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Plate Numbers (plate + number)
Selected AbstractsEffects of heterogeneous electron-transfer rate on the resolution of electrophoretic separations based on microfluidics with end-column electrochemical detectionELECTROPHORESIS, Issue 19 2009Joseph Wang Abstract We demonstrate here that the electrode kinetics of an electrochemical detector contributes greatly to the resolution of the analyte bands in microchip electrophoresis systems with amperometric detection. The separation performance in terms of resolution and theoretical plate number can be improved and tailored by selecting or modifying the working electrode and/or by controlling the detection potential. Such improvements in the separation performance reflect the influence of the heterogeneous electron-transfer rate of electroactive analytes upon the post-channel band broadening, as illustrated for catechol and hydrazine compounds. The electrode kinetics thus has a profound effect not only on the sensitivity of electrochemical detectors but on the separation efficiency and the overall performance of microchip electrochemistry systems. [source] Organic solvents in CEELECTROPHORESIS, Issue S1 2009Ernst Kenndler Abstract In this contribution some fundamental aspects are discussed serving for a critical reflection and elucidation of the role of organic solvents in CE. The implications of the solvent on the parameters governing peak resolution are discussed based on the concepts describing migration and zone broadening in capillary zone electrophoresis. This discussion includes the solvent-dependent influence of the ionic strength on the mobility. The role of the solvent on the plate number in case of the inevitable diffusional peak dispersion is outlined, and its effect on other peak broadening contributions is briefly examined. This paper also deals with the problems of conductance, applicable voltage and analysis time upon application of organic solvents, and tries to clarify some misunderstandings common in the literature. [source] In vivo ultra-high-field magnetic resonance imaging of trabecular bone microarchitecture at 7 TJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2008Roland Krug PhD Abstract Purpose To investigate the feasibility of 7T magnetic resonance imaging (MRI) to visualize and quantify trabecular bone structure in vivo by comparison with 3T MRI and in vivo three-dimensional (3D) high-resolution peripheral quantitative computed tomography (HR-pQCT). Materials and Methods The distal tibiae of 10 healthy volunteers were imaged. Therefore, fully balanced steady state free precession (bSSFP) and spin-echo (bSSSE) pulse sequences were implemented and optimized for 7T. Structural bone parameters, such as apparent bone-volume over total-volume fraction (app.BV/TV), apparent trabecular plate separation (app.TbSp), apparent trabecular plate thickness (app.TbTh), and apparent trabecular plate number (app.TbN), were derived. Results All structural trabecular bone parameters correlated well (r > 0.6) between 7T and 3T, and between 7T and HR-pQCT (r > 0.69), with the exception of app.TbTh, which correlated modestly (r = 0.41) between field strengths and very low with HR-pQCT (r < 0.16). Regarding absolute values, app.TbN varied only 4% between field strengths, and only 0.6% between 7T and HR-pQCT. App.TbSp correlated best between 7T and HR-pQCT (r = 0.89). Using bSSSE, significant smaller trabecular thickness and significant higher trabecular number were found compared to bSSFP. Conclusion We concluded that imaging and quantification of the trabecular bone architecture at 7T is feasible and preferably done using bSSSE. There exists great potential for ultra-high-field (UHF) MRI applied to trabecular bone measurements. J. Magn. Reson. Imaging 2008;27:854,859. © 2008 Wiley-Liss, Inc. [source] Hydrophilic interaction LC of peptides: Columns comparison and clusteringJOURNAL OF SEPARATION SCIENCE, JSS, Issue 6-7 2010Sylvia Van Dorpe Abstract A wide variety of hydrophilic interaction chromatography (HILIC) stationary phase surface chemistries are currently available. Although their selectivity can be considerably different, column comparison or clustering using peptides is limited. In this study, ten pharmaceutically relevant model peptides are analyzed on seven different HILIC columns (bare silica, amide, poly-hydroxyethyl aspartamide, diol and zwitterionic) for the evaluation of their performance and classification. The responses examined include single and multiple responses: plate number, asymmetry factor, LOD, geometric mean resolution, resolution product, time corrected resolution product, peak capacity and chromatographic response function. Column classification was performed using hierarchical clustering and principal component analysis. Moreover, the overall performance quality of the HILIC columns was compared using a linear desirability function. Hierarchical clustering and principal component analysis showed consistent clusters. The zwitterionic phase was clustered apart from the other HILIC columns and both poly-aspartamide columns were clustered together. In addition, the two bare silica phases represent two different clusters, and thus different selectivities. Overall, the responses showed the best performance for one of the bare silica columns (Alltima-Alltech), followed by the