Home About us Contact
|
Home About us Contact | ||
|
|
||
Column Temperature (column + temperature)
Selected AbstractsA simplified method for HPLC-MS analysis of sterols in vegetable oilEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 12 2008Antonio Segura Carretero Abstract We have developed a liquid-chromatographic method using atmospheric pressure chemical ionization (APCI)-mass spectrometry (MS) detection in positive mode. This method was used to separate and identify 15,sterols and 2,dihydroxy triterpenes in saponified oils, enabling the analysis of these compounds directly from saponified samples without recourse to thin-layer chromatography; this fact thus significantly simplifies the process. The analyses were made using a Waters Atlantis 5,µm dC18 150×2.1,mm column with a gradient of acetonitrile/water (0.01% acetic acid) at a flow rate of 0.5,mL/min and a column temperature of 30,°C. The quantification of several of these compounds in soybean oil, palm oil, seed oil, sunflower oil, olive-pomace oil and virgin olive oil was carried out using their commercial standards, and the results were compared satisfactorily with the official method. [source] A comparison of forest and moorland stream microclimate, heat exchanges and thermal dynamicsHYDROLOGICAL PROCESSES, Issue 7 2008David M. Hannah Abstract Although the importance of riparian forest in moderating stream temperature variability is recognized, most previous research focuses on conifer harvesting effects and summer maximum temperature with highly variable findings. This article compares stream temperature, microclimate and heat exchange dynamics between semi-natural forest and moorland (no trees) reaches in the Scottish Cairngorms over two calendar years to provide a longer-term perspective. Mean daily water column temperature is warmer for moorland than forest in late winter,early spring, but cooler in summer. Daily water column temperature range is greater for moorland than forest. Streambed temperature dynamics are markedly different between reaches, reflecting contrasting groundwater,surface water (GW,SW) interactions. Mean, minimum and maximum daily air temperature is cooler, humidity is lower, and wind speed is much higher for moorland than forest on average. Net radiation is the dominant heat sink in autumn,winter and major heat source in spring,summer for moorland and summer for forest. Net radiation is greater in summer and lower in winter for moorland than forest. Sensible heat is an energy source in autumn,winter and sink in spring,summer, with loss (gain) greater in summer (winter) for moorland than forest. Latent heat is predominantly a sink for both reaches, with magnitude and variability higher for moorland than forest. Streambed heat flux is much smaller than fluxes at the air,water interface, with moorland and forest illustrating seasonal and between-reach differences attributable to different GW,SW interactions. Seasonal patterns in stream energy budget partitioning are illustrated schematically. To our knowledge, this is the first such study of mixed woodland, which generates notably different results to work on coniferous forest. This research provides a process basis to model stream thermal impact of changes in forest practice, and so inform decision making by land and water resource managers. Copyright © 2008 John Wiley & Sons, Ltd. [source] Lactic acid quantitation in hand dishwashing liquid using an HILIC-UV methodologyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 6-7 2010Mark Storton Abstract Different hydrophilic interaction chromatography (HILIC) columns were screened for lactic acid separation in hand dishwashing liquid products and the influence of mobile phase strength, buffer concentration and column temperature on the retention of lactic acid on a Zorbax NH2 column was investigated. An isocratic HILIC method for the quantitation of lactic acid in hand dishwashing liquid products was developed. The mobile phase consists of 70% methanol and 30% 20,mM sodium phosphate buffer (v/v) at pH 2.5. The HILIC stationary phase is Zorbax NH2, 250×4.6 with a 5,,m particle size. Detection was carried out using a variable wavelength UV-VIS detector at 226,nm. The linear range and percent recovery for lactic acid in the products were 44.68,1206.39,,g/mL and 100.3%, respectively. This paper provides an optimized HILIC methodology for the analysis of an acidic polar analyte (lactic acid) on a basic stationary phase. The proposed method can be used for the routine analysis of lactic acid. [source] Mobile phase additives for enhancing the