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Retention Data (retention + data)
Selected AbstractsRetention data from reverse-phase high-performance thin-layer chromatography in characterization of some bis-salicylic acid derivativesBIOMEDICAL CHROMATOGRAPHY, Issue 8 2009-Sekuli, Tatjana Djakovi Abstract The chromatographic behaviour of salicylic acid derivatives was investigated using reversed-phase high performance thin-layer chromatography (RP HPTLC) with methanol,water and dioxane,water binary mixtures as mobile phase in order to establish relationships between chromatographic data and selected physico-chemical parameters that are related to ADME (absorption, distribution, metabolism and elimination). Some of the investigated compounds were screened for antioxidant activity. Examination of chromatographic behaviour revealed a linear correlation between RM values and the volume fraction of mobile phase modifier. Obtained RM0 values were correlated with lipophilicity, solubility, human intestinal absorption, plasma-protein binding, and blood,brain barrier data. The comparison among chromatographic data obtained by two mobile phase was performed with a statistical technique, principle component analysis. Copyright © 2009 John Wiley & Sons, Ltd. [source] Linear retention indices in gas chromatographic analysis: a reviewFLAVOUR AND FRAGRANCE JOURNAL, Issue 5 2008Barbara d'Acampora Zellner Abstract The main purpose of any chromatographic analysis is to resolve mixtures of compounds into less complex mixtures or ultimately into pure components. In addition to this function, the chromatographic system can provide retention data which serve as complementary information for the positive identification of resolved components. The need to express gas chromatographic retention data in a standardized system has long been recognized and retention index values presented to be a valuable parameter. Those values are mainly calculated by applying the equations proposed by Kováts, for isothermal analysis, and van den Dool and Kratz, for programmed gas chromatographic runs. In general, these indices denote the retention behaviour of the compounds of interest according to a uniform scale determined by a series of closely related standard substances. The use of retention indices in the flavour and fragrance field is well-documented, and they are widely applied for the comparison of results between laboratories, as well as to characterize stationary phases. Copyright © 2008 John Wiley & Sons, Ltd. [source] Twelve-month Sealant Retention in a School-based Program Using a Self-etching Primer/AdhesiveJOURNAL OF PUBLIC HEALTH DENTISTRY, Issue 4 2004Daniel J. Venker DDS ABSTRACT Objectives: Very little independent research has been done on the new self-etching primer/adhesives in dentistry. A recent clinical study compared two sealant application techniques involving self-etching primer adhesives and the traditional phosphoric acid etch. The purpose of this study was to compare these two techniques in an Iowa school-based sealant program. Methods: Twelvemonth sealant retention data on 208 students from the Des Moines, Iowa, school-based sealant program were analyzed retrospectively. Results: Sealant retention reported at the person level showed that 60 percent of the students who received sealants at the five schools had to be recalled at one year to have one or more surfaces reseated. A logistic regression model at the person level demonstrated that the phosphoric acid technique was six times as likely to have retention of all the sealed tooth surfaces as those sealed with Prompt-L-Pop®. Conclusions: In this study, many students had to be recalled to the chair 12 months after sealant application due to incomplete retention. Though sealants were retained in larger numbers with phosphoric acid, overall sealant retention at the tooth level was lower than previously published for clinical studies and school-based programs. Examining retention data at the person level, however, allows program administrators to plan resources more effectively and reevaluate sealant protocol to ensure as few children return for sealant reapplication. [source] Evaluation of HPLC columns: A study on surface homogeneity of chemically bonded stationary phasesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 3-4 2003Bogus, aw Buszewski Abstract The aim of the current work is to study the heterogeneity of the adsorbent surface on the basis of physicochemical investigations and chromatographic tests. A series of packing materials with octadecyl chains chemically