zwitterionic phase (ZIC)-HILIC. Thus, these columns, belonging to different clusters, were found to be the best performing systems in pharmaceutical peptide analysis for the selected peptide set. [source] Separation of benzene and deuterated benzenes by reversed-phase and recycle liquid chromatography using monolithic capillary columnsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 15-16 2004Lee Wah Lim Abstract An alternate pumping-recycle system utilizing a commercially available low dead-volume switching valve was developed for microcolumn LC. The recycle system had two separation columns, and the dead volume of the recycling lines was kept to a minimum by avoiding passage of the sample through the pump chamber, sample injector, and the normal path length of a conventional UV detector. The drawback of the high total back pressure caused by the second column that is placed after the detector was overcome by on-column detection, and this eliminated the need for a high pressure flow cell. The system was used for the separation of an authentic mixture of benzene, benzene-1,3,5-d3, and benzene-d6. Baseline separation was accomplished after six cycles and the calculated theoretical plate number for benzene was 230,000. It was observed that the theoretical plate number (N) increased linearly with increasing number of cycles, and the N per unit time increased with increasing inlet pressure. The separation conditions were optimized and the separation of benzene and benzene-d6 was accomplished within 75 min at 2.5 MPa inlet pressure. [source] Evaluation of CE methods for global metabolic profiling of urineELECTROPHORESIS, Issue 14 2010Rawi Ramautar Abstract In this study, the usefulness of noncovalently coated capillaries with layers of charged polymers is investigated to obtain global electrophoretic profiles of urinary metabolites covering a broad range of different compound classes in a highly repeatable way. Capillaries were coated with a bilayer of polybrene (PB) and poly(vinyl sulfonate) (PVS), or with a triple layer of PB, dextran sulfate (DS) and PB. The bilayer and triple layer coatings were evaluated at acidic (pH 2.0) and alkaline (pH 9.0) separation conditions, thereby providing separation conditions for basic and acidic compounds. A representative metabolite mixture and spiked urine samples were used for the evaluation of the four CE methods. Migration time repeatability (RSD<2%) and plate numbers (N, 100,000,400,000) were similar for the test compounds in all CE methods, except for some multivalent ions that may exhibit adsorption to oppositely charged coatings. The analysis of cationic compounds with the PB-DS-PB CE method at low pH (i.e. after the EOF time) provided a larger separation window and number of separated peaks in urine compared to the analysis with the PB-PVS CE method at low pH (i.e. before the EOF time). Approximately, 600 molecular features were detected in rat urine by the PB-DS-PB CE-MS method whereas about 300 features were found with the PB-PVS CE-MS method. This difference can be attributed to reduced comigration of compounds with the PB-DS-PB CE-MS method and a related decrease of ion suppression. With regard to the analysis of anionic compounds by CE-MS, in general analyte responses were significantly lower than that for cationic compounds, most probably due to less efficient ionization and to ion suppression effects caused by the background electrolyte. Hence, further optimization is required for the sensitive CE-MS analysis of anionic compounds in body fluids. It is concluded that the selection of a CE method for profiling of cationic metabolites in urine depends on the purpose of the study. For high-throughput analyses, the PB-PVS CE-MS method is favored whereas the PB-DS-PB CE-MS method provides a more information-rich metabolic profile, but at the cost of prolonged analysis time. [source] Capillary electrophoretic separation of biologically active amines and acids using nanoparticle-coated capillariesELECTROPHORESIS, Issue 9 2008Yu-Fen Huang Abstract This manuscript describes dynamic coating of capillaries with poly(L -lysine) (PLL) and silica nanoparticles (SiO2 NPs) and use of the as-prepared capillaries for the separation of biogenic amines and acids by CE in conjunction with LIF detection. The directions of EOF are controlled by varying the outmost layer of the capillaries with PLL and SiO2 NPs, respectively. Over the pH range 3.0,5.0, the (PLL,SiO2NP)n,PLL capillaries have an EOF toward the anodic end and are more suitable for the separation of acids with respect to speed, while the (PLL,SiO2NP)n capillaries have an EOF toward the cathodic end and are more suitable for the separation of biogenic amines regarding speed and sensitivity. The separations of standard solutions containing five amines and two acids by CE with LIF detection using (PLL,SiO2NP)2,PLL and (PLL,SiO2NP)3 capillaries were accomplished within 10 and 7,min, providing plate numbers of 3.8 and 5.0×104,plates/m for 5-hydroxytryptamine (5-HT), respectively. The LODs for 5-HT and 5-hydroxyindole-3-acetic acid (5-HIAA) are 32 and 2,nM and 0.2 and 1.5,nM when using the (PLL,SiO2NP)2,PLL and (PLL,SiO2NP)3 capillaries, respectively. Identification and quantification of 5-HIAA, homovanillic acid, and DL -vanillomandelic acid in urine samples from a male before and after drinking green tea were tested