chromatographic performance of astaxanthin on nonendcapped polymeric C30 -bonded stationary phasesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 1 2009Philipp Kaiser Abstract Astaxanthin shows peak deformation and reduced peak area response when eluted with methanol and methyl tert -butyl ether on nonendcapped polymeric C30 -bonded HPLC phases. The present study tested different column manufacturers, column batches, and ten mobile phase additives including acids, bases, buffers, complexing and antioxidant agents for improvement of peak shape and peak area response. Concerning chromatographic benefits and feasibility, ammonium acetate was found to be the best additive followed by triethylamine for all columns tested. Variation of the mobile phase pH equivalent and the column temperature showed no synergistic effects on peak shape and peak area response. Results indicate that peak tailing and variation of peak area response are due to different on-column effects. Possible mechanisms of the observed phenomenon will be discussed. [source] Evaluation of mobile phase, ion pairing, and temperature influence on an HILIC-MS/MS method for L -arginine and its dimethylated derivatives detectionJOURNAL OF SEPARATION SCIENCE, JSS, Issue 13 2008Giuseppe Paglia Abstract Asymmetric NG,,NG -dimethylarginine (ADMA) increases in diseases such as renal failure, diabetes mellitus, and hypercholesterolemia. The feasibility and utility of a hydrophilic interaction chromatography (HILIC) method for the separation of free L -arginine (Arg), ADMA, and symmetric NG,,NG, -dimethylarginine (SDMA) on a typical silica column were explored and the impact of some experimental parameters on the chromatographic behavior of these analytes was investigated. The effect of water and TFA content in mobile phase and of column temperature was investigated during the development of a fast and simple HILIC-MS/MS method that might be suitable for the quantification of free Arg, ADMA, and SDMA in plasma for routine analysis. Our results show that a good compromise between efficiency and peak shape with acceptable retention and total chromatographic run time is achieved using an ACN/water (90:10) mobile phase with TFA% as additive ranging from 0.015 to 0.025% and column temperature ranging from 25 to 30°C. [source] Effect of temperature on the chromatographic retention of ionizable compounds.JOURNAL OF SEPARATION SCIENCE, JSS, Issue 6-7 2008Abstract We propose a general simple equation for accurately predicting the retention factors of ionizable compounds upon simultaneous changes in mobile phase pH and column temperature at a given hydroorganic solvent composition. Only four independent experiments provide the input data: retention factors measured in two pH buffered mobile phases at extreme acidic and basic pH values (e. g., at least ± 2 pH units far from the analyte pKa) and at two column temperatures. The equations, derived from the basic thermodynamics of the acid,base equilibria, additionally require the knowledge of the solute pKa and enthalpies of acid,base dissociation of both the solute and the buffer components in the hydroorganic solvent mixture. The performance of the predictive model is corroborated with the comparison between theoretical and experimental retention factors of several weak acids and bases of important pharmacological activity, in mobile phases containing different buffer solutions prepared in 25% w/w ACN in water and at several temperatures. [source] Enantioselective HPLC resolution of synthetic intermediates of armodafinil and related substancesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 6-7 2008Ramisetti Nageswara Rao Abstract Armodafinil is a unique psychostimulant recently approved by the US Food and Drug Administration for the treatment of narcolepsy. The chromatographic resolution of its chiral intermediates including related substances in the total synthesis of armodafinil was studied on polysaccharide-based stationary phases, viz. cellulose tris-(3,5-dimethylphenylcarbamate) (Chiralcel OD-H) and amylose tris-(3,5-dimethylphenylcarbamate) (Chiralpak AD-H) by HPLC. The effects of 1-propanol, 2-propanol, ethanol, and trifluoroacetic acid added to the mobile phase and of column temperature on resolution were studied. A good separation was achieved on cellulose-based Chiralcel OD-H column compared to amylose-based Chiralpak AD-H. The effects of structural features of the solutes and solvents on discrimination between the enantiomers were examined. Baseline separation with Rs >1.38 was obtained using a mobile phase containing n -hexane,ethanol,TFA (75:25:0.15 v/v/v). Detection was carried out at 225 nm with photodiode array detector while identification of enantiomers was accomplished by a polarimetric detector connected in series. The method was found to be suitable not only for process development of armodafinil but also for determination of the enantiomeric purity of bulk drugs and pharmaceuticals. [source] Recent developments in the high-performance chelation ion chromatography of trace metalsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 11 2007Pavel N. Nesterenko Abstract There have been a number of significant developments in the high-performance chelation ion chromatography (HPCIC) of trace metals in recent years. This review focuses on these developments, while giving important information on the fundamental parameters controlling the chelation sorption mechanism, including type of chelating group, stability constants, kinetics, and column temperature. The discussion pays particular attention to the types and properties of efficient chelating stationary phases which have been fabricated for certain groups of metals. The review also describes a number of major improvements in postcolumn reaction detection including the use of the latest reagents and noise reduction strategies to improve sensitivity and reduce LOD. In the final section, an indication of the applicability of HPCIC to a range of complex sample types is given with some key examples and chromatograms using the latest high-efficiency chelating phases. [source] The application of small porous particles, high temperatures, and high pressures to generate very high resolution LC and LC/MS separationsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 8 2007Robert Plumb Abstract The effect of combining sub-2 ,m porous particles with elevated operating temperatures on chromatographic performance has been investigated in terms of chromatographic efficiency, productivity, peak elution order, and observed operating pressure. The use of elevated temperature in LC does not increase the obtainable performance but allows the same performance to be obtained in less time. Increasing the column temperature did allow the use of longer columns, generating column efficiencies in excess of 100 000 plates and gradient peak capacities approaching 1000. Raising the temperature increased the optimal mobile phase linear velocity, negating somewhat the pressure benefits observed by reducing the solvent viscosity. When operating at higher temperature the analyte retention is not only reduced, but the order of elution will also often change. High temperature separations allowed exotic organic modifiers such as isopropanol to be exploited for alternative selectivity and faster analysis. Finally, care must be taken when using high temperature separations to ensure that the narrow peak widths produced do not compromise the quality of data obtained from detectors such as high resolution mass spectrometers. [source] HPLC separation of fullerenes on two charge-transfer stationary phasesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 6 2006Qiong-Wei Yu Abstract Two charge-transfer stationary phases were prepared by immobilizing p -nitrobenzoic acid and naphthyl acetic acid onto silica. The nitrophenyl moiety and the naphthyl moiety were grafted to silica gel through the spacer of aminoalkyl silanes. The HPLC separation of C60, C70, and higher fullerenes on the new stationary phases was also studied. The influence of mobile phase and column temperature on the separation of C60 and C70 was examined, respectively. The retentions of C60 and C70 on the two stationary phases increased with decreasing toluene content in the mobile phase or with increasing column temperature. Higher fullerenes can be separated well using toluene as the mobile phase on the stationary phase of p -nitrobenzoic acid-bonded silica. [source] Determination of serotonin, melatonin and metabolites in gastrointestinal tissue using high-performance liquid chromatography with electrochemical detectionBIOMEDICAL CHROMATOGRAPHY, Issue 2 2009Rosanna M. W. Chau Abstract In this paper we show a simple isocratic chromatographic method for the detection of serotonin and its precursors and metabolites from various types of gastrointestinal tissue. The paper measures for the first time basal measurements of melatonin in the gastrointestinal tract, which has recently been shown to be released from the musosal lining of the gut. Tissue samples were stable following sample preparation in either 0.1 m perchloric acid or mobile phase. Analysis was carried out using