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Additive Concentration (additive + concentration)
Selected AbstractsTwo variable semi-empirical and artificial neural-network-based modeling of peptide mobilities in CZE: The effect of temperature and organic modifier concentrationELECTROPHORESIS, Issue 5 2009Stefan Mittermayr Abstract This work was focused on investigating the effects of two separation influencing parameters in CZE, namely temperature and organic additive concentration upon the electrophoretic migration properties of model tripeptides. Two variable semi-empirical (TVSE) models and back-propagation artificial neural networks (ANN) were applied to predict the electrophoretic mobilities of the tripeptides with non-polar, polar, positively charged, negatively charged and aromatic R group characteristics. Previously published work on the subject did not account for the effect of temperature and buffer organic modifier concentration on peptide mobility, in spite of the fact that both were considered to be influential factors in peptide analysis. In this work, a substantial data set was generated consisting of actual electrophoretic mobilities of the model tripeptides in 30,mM phosphate buffer at pH 7.5, at 20, 25, 30, 35 and 40°C and at four different organic additive containing running buffers (0, 5, 10 and 15% MeOH) applying two electric field strengths (12 and 16,kV) to assess our mobility predicting models. Based on the Arrhenius plots of natural logarithm of mobility versus reciprocal absolute temperature of the various experimental setups, the corresponding activation energy values were derived and evaluated. Calculated mobilities by TVSE and back-propagation ANN models were compared with each other and to the experimental data, respectively. Neural network approaches were able to model the complex impact of both temperature and organic additive concentrations and resulted in considerably higher predictive power over the TVSE models, justifying that the effect of these two factors should not be neglected. [source] Metastable zone determination of lipid systems: Ultrasound velocity versus optical back-reflectance measurementsEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 5 2010Kesarin Chaleepa Abstract The metastable zone width (MZW) of a multi-component system as influenced by the process parameters cooling rate, agitation speed, and additive concentration was determined via ultrasound velocity measurements. The results were compared with those obtained by optical back-reflectance measurements (ORM) using coconut oil as a model substance. Increasing the cooling rate led to the shift of the nucleation point to lower temperatures. This tendency was better visualized by the ultrasonic curves while a significant disturbance of the ORM signal could be observed. Agitation led to an increase of the nucleation temperature and hence a narrower metastable zone. The influence of an additive on the MZW was found to strongly depend on its concentration. The MZW detected by the ultrasound technique was narrower compared to that obtained by the ORM method, indicating the faster response to the phase transition of the ultrasound technique. Another advantage of the ultrasound technique was the in situ evaluation of the experimental data, while ORM needed a linear fitting to estimate the saturation temperature. Furthermore, ultrasound velocity measurements are based on density determination of the medium whereas the ORM sensor is able to detect only particles that are located within the measuring zone and possess a well-defined size. Practical applications: MZW is one of the most important parameters that determine the characteristics of crystalline products. However, a proper technique that can be used in MZW detection in fat systems has rarely been reported, due to the difficulties in dealing with natural fats. The findings of this study can greatly help those who are involved in the field of fat crystallization from both the academic and the practical point of view. This is due to the fact that new and promising techniques for the online and in situ determination of the MZW of fats, with high accuracy, and reproducibility, under most process conditions, were clarified in this work. The readers can easily follow the procedure developed in this paper. Also information about the influence of process parameters and additives on the MZW is included. [source] The Effect of Brine Ingredients on Carrot Texture during Thermal Processing in Relation to Pectin Depolymerization due to the ,-Elimination ReactionJOURNAL OF FOOD SCIENCE, Issue 9 2006Trong Son Vu ABSTRACT:, Thermal texture degradation of carrots was studied at a temperature of 100 °C in aqueous solutions containing sodium chloride, citric acid, ascorbic acid, and ethylenediaminetetraacetic acid (EDTA) at different concentrations. To enhance the texture of the final product, the carrot samples were pretreated at 65 °C for 30 min in an aqueous calcium chloride solution (5 g/L). For all case studies considered, the pH of the solutions was adjusted to pH = 6.0. In parallel, both the changes in degree of esterification (DE) and the progress of the ,-elimination reaction of carrot pectin under the same conditions were investigated. The kinetic parameters for texture degradation (rate constant kt and final texture value [TP,/TP0]) were estimated using a fractional conversion model. The results indicate that both the rate constant for texture degradation (kt) and the rate constant for the ,-elimination reaction (kb) increased with increasing additive concentration, while the final texture values (TP,/TP0) and DE decreased with increasing additive concentration in all systems studied. A high correlation was observed between the relative rate constant for texture degradation and the relative rate constant for the ,-elimination reaction on the one hand, and the relative final texture value and the relative rate constant for the ,-elimination reaction on the other hand, suggesting that the influence of the solutes on texture degradation can be explained by their influence on the ,-elimination reaction. [source] Determination of quinocide as impurity in primaquine tablets by capillary zone electrophoresisBIOMEDICAL CHROMATOGRAPHY, Issue 5 2009Abdalla A. Elbashir Abstract A capillary zone electrophoretic method has been developed