to validate practicality of the present approach. The results show that the (PLL,SiO2NP)2,PLL capillary provides greater resolving power, while the (PLL,SiO2NP)3 capillary provides better sensitivity, higher efficiency, and longer durability for the separation of the amines and acids. [source] Effect of detergent on electromigration of proteins: CE of very low density lipoprotein receptor modules and viral proteinsELECTROPHORESIS, Issue 20 2007Leopold Kremser Dr. Abstract The different electrophoretic behavior of the members of two groups of proteins with respect to the absence or presence of detergent additives in the BGE was explored. Recombinant soluble concatemers of repeat 3 of the very low density lipoprotein (VLDL)-receptor fused at their N -terminus to maltose-binding protein (MBP) exhibited different electrophoretic mobilities in borate buffer (pH,8.3) in the absence and in the presence of dodecyl-PEG ether (D-PEG). This enabled the separation of the receptor fragments from MBP after enzymatic cleavage. In the presence of SDS, the mobilities of all proteins approached the same values with increase in detergent concentrations. In contrast, viral capsid proteins of a human rhinovirus (HRV) exhibited different migration in the presence of the additive. For the receptor proteins, extreme apparent high plate numbers were observed when the SDS concentration in the sample and the separation buffer differed. This effect might be erroneously interpreted as a high efficiency. However, it is due to the conductivity boundaries caused by the sample and leads to a total loss of separation. [source] Application of polymeric surfactants in micellar electrokinetic chromatography-electrospray ionization mass spectrometry of benzodiazepines and benzoxazocine chiral drugsELECTROPHORESIS, Issue 5-6 2006Jingguo Hou Abstract Chiral micellar EKC (CMEKC) coupled to ESI-MS using polymeric surfactants as pseudostationary phases is investigated for simultaneous enantioseparation of two benzodiazepines, (±)-oxazepam ((±)-OXA) and (±)-lorazepam ((±)-LOR), and one benzoxazocine, (±)-nefopam ((±)-NEF). First, enantioselectivity and electrospray sensitivity of six chiral polymeric surfactants for all three chiral compounds are compared. Second, using poly(sodium N -undecenoyl- L -leucinate) as pseudostationary phase, the organic modifiers (methanol (MeOH), isopropanol, and ACN) are added into the running buffer to further improve chiral resolution (RS). Next, a CMEKC-ESI-MS method for the simultaneous enantioseparation of two benzodiazepines is further developed by using a dipeptide polymeric surfactant, poly(sodium N -undecenoxy carbonyl- L,L -leucyl-valinate) (poly- L,L -SUCLV). The CMEKC conditions including nebulizer pressure, capillary length, ammonium acetate concentration, pH, poly- L,L -SUCLV concentration, and capillary temperature were optimized to achieve maximum chiral RS and highest sensitivity of MS detection. The spray chamber parameters (drying gas temperature and drying gas flow rate) as well as sheath liquid conditions (MeOH content, pH, flow rate, and ionic strength) were found to significantly influence MS S/N of both (±)-OXA and (±)-LOR. Finally, a comparative study between simultaneous UV and MS detection showed high plate numbers, better chiral RS, and enhanced detectability with CMEKC-MS. However, speed of analysis was faster using CMEKC-UV. [source] ASYMMETRY IN STRUCTURAL DEFENSES: INSIGHTS INTO SELECTIVE PREDATION IN THE WILDEVOLUTION, Issue 9 2003C. A. Bergstrom Abstract Assessment of geographical patterns in fluctuating asymmetry (small, random differences between sides of bilateral characters) among populations shows promise as a tool to resolve the relative biomechanical importance of traits, in addition to being a possible indicator of habitat quality. We used 115 endemic freshwater populations of threespine stickleback (Gasterosteus aculeatus) from Haida Gwaii (Queen Charlotte Islands), British Columbia, Canada, to explore the degree of concordance between geographical variation of asymmetry in a predator defense structure (bony lateral plates) and geographical variation in several indirect measures of predation regime as well as several abiotic habitat variables. We found a geographical cline in the population frequency of lateral plate asymmetries, with reduced asymmetry in the southern clear-water regions of the archipelago characterized by long reaction distances and greater chance of capture by predators, and elevated asymmetry in the northern stained-water regions with poor visibility and low chances of capture. Lateral plate asymmetry was strongly correlated with expression of several defensive armor traits, including total plate numbers among populations, mean cross-sectional diameter of stickleback with the dorsal and pelvic spines erect, and mean degree of overlap between the plates and spine supports. There were no significant correlations between frequency of asymmetric fish and any of our abiotic habitat variables. Stickleback with structural plate asymmetries had fewer trout-induced scars than symmetric fish in the significant majority of populations, and there was a decrease in structural plate asymmetry with age in stained-water habitats, suggesting that trout predators may be selectively removing asymmetric fish in some lakes. This study provides evidence that geographical variation