a mobile phase consisting of 10% acetonitrile,90% acetate acid buffer pH 4.0 with 2 mm decane,sulfonic acid sodium salt at a column temperature of 50°C. Electrochemical detection was utilized at a potential of +850 mV vs Ag/AgCl reference electrode at 10 µA full-scale deflection. The detection limit of 5-HT and melatonin was 241 and 308 nm respectively for a 10 µL injection. As a result of the method optimization, total analysis was reduced to 30 min. Accurate responses of the tissue samples following sample preparation could be obtained following a week after storage at ,80°C. This method is capable of preparing and analysing of samples from all regions of the gastrointestinal tract. Copyright © 2008 John Wiley & Sons, Ltd. [source] Simultaneous quantitation of three major triterpenoid glycosides in Centella asiatica extracts by high performance liquid chromatography with evaporative light scattering detectionBIOMEDICAL CHROMATOGRAPHY, Issue 2 2008Feng-Lun Zhang Abstract A high-performance liquid chromatography method with evaporative light scattering detection was established for simultaneous determination of three major triterpenoid glycosides, i.e. asiaticoside, madecassoside and asiaticoside-B, in Centella asiatica extracts. The optimal chromatographic conditions were achieved on a COSMOSIL 5C18 -MS-II column by constant elution with water (0.01% trifluoroacetic acid, v/v) and acetonitrile (1.0% methyl tert-butyl ether, 0.01% trifluoroacetic acid, v/v) (78:22) as mobile phase at a flow rate of 1.0 mL/min; the column temperature was 30°C. The evaporative light scattering detector was set at an evaporating temperature of 40°C and nitrogen gas pressure of 3.5 bar. The validation of the method included tests of linearity, sensitivity, precision, repeatability, stability and accuracy. All calibration curves showed good linear regression (r2 > 0.9993) within test ranges. The established method showed good precision and accuracy with overall intra-day and inter-day variations of 1.73,3.06 and 3.89%,4.92%, respectively, and overall recoveries of 97.63,99.39% for the three compounds analyzed. The method developed was successfully applied to quantify the main triterpenoid glycosides in Centella asiatica extracts from different companies. Copyright © 2007 John Wiley & Sons, Ltd. [source] Analysis of chemical and metabolic components in traditional Chinese medicinal combined prescription containing Radix Salvia miltiorrhiza and Radix Panax notoginseng by LC-ESI-MS methodsBIOMEDICAL CHROMATOGRAPHY, Issue 8 2007Ying-Jie Wei Abstract High-performance liquid chromatography,electrospray ionization-mass spectrometry (LC-ESI-MS) methods were developed for the analysis of chemical and metabolic components in traditional Chinese medicinal combined prescription containing Radix Salvia miltiorrhiza and Radix Panax notoginseng (commonly known as Fufang Danshen prescription, FDP). The HPLC experiments used a reversed-phase Zorbax C18 column with the column temperature at 30°C and a binary mobile phase system consisting of aqueous formic acid (0.1%, v/v) and acetonitrile using a gradient elution at the flow rate of 1.0 mL/min. The ESI-MS was operated with a single-quadrupole mass spectrometer in both negative and positive ion modes. 36 major chromatographic peaks of FDP, including 14 saponins, 13 phenolic acids and nine diterpenoid quinones were characterized by their MS spectra and in comparison with some of the reference standards. In addition, after oral administration of extraction of FDP, the rat's plasma, urine and feces were also analyzed; 53 metabolic components including 30 original components and 23 transformative components of FDP were detected, and possible metabolic pathways of some components in FDP were given. The analysis of chemical and metabolic components in FDP by HPLC-MS methods could be a useful means of identifying the multi-components of FDP and to hint at their possible metabolic mechanism of action in the body. Copyright © 2007 John Wiley & Sons, Ltd. [source] Liquid chromatographic separation of the enantiomers of ,-amino acids on a ligand exchange chiral stationary phaseBIOMEDICAL CHROMATOGRAPHY, Issue 5 2003Myung Ho Hyun Abstract A liquid chromatographic ligand exchange chiral stationary phase (CSP) derived from (S)-leucinol was applied in the separation of the enantiomers of 12 ,-amino acids. The resolution was quite successful especially for the enantiomers of ,-amino acids containing aromatic functional group in the side chain. The chromatographic resolution behaviors were dependent on the organic modifier and