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Linear Gradient (linear + gradient)
Terms modified by Linear Gradient Selected AbstractsTechnical Approach to Simplify the Purification Method and Characterization of Microbial Transglutaminase Produced from Streptoverticillium ladakanumJOURNAL OF FOOD SCIENCE, Issue 1 2000M.-L. Ho ABSTRACT: In order to fast and economically purify MTGase from Streptoverticillium ladakanum, a stepwise elution method was developed and compared with linear gradient elution method. MTGase was purified to electrophoretical homogeneity by using CM Sepharose CL-6B and Blue Sepharose Fast Flow chromatographies by linear gradient or stepwise methods. The recovery of MTGase by linear gradient and stepwise methods were 68.4% and 81.0%, respectively. The optimal temperature and pH were 40 °C and 5.5, respectively. It was stable at pH 5.0 to 7.0 and had a rate constant (KD) of 6.21 °o 10 -5 min -1 for thermal inactivation at 45 °C. The purified MTGase was activated by K+ Na+, Ca2+, Mn2+, and Mg2+, not affected by Fe3+, EDTA, but inhibited by Cu2+, Zn2+, Hg2+, Ni2+, Co2+, Cd2+, PCMB, NEM, IAA, and PMSF. A simple stepwise method was developed for the purification of MTGase from S. ladakanum. [source] Semibatch RAFT polymerization for producing ST/BA copolymers with controlled gradient composition profilesAICHE JOURNAL, Issue 4 2008Xiaoying Sun Abstract With controlled/living radical copolymerization, the composition profile along polymer chains becomes a tunable parameter in preparing copolymer products for novel materials properties. In this work, a novel series of styrene/butyl acrylate (St/BA) copolymers with precisely designed composition profiles (uniform, linear gradient, tanh gradient, and triblock with a linear gradient mid-block) were produced using a semibatch reversible addition-fragmentation chain transfer copolymerization mediated by benzyl dithioisobutyrate. The comonomer feeding rate was programmed based on a kinetic model with the targeted composition profile as an objective functions. The experimental composition and molecular weight profiles agreed very well with the model predictions. The polymer molecular weight distributions were narrow with polydispersity index values about 1.3. The amount of dead chains was controlled below 10%. The glass transition behaviors of the St/BA copolymers were evaluated and their Tg values were found to be in an order of uniform < linear gradient < tanh gradient < triblock with 10°C for uniform and 140°C for triblock copolymers. © 2008 American Institute of Chemical Engineers AIChE J 2008 [source] High-performance liquid chromatography determination of hydrastine and berberine in dietary supplements containing goldensealJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2001Ehab A. Abourashed Abstract Goldenseal (Hydrastis canadensis L., Ranunculaceae) is an ingredient of various dietary supplements intended for enhancing general body immunity. Many goldenseal products are currently available in the United States, either alone or in combination with echinacea. In most products, the content of the main active alkaloids of goldenseal, hydrastine and berberine, is not indicated on the label. A high-performance liquid chromatography (HPLC) method has been developed for the detection and quantification of hydrastine and berberine in a number of products obtained from the United States market. The method uses a Phenomenex® Luna C18 column, a mobile phase consisting of solvent A (100 mM sodium acetate/acetic acid, pH 4.0) and solvent B (acetonitrile/methanol; 90/10, v/v). Elution was run at a flow rate of 1.0 mL/min, with a linear gradient of 80, 40% A in B over 20 min and ultraviolet detection at 290 nm. A wide range of content variation was observed for both alkaloids in the tested samples. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:817,822, 2001 [source] Extraction of pure lycopene from industrial tomato by-products in water using a new high-pressure processJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 14 2008Daniele Naviglio Abstract BACKGROUND: Lycopene, a precursor of ,-carotene with a well-known antioxidant activity, contained in many natural products such as tomato (Lycopersicon esculentum Mill.), watermelon, red pepper and papaya, is usually recovered from natural vegetal sources using organic solvents and a purification step. In this paper an innovative process for the extraction of pure lycopene from tomato waste in water that uses the Naviglio® extractor and water as extracting phase is presented. RESULTS: Lycopene was obtained in the all- trans form at a very high grade of purity, not less than 98% (w/w), with an average recovery of 14% (w/w). The availability of high-purity trans -lycopene allowed measurement of the molar absorption coefficient. An alternative procedure for high-performance liquid chromatographic analysis using a phenyl-hexyl silicone phase as inverse phase and a linear gradient in water and acetonitrile is also described. CONCLUSIONS: The use of water as extracting phase considerably reduces the cost of the entire process when compared with the commonly used solvent-based procedure or with the newer supercritical extraction