and validated for the determination of the impurity quinocide (QC) in the antimalarial drug primaquine (PQ). Different buffer additives such as native cyclodextrins and crown ethers were evaluated. Promising results were obtained when either , -cyclodextrin (, -CD) or 18-crown-6 ether (18C6) were used. Their separation conditions such as type of buffer and its pH, buffer additive concentration, applied voltage capillary temperature and injection time were optimized. The use of 18C6 offers slight advantages over , -CD such as faster elution times and improved resolution. Nevertheless, migration times of less than 5 min and resolution factors (Rs) in the range of 2,4 were obtained when both additives were used. The method was validated with respect to selectivity, linearity, limits of detection and quantitation, analytical precision (intra- and inter-day variability) and repeatability. Concentrations of 2.12 and 2.71% (w/w) of QC were found in pharmaceutical preparations of PQ from two different manufacturers. A possible mechanism for the successful separation of the isomers is also discussed. Copyright © 2008 John Wiley & Sons, Ltd. [source] Additive concentration effects on enantioselective separations in supercritical fluid chromatography,CHIRALITY, Issue 4 2003Karen W. Phinney Abstract Polar additive concentration effects in supercritical fluid chromatography were studied on chiral stationary phases having either a macrocyclic glycopeptide or a derivatized polysaccharide as the chiral selector. Two basic additives, isopropylamine and triethylamine, were incorporated into the methanol modifier at various concentrations and the effects on retention, selectivity, and resolution were monitored. Many of the analytes failed to elute from the macrocyclic glycopeptide stationary phase in the absence of an additive and the most noticeable effect of increasing additive concentration was a significant decrease in retention. On the derivatized polysaccharide stationary phase the additives had little effect on retention, but they did foster significant improvements in peak shape and resolution. Chirality 15:287,294, 2003. Published 2003 Wiley-Liss, Inc. [source] Two variable semi-empirical and artificial neural-network-based modeling of peptide mobilities in CZE: The effect of temperature and organic modifier concentrationELECTROPHORESIS, Issue 5 2009Stefan Mittermayr Abstract This work was focused on investigating the effects of two separation influencing parameters in CZE, namely temperature and organic additive concentration upon the electrophoretic migration properties of model tripeptides. Two variable semi-empirical (TVSE) models and back-propagation artificial neural networks (ANN) were applied to predict the electrophoretic mobilities of the tripeptides with non-polar, polar, positively charged, negatively charged and aromatic R group characteristics. Previously published work on the subject did not account for the effect of temperature and buffer organic modifier concentration on peptide mobility, in spite of the fact that both were considered to be influential factors in peptide analysis. In this work, a substantial data set was generated consisting of actual electrophoretic mobilities of the model tripeptides in 30,mM phosphate buffer at pH 7.5, at 20, 25, 30, 35 and 40°C and at four different organic additive containing running buffers (0, 5, 10 and 15% MeOH) applying two electric field strengths (12 and 16,kV) to assess our mobility predicting models. Based on the Arrhenius plots of natural logarithm of mobility versus reciprocal absolute temperature of the various experimental setups, the corresponding activation energy values were derived and evaluated. Calculated mobilities by TVSE and back-propagation ANN models were compared with each other and to the experimental data, respectively. Neural network approaches were able to model the complex impact of both temperature and organic additive concentrations and resulted in considerably higher predictive power over the TVSE models, justifying that the effect of these two factors should not be neglected. [source] The role of methylnaphthalene in EHV cable oil as related to oil breakdown and discharge velocityEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 6 2002A. Al-Sulaiman This experimental investigation explores the effect of high voltage lightning surges on the insulating oil used in the oil filled extra high voltage cables that serve electric power networks worldwide. Using non-uniform electrode configuration, the breakdown voltage and corresponding discharge propagation velocities in oil samples that are doped with trace amounts of 1-Methylnaphthalene are investigated under both polarities of applied stresses in gap spacing of up to 10 mm. Two distinct ranges of additive concentrations are observed which effect these characteristics. Generally, the positive discharge growth decreases with increase in gap spacing while the negative ones show opposite behaviour. Anomalous behaviour of discharge growth is observed at an optimum concentration of additive, as it attains supersonic velocity which increases with the increase in gap spacing. A correlation between the positive impulse breakdown voltage and the discharge propagation velocity is also established. [source] Polyurethane and sulfonated polysulfone blend ultrafiltration membranes: II.POLYMER INTERNATIONAL, Issue 3 2003Application studies Abstract Ultrafiltration membranes are largely being applied for macromolecular and heavy metal ion separations from aqueous streams. Polyurethane- and sulfonated- polysulfone-based membranes prepared in the absence and presence of the polymeric additive, poly(ethylene glycol) 600, in various compositions, were subjected to the rejection of macromolecular proteins, such as bovine serum albumin, egg albumin, pepsin and trypsin. Toxic heavy metal ions such as Cu2+, Ni2+, Cd2+ and Zn2+ were subjected to rejection by the blend membranes by complexing them with a polymeric ligand, polyethyleneimine. The effects of polymer blend compositions and additive concentrations on the rejection and permeate flux of both proteins and metal ions are discussed. The rejection and permeate flux efficiencies of the blend membranes are compared with pure sulfonated polysulfone membranes. © 2003 Society of Chemical Industry [source] | |||||||||||||