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Quantitative Control (quantitative + control)
Selected AbstractsReagentless Protein Assembly Triggered by Localized Electrical SignalsADVANCED MATERIALS, Issue 9 2009Xiao-Wen Shi Electrode-imposed signals are used to assemble proteins without the need for reactive reagents. The two-step assembly approach uses i) cathodic signals to electrodeposit the amino-polysaccharide chitosan and ii) anodic signals to activate the chitosan film for protein assembly. Proteins are shown to assemble at individual electrode addresses, with spatial selectivity and quantitative control. [source] Controlling the Diameter of Polyaniline Nanofibers by Adjusting the Oxidant Redox Potential,ADVANCED MATERIALS, Issue 3 2007H. Ding A self-assembly process with no external template and no added acidic dopant is reported as a method providing quantitative control over the diameter d of the polyaniline (PANI) nanofibers produced. An experimental formula relating d to the standard redox potential of the oxidants is established. The PANI nanofibers in the figure have d,,,15,nm. [source] Analysis of phenolic acids in honeys of different floral origin by solid-pase extraction and high-performance liquid chromatographyPHYTOCHEMICAL ANALYSIS, Issue 1 2007Burya Dimitrova Abstract The determination of 18 aromatic and arylaliphatic carboxylic acids in honey from different floral origin using solid-phase extraction (SPE) and reversed-phase high performance liquid chromatography (RP-HPLC) is reported. The behaviour of the solutes on SPE cartridges was predicted from preliminary calculations involving the pKa constants of the carboxylic groups, the n -octanol:water partition coefficients and the distribution coefficients at different pH values of the conditioning and washing solvents. The proposed SPE isolation and pre-concentration of the acids was achieved on reversed-phase Bond Elut C18 cartridges using an acetonitrile:tetrahydrofuran (1:1, v/v) elution system. RP-HPLC separations were performed on a Spherisorb ODS-2 column using linear gradient elution with a mobile phase composed of 20 mm phosphate buffer (pH 2.92) and methanol, and with UV detection. The reported SPE and RP-HPLC methods were applied to the analysis of 49 authentic honey samples from various floral sources and the results indicate that they may serve with respect to the quantitative control of a number of phenolic acids in plant-derived foods and medicinal plants. Copyright © 2006 John Wiley & Sons, Ltd. [source] Development and validation of a simple thin layer chromatographic method for the analysis of artemisinin in Artemisia annua L. plant extractsBIOMEDICAL CHROMATOGRAPHY, Issue 5 2008Els Marchand Abstract Owing to the development of parasite resistance to standard antimalarial treatments like chloroquine and sulfadoxine,pyrimethamine, the demand for Artemisia annua, a key ingredient for new and highly effective antimalarial drugs, is huge. Therefore selective and precise methods to determine the content of artemisinin in dry plant material and in raw impure extracts are needed. In this work a method is described for the clear separation and extraction of artemisinin from other plant components in the Artemisia annua L. plant by thin-layer chromatography (TLC). To obtain optimal extraction and recovery efficiency, several parameters were evaluted, including choice of extraction solvent, TLC plate type and sensitivity between UV and visible light. Method validation was performed on both the dry plant material and non-purified plant extracts. Toluene presented the highest extraction efficiency compared with petroleum ether, hexane and methanol. Reversed-phase plates showed more concentrated spots than normal-phase plates, while the sensitivity of the analysis in UV was comparable to that in visible light but less precise. The impure plant extracts were analyzed by both TLC and HPLC-UV at 215 nm and both methods met the requirements for linearity, selectivity, precision and accuracy. Hence, the proposed TLC method can easily be used for both qualitative and quantitative control of the raw plant extract in areas where advanced methods are scarce. Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||