Band Broadening (band + broadening)

Distribution by Scientific Domains


Selected Abstracts


Passive broadband reflector using photocrosslinkable liquid crystal molecules

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2002
P. Sixou
Abstract This work consists in creating passive optical filter reflecting light in a broadband wavelength with photo-polymerizable mesogenic liquid crystal (LC) molecules from a reproducable method. The influence of several parameters was studied and it appears that reflective wavelength range can be modified by chiral agent concentration and/or temperature. Band broadening is influenced by several process parameters such as layer thickness, polymerization and dissolution times. A semi-quantitative analysis allows the variation of conversion ratio as a function of polymerization and dissolution times to be determined. Copyright 2002 John Wiley & Sons, Ltd. [source]


Microchip isoelectric focusing with monolithic immobilized pH gradient materials for proteins separation

ELECTROPHORESIS, Issue 23 2009
Yu Liang
Abstract Monolithic immobilized pH gradient (M-IPG) materials were prepared in microchannles by photoinitiated polymerization of acrylamide, glycidylmethacrylate and Bis, followed by the attachment of focused Ampholine onto the surface of porous monoliths via epoxide groups. With M-IPG materials as matrix, FITC-labeled ribonuclease B, myoglobin and ,-casein were well separated by microchip isoelectric focusing (,CIEF) without carrier amphocytes (CAs) added in the buffer. Both chemical and pressure mobilization were applied to drive focused zones for LIF detection. Our experimental results showed that pressure mobilization was preferable with neglectable band broadening, and good peak shape and high detection sensitivity were obtained. All these results demonstrate that ,CIEF with M-IPG materials is not only an efficient mode for protein enrichment and separation but also attractive to couple with other CE modes to achieve multi-dimensional separation or MS for further identification, without the interference of mobile CAs. [source]


Effects of heterogeneous electron-transfer rate on the resolution of electrophoretic separations based on microfluidics with end-column electrochemical detection

ELECTROPHORESIS, Issue 19 2009
Joseph 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]


Nanostructured pillars based on vertically aligned carbon nanotubes as the stationary phase in micro-CEC

ELECTROPHORESIS, Issue 12 2009
Ren-Guei Wu
Abstract We present a micro-CEC chip carrying out a highly efficient separation of dsDNA fragments through vertically aligned multi-wall carbon nanotubes (MWCNTs) in a microchannel. The vertically aligned MWCNTs were grown directly in the microchannel to form straight nanopillar arrays as ordered and directional chromatographic supports. 1-Pyrenedodecanoic acid was employed for the surface modification of the MWCNTs' stationary phase to adsorb analytes by hydrophobic interactions. This device was used for separating dsDNA fragments of three different lengths (254, 360, and 572,bp), and fluorescence detection was employed to verify the electrokinetic transport in the MWCNT array. The micro-CEC separation of the three compounds was achieved in less than 300,s at a field strength of 66,V/cm due to superior laminar flow patterns and a lower flow resistance resulting from the vertically aligned MWCNTs being used as the stationary phase medium. In addition, a fivefold reduction of band broadening was obtained when the analyte was separated by the chromatographic MWCNT array channel instead of the CE channel. From all of the results, we suggest that an in situ grown and directional MWCNT array can potentially be useful for preparing more diversified forms of stationary phases for vertically efficient chip-based electrochromatography. [source]


Preparative capillary zone electrophoresis using a dynamic coated wide-bore capillary

ELECTROPHORESIS, Issue 15 2006
Mahmoud M. Yassine
Abstract Preparative capillary zone electrophoresis separations of cytochrome,c from bovine and horse heart are performed efficiently in a surfactant-coated capillary. The surfactant, dimethylditetradecylammonium bromide (2C14DAB), effectively eliminated protein adsorption from the capillary surface, such that symmetrical peaks with efficiencies of 0.7,million plates/m were observed in 50-m,id capillaries when low concentrations of protein were injected. At protein concentrations greater than 1,g/L, electromigration dispersion became the dominant source of band broadening and the peak shape distorted to triangular fronting. Matching of the mobility of the buffer co-ion to that of the cytochrome,c resulted in dramatic improvements in the efficiency and peak shape. Using 100,mM bis(2-hydroxyethyl)imino-tris(hydroxymethyl)methane phosphate buffer at pH,7.0 with a 100-m,id capillary, the maximum sample loading capacity in a single run was 160,pmol (2.0,g) of each protein. [source]


A multilayer poly(dimethylsiloxane) electrospray ionization emitter for sample injection and online mass spectrometric detection

