Three dimensional numerical study of the effect of large Grashof number on HEM crystal growth

Heat transfer and fluid flow in HEM crystal growth of silicon in cylindrical cavity is studied numerically. The walls of the crucible are heated to a fixed temperature. The exchanger that causes and induces natural convection is seated at the middle‐bottom of the crucible. The finite‐volume method is employed to solve the governing equations with proper boundary conditions. The effects of transport mechanism on the temperature distribution, melt flow, pressure and stream function are presented. We focus our work on the pressure field which has not yet been studied in HEM crucible. Also, we extend our work on a wide range Grashof number and for large numbers until 10¹² not yet studied in HEM furnace. It is found that the onset of flow fluctuations appears at Gr = 10¹⁰. Uniform temperature is observed in the entire melt at high Grashof number with development of a thermal boundary layer close to the exchanger. The thermal boundary layer thickness is calculated for strong buoyancy regime. Besides, for very high Gr number, buoyancy has less effect on temperature and then on melt‐crystal interface shape. During enlarging Gr, pressure evolution is related to temperature variation more than flow pattern.     

System Design and Emerging Hardware Technology for Ion Chromatography

This review provides an overview of advances in system design for ion chromatography (IC), focusing on the suppressed conductivity detection mode. In particular, advances in automated mobile-phase generation and suppressor technology based on different electrolytic concepts are addressed and novel detection approaches are discussed. Finally, advances in multi-dimensional IC and aspects of miniaturization, including capillary IC instrumentation and chip-based IC, are discussed.     

Influence of blowing on the anisotropy of the Reynolds stress tensor in a turbulent channel flow

The effects of localized wall blowing through a porous strip are investigated using hot-wire anemometry in a turbulent channel flow. Three blowing magnitudes are studied: σ=0.22, 0.36 and 0.58, where σ is the momentum flux gain ratio and that of the incoming channel flow at three different positions from the spanwise porous strip. The main emphasis of this work was the departure from isotropy of the turbulent flow with localized blowing. The anisotropic invariant map (AIM) for the Reynolds stress tensor revealed that blowing decreased the anisotropy of the turbulent structure in the near-wall region, and a decrease in the longitudinal integral length scale was observed when the blowing rate increased.     

A Mild Dihydrobenzooxaphosphole Oxazoline/Iridium Catalytic System for Asymmetric Hydrogenation of Unfunctionalized Dialins

Air‐stable P‐chiral dihydrobenzooxaphosphole oxazoline ligands were designed and synthesized. When they were used in the iridium‐catalyzed asymmetric hydrogenation of unfunctionalized 1‐aryl‐3,4‐dihydronaphthalenes under one atmosphere pressure of H₂, up to 99:1 e.r. was obtained. High enantioselectivities were also observed in the reduction of the exocyclic imine derivatives of 1‐tetralones.     

Capillary electrophoresis using high ionic strength background electrolytes containing zwitterionic and non-ionic surfactants and its application to direct determination of bromide and nitrate in seawater

In capillary electrophoresis, it is commonly considered that even a moderately high ionic concentration in the background electrolyte (BGE) leads to high currents, resulting in Joule heating and serious peak distortion. As a new approach to overcome this problem, zwitterionic (Zwittergent-3-14) and/or non-ionic (Tween 20) surfactants have been added to BGEs containing high salt concentrations (e.g. 0.3 M NaCl) and have been shown to result in acceptable separation currents (<200 microA). In turn, these BGEs could be applied to the separation of samples containing high salt concentrations (such as undiluted seawater) without the occurrence of any significant peak broadening due to electrodispersion of the sample. For example, a BGE comprising 10 mM Zwittergent-3-14, 50 mM Tween 20, 0.3 M NaCl and 5 mM phosphate (ph 7) could be used for the determination of UV-absorbing anions in seawater, giving good peak shapes and detection limits of 0.8 microM and 0.6 microM for nitrate and bromide, respectively. The beneficial effects of the non-ionic surfactant on the separation were attributed largely to suppression of the electro-osmotic flow. On the other hand, the zwitterionic surfactant was found to be capable of the incorporation of some anions in accordance with the behaviour of these same surfactants in electrostatic ion chromatography. This incorporation resulted in a decreased conductivity of the BGE and also a change in the separation selectivity of the system.     