in developmental stability of threespine stickleback, as seen in the frequencies of asymmetry, reflects differences among populations in the importance of structural defenses to fitness rather than differences in habitat quality, and that asymmetry may be a target of selection by predators in wild populations. [source] Fluid flow and heat transfer of natural convection around array of vertical heated platesHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 2 2009Kenzo Kitamura Abstract Natural convective flows around an array of vertical heated plates were investigated experimentally. Main concerns were directed to the influences of plate numbers on the heat transfer characteristics of the plates. Both surfaces of the test plates were heated with constant and equal heat fluxes and their local heat transfer coefficients were measured. The results showed that the coefficients of the surfaces of the array facing outward became higher than those facing inward. The flow fields around the bottom of the plate array were visualized with smoke. The result showed that the ambient flow is directed from the sides to the center of the array and enters the parallel channel obliquely. These flows cause the above difference in the coefficients. While the difference gradually diminished in between the plates placed in the central section of the array, their coefficients asymptotically approach those of the analytical correlation that assumed a uniform velocity at the channel inlet. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20232 [source] ULTRASTRUCTURE AND LSU rDNA,BASED REVISION OF PERIDINIUM GROUP PALATINUM (DINOPHYCEAE) WITH THE DESCRIPTION OF PALATINUS GEN.JOURNAL OF PHYCOLOGY, Issue 5 2009The name Peridinium palatinum Lauterborn currently designates a freshwater peridinioid with 13 epithecal and six cingular plates, and no apical pore complex. Freshwater dinoflagellate floras classify it in Peridinium group palatinum together with P. pseudolaeve M. Lefèvre. General ultrastructure, flagellar apparatus, and pusular components of P. palatinum were examined by serial section TEM and compared to P. cinctum (O. F. Müll.) Ehrenb. and Peridiniopsis borgei Lemmerm., respectively, types of Peridinium and Peridiniopsis. Partial LSU rDNA sequences from P. palatinum, P. pseudolaeve and several peridinioids, woloszynskioids, gymnodinioids, and other dinoflagellates were used for a phylogenetic analysis. General morphology and tabulation of taxa in group palatinum were characterized by SEM. Differences in plate numbers, affecting both the epitheca and the cingulum, combine with differences in plate ornamentation and a suite of internal cell features to suggest a generic-level distinction between Peridinium group palatinum and typical Peridinium. The branching pattern of the phylogenetic tree is compatible with this conclusion, although with low support from bootstrap values and posterior probabilities, as are sequence divergences estimated between species in group palatinum, and typical Peridinium and Peridiniopsis. Palatinus nov. gen. is proposed with the new combinations Palatinus apiculatus nov. comb. (type species; syn. Peridinium palatinum), P. apiculatus var. laevis nov. comb., and P. pseudolaevis nov. comb. Distinctive characters for Palatinus include a smooth or slightly granulate, but not areolate, plate surface, a large central pyrenoid penetrated by cytoplasmic channels and radiating into chloroplast lobes, and the presence of a peduncle-homologous microtubular strand. Palatinus cells exit the theca through the antapical-postcingular area. [source] Capillary electrophoresis of intact basic proteins using noncovalently triple-layer coated capillariesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 14 2009Rob Haselberg Abstract The usefulness of a noncovalent, positively charged capillary coating for the efficient analysis of intact basic proteins with CE was studied. Capillaries were coated by subsequent flushing with solutions of 10% w/v Polybrene (PB), 3% w/v dextran sulfate (DS), and again 10% w/v PB. Coating characterization studies showed that stable coatings could be produced which exhibited a pH-independent and highly reproducible EOF. The PB,DS,PB coating was evaluated with Tris phosphate BGEs of various pH using the four basic model proteins: ,-chymotrypsinogen A, ribonuclease A, cytochrome c, and lysozyme. Typical migration time RSDs for the proteins were less than 0.85%, and apparent plate numbers were above 125 000 using a capillary length of 40 cm. The high separation efficiency allowed detection of several minor impurities in the model proteins. Using a BGE of medium pH, the CE system with triple-layer coating appeared to be useful for the repeatable profiling of recombinant humanized mouse monoclonal immunoglobulin G1 showing a characteristic pattern of glycoforms. The CE system was also applied to the characterization of two llama antibodies, which were produced in Saccharomyces cerevisiae, revealing the presence of a side product in one of the antibodies. The high migration time stability allowed the reliable determination of antibody,antigen binding by monitoring migration time shifts. Finally, the feasibility of using the PB,DS,PB coated capillaries for CE with mass spectrometric detection was shown by the characterization of the impure llama antibody sample. [source] | ||||||||||