ELECTROPHORESIS, Issue 24 2005
Jamie M. Iannacone
Abstract An ESI emitter made of poly(dimethylsiloxane) interfaces on-chip sample preparation with MS detection. The unique multilayer design allows both the analyte and the spray solutions to reside on the device simultaneously in discrete microfluidic environments that are spatially separated by a polycarbonate track-etched, nanocapillary array membrane (NCAM). In direct spray mode, voltage is applied to the microchannel containing a spray solution delivered via a syringe pump. For injection, the spray potential is lowered and a voltage is applied that forward biases the membrane and permits the analyte to enter the spray channel. Once the injection is complete, the bias potential is switched off, and the spray voltage is increased to generate the ESI of the injected analyte plug. Consecutive injections of a 10,,M bovine insulin solution are reproducible and produce sample plugs with limited band broadening and high quality mass spectra. Peptide signals are observed following transport through the NCAM, even when the peptide is dissolved in solutions containing up to 20% seawater. The multilayer emitter shows great potential for performing multidimensional chemical manipulations on-chip, followed by direct ESI with negligible dead volume for online MS analysis. [source]


Raman spectra of apatites: La10,x Si6,y (Al,Fe)y O26,

JOURNAL OF RAMAN SPECTROSCOPY, Issue 1 2007
G. Lucazeau
Abstract Raman spectra of eight polycrystalline apatites of the general formula La10,xSi6,yM,yO26 , with M, = Al or Fe were obtained at 300 K. Raman spectra of La10Si4Fe2O26 and La9.83Si4.5Al1.5O26 were investigated in the range 80,1000 K and 80,623 K, respectively. Tentative assignments of bands to stretching and bending modes of SiO4 tetrahedra and to M'O vibrations are proposed. Except for the two new bands, which appear around 700 cm,1 when Al is replaced by Fe, only some band broadenings and relative intensity changes are observed as a function of the rate of O5 or La vacancies. Most of the bands soften and broaden continuously when raising the temperature. This is an indication that the Al- and Fe-substituted apatites do not undergo any structural change up to 1000 K. Above 1000 K, the broad and weak shoulder observed at 850 cm,1 for La10Si4Fe2O26 is replaced by a strong band at 868 cm,1, suggesting that SiO4 tetrahedra undergo a structural modification. All compounds show the same residual band broadening at 80 K. This suggests that there is a small rate of static disorder preferentially related to the solubility of Al and Fe in the Si sublattice rather than to other defects. Moreover, the observation of FeO modes indicates that the dynamics of the solid solution obeys the so-called two-mode behavior. The occurrence of FeO stretching vibrations 150 cm,1 lower than for those of SiO suggests that the coordination number of iron could be larger than 4, particularly for the Fe4+ species. Copyright 2006 John Wiley & Sons, Ltd. [source]


Online preconcentration using monoliths in electrochromatography capillary format and microchips

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 17 2007
Violaine Augustin
Abstract Online preconcentration and separation of analytes using an in situ photopolymerized hexyl acrylate-based monolith stationary phase was evaluated using electrochromatography in capillary format and microchip. The band broadening occurring during the preconcentration process by frontal electrochromatography and during the desorption process by elution electrochromatography was studied. The hexyl acrylate-based monolith provides high retention for neutral analytes allowing the handling of large sample volumes and its structure allows rapid mass transfer, thus reducing the band broadening. For moderately polar analytes such as mono-chlorophenols that are slightly retained in water, it was shown that enrichment factors up to 3500 can be obtained by a hydrodynamic injection of several bed volumes for 120 min under 0.8 MPa with a decrease in efficiency of 50% and a decrease of 30% for the resolution between 2- and 3-chlorophenol. An 8 min preconcentration time allows enrichment factors above 100 for polyaromatic hydrocarbons. The interest of these monoliths when synthesized in microchip is also demonstrated. A 200-fold enrichment was easily obtained for PAHs with only 1 min as preconcentration time, without decrease in efficiency. [source]


Raman spectra of apatites: La10,x Si6,y (Al,Fe)y O26,

JOURNAL OF RAMAN SPECTROSCOPY, Issue 1 2007
G. Lucazeau
Abstract Raman spectra of eight polycrystalline apatites of the general formula La10,xSi6,yM,yO26 , with M, = Al or Fe were obtained at 300 K. Raman spectra of La10Si4Fe2O26 and La9.83Si4.5Al1.5O26 were investigated in the range 80,1000 K and 80,623 K, respectively. Tentative assignments of bands to stretching and bending modes of SiO4 tetrahedra and to M'O vibrations are proposed. Except for the two new bands, which appear around 700 cm,1 when Al is replaced by Fe, only some band broadenings and relative intensity changes are observed as a function of the rate of O5 or La vacancies. Most of the bands soften and broaden continuously when raising the temperature. This is an indication that the Al- and Fe-substituted apatites do not undergo any structural change up to 1000 K. Above 1000 K, the broad and weak shoulder observed at 850 cm,1 for La10Si4Fe2O26 is replaced by a strong band at 868 cm,1, suggesting that SiO4 tetrahedra undergo a structural modification. All compounds show the same residual band broadening at 80 K. This suggests that there is a small rate of static disorder preferentially related to the solubility of Al and Fe in the Si sublattice rather than to other defects. Moreover, the observation of FeO modes indicates that the dynamics of the solid solution obeys the so-called two-mode behavior. The occurrence of FeO stretching vibrations 150 cm,1 lower than for those of SiO suggests that the coordination number of iron could be larger than 4, particularly for the Fe4+ species. Copyright 2006 John Wiley & Sons, Ltd. [source]