New Triterpene Saponins from Acanthophyllum pachystegium

Four new triterpenoid saponins, pachystegiosides A ( 1 ), B ( 2 ), C ( 3 ), and D ( 4 ), were isolated from the roots of Acanthophyllum pachystegium K. H. Their structures were elucidated by means of a combination of homo‐ and heteronuclear 2D‐NMR techniques (COSY, TOCSY, NOESY, HSQC, and HMBC) and by FAB‐MS. The new compounds were characterized as 3‐O‐{O‐β‐D ‐galactopyranosyl‐(1→2)‐O‐[β‐D ‐xylopyranosyl‐(1→3)]‐β‐D ‐glucuronopyranosyl}quillaic acid 28‐{O‐β‐D ‐xylopyranosyl‐(1→3)‐O‐β‐D ‐xylopyranosyl‐(1→4)‐O‐α‐L ‐rhamnopyranosyl‐(1→2)‐O‐[3,4‐di‐O‐acetyl‐β‐D ‐quinovopyranosyl‐(1→4)]‐β‐D ‐fucopyranosyl}ester ( 1 ), 3‐O‐{O‐β‐D ‐galactopyranosyl‐(1→2)‐O‐[β‐D ‐xylopyranosyl‐(1→3)]‐β‐D ‐glucuronopyranosyl}quillaic acid 28‐{O‐β‐D ‐xylopyranosyl‐(1→3)‐O‐β‐D ‐xylopyranosyl‐(1→4)‐O‐α‐L ‐rhamnopyranosyl‐(1→2)‐O‐[4‐O‐acetyl‐β‐D ‐quinovopyranosyl‐(1→4)]‐β‐D ‐fucopyranosyl} ester ( 2 ), 3‐O‐{O‐β‐D ‐galactopyranosyl‐(1→2)‐O‐[β‐D ‐xylopyranosyl‐(1→3)]‐β‐D ‐glucuronopyranosyl}quillaic acid 28‐{O‐β‐D ‐xylopyranosyl‐(1→4)‐O‐α‐L ‐rhamnopyranosyl‐(1→2)‐O‐[4‐O‐acetyl‐β‐D ‐quinovopyranosyl‐(1→4)]‐β‐D ‐fucopyranosyl} ester ( 3 ), and gypsogenic acid 28‐[O‐β‐D ‐glucopyranosyl‐(1→2)‐O‐β‐D ‐glucopyranosyl‐(1→6)‐O‐β‐D ‐glucopyranosyl‐(1→3)‐β‐D ‐galactopyranosyl] ester ( 4 ).     

Qualitative analysis of some carboxylic acids by ion-exclusion chromatography with atmospheric pressure chemical ionization mass spectrometric detection

A simple, selective and sensitive method for the determination of carboxylic acids has been developed. A mixture of formic, acetic, propionic, valeric, isovaleric, isobutyric, and isocaproic acids has been separated on a polymethacrylate-based weak acidic cation-exchange resin (TSK gel OA pak-A) based on an ion-exclusion chromatographic mechanism with detection using UV-photodiode array, conductivity and atmospheric pressure chemical ionization mass spectrometry (APCI-MS). A mobile phase consisting of 0.85 mM benzoic acid in 10% aqueous methanol (pH 3.89) was used to separate the above carboxylic acids in about 40 min. For LC-MS, the APCI interface was used in the negative ionization mode. Linear plots of peak area versus concentration were obtained over the range 1-30 mM (r2=0.9982) and 1-30 mM (r2=0.9958) for conductimetric and MS detection, respectively. The detection limits of the target carboxylic acids calculated at S/N=3 ranged from 0.078 to 2.3 microM for conductimetric and photometric detection and from 0.66 to 3.82 microM for ion-exclusion chromatography-APCI-MS. The reproducibility of retention times was 0.12-0.16% relative standard deviation for ion-exclusion chromatography and 1.21-2.5% for ion-exclusion chromatography-APCI-MS. The method was applied to the determination of carboxylic acids in red wine, white wine, apple vinegar, and Japanese rice wine.     