bonded to a silica matrix were prepared for this purpose. The surface and structural properties of bare silica and silica-based octadecyl phases were characterized by porosimetry, elemental analysis, 29Si CP/MAS NMR, etc. The most advanced characterization methods based on adsorption microcalorimetry (heat of wetting) measurements were employed to obtain information about the heterogeneity and topography of unmodified and modified silica gel. For the chromatographic study, these phases were evaluated on the basis of the retention data under non-aqueous conditions. A test series of solutes with various chemical properties, such as pK a values, was used. It was found that heterogeneity of the packing surface results in low HPLC resolution. Use of a non-aqueous mobile phase (n -hexane) reduces analytical interference by eliminating hydrophobic interactions between alkyl ligands and the analyte. [source] Use of Topological Indices of Organic Sulfur Compounds in Quantitative Structure-Retention Relationship StudyMOLECULAR INFORMATICS, Issue 9 2005F. Safa Abstract Structure-gas chromatographic retention index models were developed for some organic sulfur compounds at four different temperatures (60, 80, 100 and 120,°C) using only topological descriptors. At first, regression models were generated for each temperature separately with high values of multiple correlation coefficient and Fisher-ratio statistics. The results of cross validation test using leave-one-out (Q2,0.956) and leave-two-out (Q2,0.953) methods showed good predictive ability of the models developed. Then, a single combined quantitative structure-retention relationship model, added temperature as a parameter, was also developed for all the temperatures, showing good statistical parameters (R=0.991 and F=728.474). The stability and validity of the combined model were verified by both internal (Q2>0.970) and external validation (Q=0.993) techniques. The results of the study indicated the efficiency of the classical topological descriptors in simultaneous prediction of retention index values of sulfur compounds at different temperatures. The topological descriptors well covered the molecular properties known to be relevant for gas chromatographic retention data, such as molecular size and degree of branching. [source] Dietary protein/lipid level and protein source effects on growth, tissue composition and lipid metabolism of blackspot seabream (Pagellus bogaraveo)AQUACULTURE NUTRITION, Issue 2 2010A.C. FIGUEIREDO-SILVA Abstract A study was carried out to determine the effects of fish meal (FM) replacement by plant protein (PP) on growth, body composition and lipid metabolism of blackspot seabream fed different protein/lipid levels. Four experimental diets were formulated to contain two protein (P) and lipid (L) levels (60P/6L or 50P/10L), varying in their protein source (100% FM or 50% FM: 50% PP). Dietary inclusion of PP did not affect growth of fish fed 60P/6L, although fish fed 50P/10L exhibited lower final body weight and daily growth index. Fish fed 60P/6L presented the highest protein and the lowest lipid content. FM replacement by PP has decreased muscle n-3 whereas the n-6 fatty acids increased. Glucose-6-phosphate dehydrogenase and fatty acid synthetase (FAS) were depressed in fish fed 50P/10L. FAS was significantly increased with 60P/6L PP which was positively correlated with lipid retention data. Those results suggest the conversion of other nutrient than lipid (protein and/or carbohydrates) into corporal fat. Hepatic lipoprotein lipase activity was lowest in fish fed PP diets. Plasma glucose peaked 1,2 h postfeeding, in all groups and was generally higher with 60P/6L FM. This work shown that besides dietary P/L level, protein source has a strong effect on species lipogenesis and lipid retention. Hence, the 50P/10L FM diet was the most cost-effective for blackspot seabream juveniles. [source] Optimum histidine requirement of fry African catfish, Clarias gariepinus (Burchell)AQUACULTURE RESEARCH, Issue 9 2009Mukhtar A Khan Abstract Dietary histidine requirement of fry African catfish, Clarias gariepinus (2.57 ± 0.02 cm; 0.22 ± 0.03 g) was quantified by feeding casein,gelatin-based isonitrogenous (40% crude protein) and isocaloric (17.90 kJ g,1 gross energy) amino acid test diets with graded levels of histidine (0.25%, 0.30%, 0.35%, 0.40%, 0.45% and 0.50% dry diet) in eighteen 80 L indoor circular aqua-coloured troughs provided with the flow-through system for 12 weeks. Maximum absolute weight gain (2.66), best feed conversion ratio (1.29), highest protein