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The influence of N -benzylideneanline conformation on retention is studied in normal phase liquid chromatography. The effects responsible for retention are investigated using different organic modifiers in the eluent which give specific basic or acidic interactions. Retention is measured with three eluents and the molecular conformations are calculated using semi-empirical methods. The topological and correspondence factor analyses of retention and conformation of compounds show that retention is principally governed by polar interactions and secondary electronic effects. These electronic effects are due to the influence of substituents, either on the benzylidene or aniline rings, on molecular conformation and on the nitrogen charge. The electronic effects are revealed by the influence of the basic or acidic interactions of the eluent.

The Cornell University Portable Radar Interferometer (CUPRI) made high resolution vertical radar measurements of the equatorial electrojet above Alcântara, Brazil from mid-August to mid-October, 1994, as part of the Guara Dip Equator Campaign. Spectra obtained during the period of a few hours before sunrise show the usual nighttime persistence asymmetry wherein there is a preponderance of downward type-I phase velocities as a function of time. These are the first high resolution measurements in South America of this effect at a location other than Jicamarca, Peru. Furthermore the CUPRI interferometer phase data clearly indicate that when changes in the sign of the dominate type-I peaks occur, they are tied to the normal phase progressions of the large scale waves. No reversal of the asymmetry (as does occur in the daytime) was seen in this nighttime period.

We present NMR experiments in the normal phase (T > Tc) in underdoped HgBa2Ca2Cu3O8+δ single crystals (Tc = 115 K) and YBa2Cu3O6.5 (Tc = 46 K in zero field). Through these examples, and on a more general basis, we discuss the signature of the pseudo-gap as observed in NMR experiments and how it compares with other techniques, like transport, specific heat, inelastic neutron scattering and photoemission.

Hydrocarbons from a new strain of the green microalga Botryococcus braunii, the Yayoi strain, were characterized. Normal phase high pressure liquid chromatography on a silver nitrate-coated silica gel column was effective to isolate the hydrocarbons. Chemical structures of a C34 and two novel C33 botryococcene isomers, in addition to known hydrocarbons, were elucidated by gas chromatography-mass spectrometry and nuclear magnetic resonance spectrometry. © 1997 John Wiley & Sons, Ltd.

The composition of 31 genuine Uruguayan lemon oils obtained by industrial processing (FMC on line) during the 1995 season is reported. The samples were representative of all production areas situated in the North and South of Uruguay. The volatile fraction was analysed by HRGC‐FID and GC‐MS; the enantiomeric distribution of b-pinene, sabinene, limonene, linalol, terpinen-4-ol and a-terpineol was studied by multidimensional HRGC‐ HRGC; coumarins and psoralens present in the non-volatile residue were analysed by normal phase HPLC. The results relative to the volatile fraction were compared with those obtained for Uruguayan oils produced in the 1992 and 1993 seasons and for Italian FMC oils. Coumarins and psoralens have been analysed for the first time in Uruguayan oils; their content is compared with that of Italian oils. #1997 by John Wiley & Sons, Ltd.

The dynamics of the S - N transition of a thin HTSC film heated by microwave radiation is studied theoretically. The dependence of the NS-interface propagation velocity v on the microwave power P is found by solving the non-stationary heat balance equation. Two-dimensional effects related to a non-linear heating over the thickness of a substrate, of which the reverse side is stabilized at a temperature , are shown to be essential for calculations of the dependence v(P). A qualitative model which allows one to explain specific features of the NS-interface propagation is proposed. Analytical results are confirmed by a direct numerical simulation of the S - N transition process and differ appreciably from the prediction of the conventional one-dimensional theory. The results obtained may be of importance in the study of the S - N transition in superconducting microwave devices.

Only a small fraction of all separations by high-performance liquid chromatography are performed at normal-phase conditions and especially on silica. Plain silica has the reputation that it is inconvenient to use due to long equilibration times. At least for solvents of low and moderate polarity this is not true, as is shown here with the reproducible separation of ten compounds with gradient elution; solvents are hexane and dichloromethane or hexane and tert.-butyl methyl ether. Short re-equilibration times could especially be obtained with hexane-dichloromethane gradients.

We have studied theoretically the property of the charge-density waves at a surface or interface and their STM images. The self-consistent numerical approach presented here is based on the formalism of the recursion-transfer matrix with the tight-binding Hamiltonian. We show that charge-density waves can be modified under the presence of the surface due to the contact with the normal phase, or the bias voltage of the STM tip. The tunnel current of STM is calculated by a Laudauer-type formula.

We predict on the basis of the Ginzburg-Landau theory that a type-I superconductor can exhibit an interface delocalization or “wetting” transition, in which a macroscopically thick superconducting layer intrudes from the surface into the bulk normal phase. The condition for this transition to occur is that the superconducting order parameter |Ψ|2 is enhanced at the surface. Surprisingly, the order of the wetting transition is controlled by a bulk material constant, the Ginzburg-Landau parameter κ. First-order wetting is predicted for 0 ≤ κ < 0.374, and critical wetting for 0.374 < κ < 1/√2. The possibility of critical wetting is especially interesting because this phenomenon has largely eluded experimental verification in any system until now.