Performance of a simple UV LED light source in the capillary electrophoresis of inorganic anions with indirect detection using a chromate background electrolyte

Light emitting diodes (LEDs) are known to be excellent light sources for detectors in liquid chromatography and capillary electromigration separation techniques, but to date only LEDs emitting in the visible range have been used. In this work, a UV LED was investigated as a simple alternative light source to standard mercury or deuterium lamps for use in indirect photometric detection of inorganic anions using capillary electrophoresis with a chromate background electrolyte (BGE). The UV LED used had an emission maximum at 379.5 nm, a wavelength at which chromate absorbs strongly and exhibits a 47% higher molar absorptivity than at 254 nm when using a standard mercury light source. The noise, sensitivity and linearity of the LED detector were evaluated and all exhibited superior performance to the mercury light source (up to 70% decrease in noise, up to 26.2% increase in sensitivity, and over 100% increase in linear range). Using the LED detector with a simple chromate-diethanolamine background electrolyte, limits of detection for the common inorganic anions, Cl-, NO3-, SO4(2-), F- and PO4(3-) ranged from 3 to 14 microg L(-1), using electrostatic injection at -5 kV for 5 s.     

Optimisation of selectivity in the separation of aromatic amino acid enantiomers using sulfated beta-cyclodextrin and dextran sulfate as pseudostationary phases

Control of selectivity in the enantiomeric separation of three aromatic amino acids (phenylalanine, tyrosine and tryptophan) was demonstrated utilising two separate electrolyte additives. Sulfated-beta-cyclodextrin (s-beta-CD) was chosen as the chiral selector while the addition of dextran sulfate provided a means with which to predictably fine-tune separation selectivity. The two additives were found to interact independently with the amino acids, with the s-CD providing chiral interactions while the dextran sulfate provided ion-exchange (IE) interactions. The system was also very robust with reproducibility of migration times being < 2.0% RSD between runs and < 2.6% on using a new capillary. A physical model derived from first principles was also successfully used to describe the two additive system. The model accurately described the observed separations over the range of 0-20 mM s-beta-CD and 0-1% dextran sulfate with a correlation coefficient of 0.998 between predicted and observed mobilities. The physical model also provided useful information about the system including association constants between the analytes and the pseudostationary phases, together with the mobilities of the associated complexes (analyte-cyclodextrin and analyte-dextran sulfate). Selectivity optimisation was achieved using the normalised resolution product and minimum resolution criteria. The physical model also allowed a desired separation selectivity to be obtained, such that experimental conditions could be predicted to lead to a particular migration order.     

Poly(tetrafluoroethylene) separation capillaries for capillary electrophoresis. Properties and applications

Poly(tetrafluoroethylene) (PTFE) is a material widely known for its inertness and excellent electrical properties. It is also transparent in the UV region and has a reasonable thermal conductivity. These properties make PTFE a suitable material for the separation capillary in capillary electrophoresis. Differences in the chemistry of the capillary wall compared to fused silica (FS) can make PTFE an interesting alternative to FS for some special applications. In this work, properties of a commercial PTFE capillary of approx. 100 microm i.d. were investigated, including the dependence of electroosmotic flow (EOF) on pH for unmodified and dynamically modified PTFE, optical properties, and practical aspects of use. The main problems encountered for the particular PTFE capillary used in this study were that it was mechanically too soft for routine usage and the crystallinity of the PTFE caused light scattering, leading to high background absorbance values in the low UV region. The profile of the EOF versus pH for bare PTFE surprisingly showed significantly negative EOF values at pH < 4.2, with an EOF of -30 x 10(-9) m2 V(-1) s(-1) being observed at pH 2.5. This is likely to be caused by either impurities or additives of basic character in the PTFE, so that after their protonation at acidic pH they establish a positive charge on the capillary wall and create a negative EOF. A stable cationic semi-permanent coating of poly(diallyldimethylammonium chloride) (PDDAC) could be established on the PTFE capillary and led to very similar magnitudes of EOF to those observed with FS. A hexadecanesulfonate coating produced a cathodic EOF of extremely high magnitude ranging between +90 and +110 x 10(-9) m2 s(-1) V(-1), which are values high enough to allow counter-EOF separation of high mobility inorganic anions. In addition, pH-independent micellar electrokinetic capillary chromatography (MEKC) separations could be easily realised due to hydrophobic adsorption of sodium dodecylsulfate (used to form the micelles) on the wall of the PTFE capillary. The use of polymers that would be mechanically more robust and optically transparent in the low-UV region should make such CE capillaries an interesting alternative to fused silica.