efficiency ratio (1.94), protein retention efficiency (34%) and energy retention efficiency (70.4%) were achieved at 0.40% dietary histidine. Broken-line and non-linear regression models were adopted to assess dietary histidine requirement for C. gariepinus. When analysed using broken-line regression model these parameters were also best at 0.40% dietary histidine corresponding to 1.0% protein, respectively, whereas using second-degree polynomial regression analysis, histidine requirement was obtained at 0.42%, 0.41%, 0.40%, 0.41% and 0.41% of dry diet, corresponding to 1.05%, 1.02%, 1.0%, 1.02% and 1.02% protein respectively. Based on the broken-line and second-degree polynomial regression analyses of the growth and nutrient retention data, optimum histidine requirement of fry C. gariepinus was found to be in the range of 0.40,0.42% dry diet, corresponding to 1.0,1.05% of dietary protein. [source] Development of predictive quantitative retention,activity relationship models of alkaloids by mixed micellar liquid chromatographyBIOMEDICAL CHROMATOGRAPHY, Issue 2 2010Yu Chen Abstract The mixed micellar liquid chromatography is a mode that uses mixed micellar system of Brij35/SDS (85 : 15) as a mobile phase under adequate experimental conditions, can simulate the resting membrane potential and the conformation of the long hydrophilic polyoxyethylene chains remains unchanged. In this article, the applications of biopartitioning micellar chromatography, using mixed micellar system to describe and estimate bioactivities of alkaloids, has been focused. The BMCBrij35/SDS -QRAR models of half-life time, volume of distribution, plasma clearance and area under concentration,time curve were obtained using Brij35-SDS retention data. The aim is to take a look at the capability of the mixed micellar liquid chromatography model to describe and/or estimate the bioactivity of alkaloids. Copyright © 2009 John Wiley & Sons, Ltd. [source] Data evaluation in chromatography by principal component analysisBIOMEDICAL CHROMATOGRAPHY, Issue 1 2010T. Cserháti Abstract The newest achievements in the employment of principal component analysis, a multivariate mathematical statistical method, in the evaluation of chromatographic retention data are compiled. The results obtained by various chromatographic technologies such as gas,liquid chromatography, thin,layer chromatography, high-performance liquid chromatography and electrically driven systems are compiled and briefly discussed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Investigating the Feasibility of Stem Cell Enrichment Mediated by Immobilized SelectinsBIOTECHNOLOGY PROGRESS, Issue 6 2007Nichola Charles Hematopoietic stem cell therapy is used to treat both malignant and non-malignant diseases, and enrichment of the hematopoietic stem and progenitor cells (HSPCs) has the potential to reduce the likelihood of graft vs host disease or relapse, potentially fatal complications associated with the therapy. Current commercial HSPC isolation technologies rely solely on the CD34 surface marker, and while they have proven to be invaluable, they can be time-consuming with variable recoveries reported. We propose that selectin-mediated enrichment could prove to be a quick and effective method for recovering HSPCs from adult bone marrow (ABM) on the basis of differences in rolling velocities and independently of CD34 expression. Purified CD34+ ABM cells and the unselected CD34, ABM cells were perfused over immobilized P-, E-, and L-selectin-IgG at physiologic wall shear stresses, and rolling velocities and cell retention data were collected. CD34+ ABM cells generally exhibited lower rolling velocities and higher retention than the unselected CD34, ABM cells on all three selectins. For initial CD34+ ABM cell concentrations ranging from 1% to 5%, we predict an increase in purity ranging from 5.2% to 36.1%, depending on the selectin used. Additionally, selectin-mediated cell enrichment is not limited to subsets of cells with inherent differences in rolling velocities. CD34+ KG1a cells and CD34, HL60 cells exhibited nearly identical rolling velocities on immobilized P-selectin-IgG over the entire range of shear stresses studied. However, when anti-CD34 antibody was co-immobilized with the P-selectin-IgG, the rolling velocity of the CD34+ KG1a cells was significantly reduced, making selectin-mediated cell enrichment a feasible option. Optimal cell enrichment in immobilized selectin surfaces can be achieved within 10 min, much faster than most current commercially available systems. [source] | |||||||||||||