Cu(II) concentration in aqueous mobile phase and the column temperature. Copyright © 2003 John Wiley & Sons, Ltd. [source] Effect of temperature on the chromatographic retention of ionizable compounds.JOURNAL OF SEPARATION SCIENCE, JSS, Issue 6-7 2008Abstract We propose a general simple equation for accurately predicting the retention factors of ionizable compounds upon simultaneous changes in mobile phase pH and column temperature at a given hydroorganic solvent composition. Only four independent experiments provide the input data: retention factors measured in two pH buffered mobile phases at extreme acidic and basic pH values (e. g., at least ± 2 pH units far from the analyte pKa) and at two column temperatures. The equations, derived from the basic thermodynamics of the acid,base equilibria, additionally require the knowledge of the solute pKa and enthalpies of acid,base dissociation of both the solute and the buffer components in the hydroorganic solvent mixture. The performance of the predictive model is corroborated with the comparison between theoretical and experimental retention factors of several weak acids and bases of important pharmacological activity, in mobile phases containing different buffer solutions prepared in 25% w/w ACN in water and at several temperatures. [source] Thermodynamic origin of the chiral recognition of tryptophan on teicoplanin and teicoplanin aglycone stationary phasesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 5 2005Mohamed Haroun Abstract The D-, L-tryptophan binding and the chiral recognition properties of the teicoplanin and teicoplanin aglycone (TAG) chiral stationary phase (CSPs) were compared at various column temperatures. The solute adsorption isotherms (bi-Langmuir model) were determined for both the two CSPs using the perturbation method. It was demonstrated that the sugar units were involved in the reduction of the apparent enantioselectivity through two phenomena: (i) the inhibition of some enantioselective contacts with low-affinity binding regions of the aglycone and (ii) a decrease in the stereoselective properties of the aglycone high-affinity binding pocket. The phenomenon (ii) was governed by both a decrease in the ratio of the enantiomer adsorption constant and a strong reduction of the site accessibility for D- and L-tryptophan. In addition, a temperature effect study was performed to investigate the chiral recognition mechanism at the aglycone high-affinity pocket. An enthalpy-entropy compensation analysis derived from the Grunwald model as well as the comparison with the literature data demonstrated that the enantioselective binding mode was dependent on an interface dehydration process. The change in the enantioselective process observed between the TAG and teicoplanin CSP was characterized by a difference of ca. 2,3 ordered water molecules released from the species interface. [source] Separation of oil and carotenes from palm oil mill effluent by adsorption chromatography with silica based adsorbentASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009A. L. Ahmad Abstract Malaysia is an agricultural country and the major polluting industrial effluents have been from palm oil industry. Palm oil mill effluent (POME) is a liquid waste which causes a significant impact on the environment if it is not dealt properly. POME contains oil and carotenes that need to be treated before discharge. Owing to the readily available source of POME and growing demand of carotenes, the objective of this paper is to recover the carotenes from POME whilst tackling the environmental problem. In this study, solvent extraction is used to retrieve oil from POME and adsorption chromatography is further adopted to recover the carotenes contained in the oil. Residual oil extracted from POME in this study was about 5000 mg/L in a single stage solvent extraction. The carotenes content in recovered oil was about 450 ppm. Synthetic adsorbent with silica based material was used in the adsorption chromatography. Carotenes was concentrated to about 25 times of the concentration in the recovered oil by adsorption chromatography. Carotenes recovery was found to be depended on the process conditions. Different types of solvent, column temperatures and initial loading volumes were evaluated to determine the effects on the percentage of carotenes extracted and carotenes concentration. The suitable temperature for adsorption process was 40 °C. Carotenes was successfully concentrated from the recovered oil by adsorption chromatography process. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | ||||||||||