process of lycopene from tomato waste. Lycopene, not soluble in water, was recovered in a quasi-crystalline solid form and purified by solid-phase extraction using a small amount of organic solvent. Copyright © 2008 Society of Chemical Industry This article was published online on September 15, 2008. Errors in Figures 2 - 4 were subsequently identified. The publishers wish to apologise for these errors. This notice is included in the online and print versions to indicate that both have been corrected [September 19, 2008] [source] Analysis of pharmaceutical samples of Resina Draconis by HPLC-PADPHYTOCHEMICAL ANALYSIS, Issue 6 2008Wenjun Gong Abstract Introduction: The quality evaluation of traditional Chinese medicine (TCM) represents a particular challenge owing to the complexity of the matrix, which renders separation and identification of the individual components extremely difficult. In recent years, fingerprinting of TCMs has played a dominant role in quality control. Resina Draconis was authorised as a new TCM in 1991, but a satisfactory HPLC fingerprint method for this preparation has not yet been published. Objective: To develop a simple and reliable protocol for the quality control of Resina Draconis using an HPLC-PAD method. Methodology: The TCM was extracted with methanol at room temperature. Chromatography was carried out using a Lichrospher C18 column eluted with a linear gradient of acetonitrile (A) and water containing 0.1% phosphoric acid (B), initially at 30:70 (A:B) and changing to 60:40 in 90 min. UV (PAD) spectra were acquired in the range 210,400 nm. Results: Four chromatograms of samples of Resina Draconis obtained from different pharmaceutical factories showed 20 peaks in common. The average chromatogram was taken as a template from which the correlation coefficients and cosine ratios of the samples were determined. Whereas the contents of individual components in each sample were different, overall the samples were extremely similar one to another, and the products from different pharmaceutical factories were consistent. Conclusion: A reliable and validated HPLC method has been developed for the fingerprint analysis of Resina Draconis that can be applied for the quality control of this TCM. Copyright © 2008 John Wiley & Sons, Ltd. [source] Isolation and Characterisation of Procyanidins from Rumex obtusifoliusPHYTOCHEMICAL ANALYSIS, Issue 3 2007Paul Spencer Abstract An acetone:water (7:3) extract obtained from the leaves of Rumex obtusifolius was fractionated into procyanidin oligomer and polymer fractions using a linear gradient and a simple step method on Sephadex LH-20. The chemical characteristics of the procyanidin fractions were studied by 13C-NMR spectroscopy, acid-catalysed degradation in the presence of benzyl mercaptan, matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) MS and electrospray ionisation (ESI) MS. The 13C-NMR showed that the polymer fraction consisted predominantly of procyanidin polymers, some with galloyl groups attached. The thiolysis reaction products indicated a mean degree of polymerisation (DP) of 4.3 for the step method, and a range of 2.3,8.2 mean DP for the gradient fractionation, with epicatechin as the most abundant flavan-3-ol extension unit, while the terminal units consisted of equal proportions of catechin, epicatechin and epicatechin gallate. Singly charged ions observed in MALDI-TOF/MS showed a range of oligomeric procyanidins and their polygalloyl derivatives. These species (in the range DP 2,7) were also observed by ESI/MS but the spectra were more complex due to overlapping multiply charged ions. Isolation of oligomers from the Sephadex LH-20 fraction by chromatography on polyamide and C18 yielded B1, B2, B3 and B7 dimers, an A-type trimer and a B2 3,3,- O -digallate. Copyright © 2007 John Wiley & Sons, Ltd. [source] Fractionation of grape tannins and analysis by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometryPHYTOCHEMICAL ANALYSIS, Issue 4 2003Camille Perret Abstract Polymeric tannins, extracted from grape berries (Gamay variety), were fractionated according to their mean degree of polymerisation (mDP) on a styrene,divinylbenzene phase eluted with a gradient of methanol:chloroform. Increasing the percentage of methanol led to the solubilisation of higher molecular weight tannins. The mean mDP of each collected fraction was determined by acid-catalysed degradation in the presence of a nucleophilic reagent. The fractionation method produced a linear gradient of mDP varying between 1.84 and 19.34. The fractions were partially characterised by matrix assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF/MS). The spectra showed a complex mixture of proanthocyanidins and galloylated proanthocyanidins up to 4000,amu. Copyright © 2003 John Wiley & Sons, Ltd. [source] Preparation of a super-long two column chromatography system and its application in separating glycosylated puerarinBIOMEDICAL CHROMATOGRAPHY, Issue 12 2009Shouchuang Zhu Abstract Separation of Puerarin-7- O -glucoside from its precursor, puerarin, using a common chromatography column packed with AB-8 macroporous resin was unsuccessful. Therefore, in this study a 8,m super-long flexible reinforced PVC column