calibration range was obtained at concentrations of artemisinins ranging from 0.26 to 1.44 μg mL−1. The low limits of detections of artemisinin, artesunate, dihydroartemisinin, and artemether were found to be 0.091, 0.0125, 0.0489, and 0.0128 ng μL−1, respectively. The developed methods were precise (RSD <3%) and accurate (% error < 5%). The developed methods may find application in dosage form analysis and pharmacokinetic studies.

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Thermal decomposition of the carbon nanotube/SiO2precursor powders

Thermal analysis coupled with mass spectrometry

Journal of Thermal Analysis and Calorimetry
Authors: H. Yu, C. Lu, T. Xi, L. Luo, J. Ning, and C. Xiang


TG-DSC-MS (thermogravimetry-differential scanning calorimetry-mass spectrometry) coupling techniques were used to make a simultaneous characterizing study for the thermal decomposition process of the carbon nanotube (CNT)/SiO2precursor powders prepared by rapid sol-gel method. The thermal stability of the CNT and the SiO2pure gel were investigated by TG-DSC. The results showed that the oxidation of CNT began from 530 and combusted at about 678C at the heating rate of 10C min-1in air. Moreover, the faster the heating rate, the higher the temperature of CNT combustion. The appropriate calcinations temperature of the CNT/SiO2precursor powders should be held for 1 h at 500C.

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The power-time curves of the growth of three strains of petroleum bacteria at different temperatures have been determined. A novel equation of a power-time curve has been proposed in this paper. The general formula to calculate the rate constant of the bacterial growth has been derived. The rate constants of the bacterial growth at different temperatures, the heat production per newly formed bacterium, the bacterial number at the end of the bacterial growth and the deceleration rate constant of the bacterial growth at 50.00°C, have been calculated. The optimum growth temperatures of the three strains have been obtained.

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Higher plant population and nitrogen management is an adopted approach for improving crop productivity from limited land resources. Moreover, higher plant density and nitrogen regimes may increase the risk of stalk lodging, which is a consequence of complex interplant competition of individual organs. Here, we aimed to investigate the dynamic change in morphology, chemical compositions and lignin promoting enzymes of the second basal inter-nodes altering lodging risk controlled by planting density and nitrogen levels. A field trial was conducted at the Mengcheng research station (33°9′44″N, 116°32′56″E), Huaibei plain, Anhui province, China. A randomized complete block design was adopted, in which four plant densities, i.e., 180, 240, 300, and 360 × 104 ha−1 and four N levels, i.e., 0, 180, 240, and 300 kg ha−1 were studied. The two popular wheat varieties AnNong0711 and YanNong19 were cultivated. Results revealed that the culm lodging resistance (CLRI) index of the second basal internodes was positively and significantly correlated with light interception, lignin and cellulose content. The lignin and cellulose contents were significantly and positive correlated to light interception. The increased planting density and nitrogen levels declined the lignin and its related enzymes activities. The variety AnNong0711 showed more resistive response to lodging compared to YanNong19. Overall our study found that increased planting densities and nitrogen regimes resulted in poor physical strength and enzymatic activity which enhanced lodging risk in wheat varieties. The current study demonstrated that stem bending strength of the basal internode was significantly positive correlated to grains per spike. The thousand grain weight and grain yield had a positive and significant relationship with stem bending strength of the basal internode. The results suggested that the variety YanNong19 produces higher grain yield (9298 kg ha−1) at density 240 × 104 plants ha−1, and 180 kg ha−1 nitrogen, while AnNong0711 produced higher grain yield (10178.86 kg ha−1) at density 240 × 104 plants ha−1 and with 240 kg ha−1 nitrogen. Moreover, this combination of nitrogen and planting density enhanced the grain yield with better lodging resistance.

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