1,720,989 research outputs found
Optimization of the Measurement of Italian Monocultivar Extra Virgin Olive Oil Antioxidant Power Via the Briggs–Rauscher Reaction
No full textIn this paper, the overall antioxidant power of monocultivar extra virgin olive oil (EVOO) from Marche Region (Italy) was determined modifying, for the first time, the Briggs–Rauscher (BR) method to account for the water insolubility of the samples. The modification can pave the way to extend the BR antioxidant capacity assay to other real food systems that are usually heterogeneous mixtures and to easily take into account synergistic effects of antioxidants and food matrix that are essential to determine the antioxidant capacity; the pH of the method is the pH of gastric fluids, and this is noteworthy if we take into account that lipid peroxidation is amplified at this pH. The method is simple, rapid, and inexpensive. The interplay among antioxidant activity and total phenol content is rewarding and witness the feasibility of the method for the fast screening of antioxidant activity of EVOO samples
Extended thermodynamic approach to ion interaction chromatography. A mono- and bivariate strategy to model the influence of ionic strength
No full textExtended thermodynamic approach to ion interaction chromatography: effect of the electrical charge of the solute ion
No full textExtended thermodynamic approach to ion interaction chromatography
No full textThe chromatographic behavior of charged analytes in ion interaction chromatography (IIC) is theoretically investigated. The chemical modifications of the stationary and mobile phases in the presence of ion interaction reagent (IIR) are theoretically shown to change the partition coefficient for charged molecules. The most reliable literature experimental results concerning retention behavior of charged molecules in IIC were used to test the new theory. Retention equations are compared with those that can be obtained from the most important retention models in IIC. The present exhaustive retention model, which is well-founded in physical chemistry, goes further than the previous ones whose retention equations can be viewed as limiting cases of the present theory. The present extended thermodynamic approach reduces to stoichiometric or electrostatic retention models if the surface potential or pairing equilibria are respectively neglected. Moreover, it is able to quantitatively explain experimental evidences that cannot be rationalized by the existing retention models
Influence of experimental parameters on chromatographic behavior of neutral molecules in ion interaction chromatography
No full textThe chromatographic behavior of aprotic neutral molecules in Ion Interaction Chromatography (IIC) was investigated both theoretically and experimentally on a styrene-divinylbenzene based C18 stationary phase. The chemical modification of the stationary phase in the presence of Ion Interaction Reagent (IIR) in the eluent, and adsorption competition between tested analytes and IIR for inner layer sites are theoretically shown to change the partition coefficient for neutral molecules. Experimental evidence confirms that their retention decreases with increasing ion-interaction reagent (IIR) concentration in the eluent. The influence of the mobile phase ionic strength on neutral molecules retention was investigated and the dependence of retention modulus on organic modifier concentration in the eluent was elucidated
Ion-Interaction Chromatography of Zwitterions. The Fractional Charge Approach to influence of the mobile phase concentration of the ion interaction reagent
No full textExtended thermodynamic approach to ion interaction chromatography for low surface potential: use of the linearized potential expression
No full textThe chromatographic behaviour of charged analytes in Ion Interaction Chromatography (IIC) was theoretically investigated. Simplified retention equations were obtained via the linearized potential expression. They can be used to model analyte retention as a function of both the mobile and stationary phase concentration of the Ion-Interaction reagent (IIR), if the surface potential is below 25 mV. Simplified retention equations were compared to those, which can be obtained from two of the most important retention models in IIC. They reduce to stoichiometric or electrostatic retention model equations if the surface potential or pairing equilibria are respectively neglected
Ion interaction chromatography of neutral molecules
No full textThe chromatographic behavior of neutral molecules in ion-interaction chromatography (IIC) is investigated theoretically. The physical and chemical modification of the stationary phase in the presence of Ion Interaction Reagent (IIR) in the eluent, and adsorption competition between test analytes and IIR for inner layer sites are shown theoretically to change the partition coefficient of neutral molecules. The most reliable, literature experimental results, concerning retention behaviour of neutral molecules in IIC, were used to test the new theory. The wide variability among them was elucidated on the basis of the exhaustive retention model developed. Retention equations were compared to those which can be obtained, if the charge of the analyte is zero, from the most important retention model in IIC
Ion interaction chromatography of neutral molecules: a potential approximation to obtain a simplified retention equation
No full textThe chromatographic behavior of neutral molecules in Ion Interaction Chromatography (IIC) was theoretically investigated. The use of a potential approximation to obtain a simplified retention equation was successfully tested. The most reliable experimental literature results, concerning the retention behavior of neutral molecules in IIC, were successfully fitted by the retention equation. The wide variability among them was elucidated on the basis of the developed retention equation. A new separation strategy, to improve the selectivity of the chromatographic method, for difficult to separate mixtures of neutral eluates was proposed
Nonlinear kinetic regime of the Weibel instability in an electron-ion plasma
No full textKinetic numerical simulations of the evolution of the Weibel instability during the full nonlinear regime including ions dynamics are presented. The formation of strong density inhomogeneity and its influence on the resulting electrostatic and electromagnetic wave modes are shown. (C) 2002 American Institute of Physics
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