was externally added to the common column in order to improve the chromatography efficiency by increasing the number of theoretical plates. Both the PVC and common columns were separately packed with AB-8 macroporous resin slurry. The packed PVC column was coiled after washing and stored until use. The microbial transformation mixture with puerarin-7- O -glucoside and puerarin (250,mL) was loaded onto the common column, followed by washing with 2000,mL H2O. After attaching the coiled external PVC column to the common column, a linear gradient of 10,30% ethanol was applied to elute the target compound. Two peaks appeared: peak I contained puerarin-7- O -glucoside at 97.9% purity and 88.1% recovery rate, and peak II was puerarin at 98.7% purity and 87.0% recovery rate. The use of the coiled external flexible reinforced PVC column avoided spatial restriction for long columns, which made it much more convenient for column packing and chromatography operations. Furthermore, this method eliminated the resin blockage problem caused by stationary water pressure in a rigid vertical long column. Using an external super-long column, the PVC tube was connected with the common column only during elution, which avoided delay in time period during sample loading and column washes associated with the use of long external columns. Copyright © 2009 John Wiley & Sons, Ltd. [source] High performance liquid chromatographic method for the determination and pharmacokinetic studies of oxyresveratrol and resveratrol in rat plasma after oral administration of Smilax china extractBIOMEDICAL CHROMATOGRAPHY, Issue 4 2008Huilian Huang Abstract A sensitive and simple HPLC method has been developed and validated for the determination of oxyresveratrol (trans -2,4,3,,5,-tetrahydroxystilbene, OXY) and resveratrol (trans -3,5,4,-trihydroxystilbene, RES) in rat plasma. The plasma samples were extracted with ethyl acetate and analyzed using HPLC on an Aglient Zorbax SB-C18 column (250 × 4.6 mm, 5 µm) at a wavelength 320 nm, with a linear gradient of (A) acetonitrile and (B) 0.5% aqueous acetic acid (v/v), at a flow rate of 1.0 mL/min. The method was linear over the range of 0.1265,25.3 µg/mL for OXY and 0.117,23.4 µg/mL for RES. The extraction recovery for OXY, RES and internal standard ranged from 71.1 to 88.3%. The intra- and inter-day precisions were better than 10%, and the accuracy ranged from 89 to 108%. The validated method was used to study the pharmacokinetic profiles of OXY and RES in rat plasma after oral administration of Smilax china root extract. Copyright © 2007 John Wiley & Sons, Ltd. [source] The effect of stationary phase on lipophilicity determination of , -blockers using reverse-phase chromatographic systemsBIOMEDICAL CHROMATOGRAPHY, Issue 10 2005Tomasz Welerowicz Abstract Evaluation of lipophilicity parameters for basic compounds using different chromatographic stationary phases is presented. An HPLC method for determination of lipophilic molecule,stationary phase interactions was based on gradient analysis. Differences in correlation between the lipophilicity of compounds and experimental chromatographic results obtained in pseudo-membrane systems showed a strong influence of stationary phase structure and physico-chemical properties. , -Blocker drugs with varying lipophilicity and bio-activity were chosen as test compounds. The stationary phases used for the study were monolithic rod-structure C18 and silica gel octadecyl phase SG-C18 as reference material. The second group was silica gel-based polar-embedded alkylamide and cholesterolic phases. The mobile phase was composed of acetonitrile or methanol with ammonium acetate, and a linear gradient of methanol and acetonitrile in mobile phase was performed. A linear correlation of plots of log kg = f(log P) was observed, especially for polar-embedded phases, and this allowed log PHPLC to be calculated. The behavior of stationary phases in methanol and acetonitrile buffer showed differences between obtained log PHPLC values. Copyright © 2005 John Wiley & Sons, Ltd. [source] Direct characterization of aqueous extract of Hibiscus sabdariffa using HPLC with diode array detection coupled to ESI and ion trap MSJOURNAL OF SEPARATION SCIENCE, JSS, Issue 20 2009Inmaculada C. Rodríguez-Medina Abstract The phenolic fraction and other polar compounds of the Hibiscus sabdariffa were separated and identified by HPLC with diode array detection coupled to electrospray TOF and IT tandem MS (DAD-HPLC-ESI-TOF-MS and IT-MS). The H. sabdariffa aqueous extract was filtered and directly injected into the LC system. The analysis of the compounds was carried out by RP HPLC coupled to DAD and TOF-MS in order to obtain molecular formula and exact mass. Posterior analyses with IT-MS were performed and the fragmentation pattern and confirmation of the structures were achieved. The H. sabdariffa samples were successfully analyzed in positive and negative ionization modes with two optimized linear gradients. In positive mode, the two most representative anthocyanins and other compounds were identified whereas the phenolic fraction, hydroxycitric acid and its lactone were identified using the negative ionization mode. [source] | ||||||||||