Supercritical fluid chromatography was applied to evaluate the direct chiral discriminative properties of Chiralcel OJ, a tris(4-methylbenzoate) cellulose column towards frequently administered drugs. Two groups of acidic drugs, profen and barbiturate derivatives, and a few basic drugs of the benzodiazepine type were analysed. The effect on enantioselectivity of carbon dioxide when using methanol are acetonitrile as primary modifier was studied. Acetonitrile proved to be a good alternative for methanol, especially for the profen compounds that were not well resolved using methanol. The results were compared to normal phase chromatographic applications on the same column. SFC was not necessarily superior to high-performance liquid chromatography. Chirality 9:126–132, 1997. © 1997 Wiley-Liss, Inc.

Hot pressing characteristics of clays have been done for the following aspects. (i) In achieving high density of the products; (ii) To reveal the mechanism of densification; (iii) To study the mineralogical changes in comparison to normal phase change taking place during usual heating. RHP was first noted by Hedvall (1938) and is commonly called “Hedvall effect.” Pressure is applied during a phase change where there is enhanced reactivity and consequently it assists densification.

Three stereoselective HPLC methods have been developed for the chiral separation of the enantiomers of three intermediates in the preparation of (+)-tanikolide. The enantiomers were separated on Chiralpak IC (250 × 4.6 mm, 5 μm) in normal phase HPLC. Three intermediates were all baseline separated (RS = 2.84, 2.58 and 3.58, respectively). By comparing the chromatograms of racemates and single enantiomers of the three intermediates, the e.e. values of the single enantiomers were determined and calculated.

We study the gravity duals of striped holographic superconductors in the AdS black hole and AdS soliton backgrounds. We show the dependences of the condensation and the critical temperature/critical chemical potential on the inhomogeneity in these two different spacetimes. By exploring the dynamics of the normal phase through the scalar field perturbation, we argue that the pair susceptibility and the conductivity can be possible phenomenological indications to disclose the property of inhomogeneity., 16 pages

Rapidly rotating nuclei provide us good testing grounds to study the pairing correlations; in fact, the transition from the superfluid to the normal phase is realized at high-spin states. The role played by the pairing correlations is quite different in these two phases: The static (BCS like mean-field) contribution is dominant in the superfluid phase, while the dynamic fluctuations beyond the mean-field approximation are important in the normal phase. The influence of the pairing fluctuations on the high-spin rotational spectra and moments of inertia is discussed.

This paper presents a general overview of the application of hydrophilic interaction chromatography (HILIC) in the analysis of antibiotics in different sample matrices including pharmaceutical, plasma, serum, fermentation broths, environmental water, animal origin, plant origin, etc. Specific applications of HILIC for analysis of aminoglycosides, β-lactams, tetracyclines and other antibiotics are reviewed. HILIC can be used as a valuable alternative LC mode for separating small polar compounds. Polar samples usually show good solubility in the mobile phase containing some water used in HILIC, which overcomes the drawbacks of the poor solubility often encountered in normal phase LC. HILIC is suitable for analyzing compounds in complex systems that elute near the void in reversed-phase chromatography. Ion-pair reagents are not required in HILIC which makes it convenient to couple with MS hence its increased popularity in recent years. In this review, the retention mechanism in HILIC is briefly discussed and a list of important applications is provided including main experimental conditions and a brief summary of the results. The references provide a comprehensive overview and insight into the application of HILIC in antibiotics analysis.

Heteroclitin D (H.D) was successfully isolated from Kadsurae Caulis by using flash chromatography and recrystallized by methanol, 10.2 mg of H.D was obtained from 4.86 g of crude extract, and the purity determined by HPLC was 99.4%. The structure was identified by UV, IR, MS, and NMR analysis. The fast, simple and efficient method can be applied to the preparation of reference substance of H. D. Keywords: Kadsurae Caulis, Heteroclitin D, Normal-phase flash chromatography

The technology of analyzing the pharmacological and toxicological properties of chiral drugs has become more commonly utilized since the knowledge of the biological actions of enantiomers has been gradually acquired during the last few decades. This work reviews the applications of chiral liquid chromatography coupled to tandem mass spectrometry (LC –MS) for the analysis of chiral pharmaceuticals since 2005. The enantioselective determinations in pharmaceutical and biomedical fields with LC–MS are classified based on three mobile phase modes, including normal phase, reversed phase and polar organic solvent, in terms of their compatibility with various ionization sources and specific applications.

Multiplicity fluctuation of the target evaporated fragments emitted in 290 A MeV 12C-AgBr, 400 A MeV 12C-AgBr, 400 A MeV 20Ne-AgBr and 500 A MeV 56Fe-AgBr interactions is investigated using scaled factorial moment method in two-dimensional normal phase space and cumulative variable space, respectively. It is found that in normal phase space the scaled factorial moment (ln) increases linearly with increase of the divided number of phase space (lnM) for lower q-value and increases linearly with the increase of lnM and then becomes saturated or decreased for higher q-value, in cumulative variable space ln decreases linearly with increase of lnM, which indicates that no evidence of non-statistical multiplicity fluctuation is observed in our data sets. So any fluctuation indicated in the results of normal variable space analysis is totally caused by non-uniformity of single-particle density distribution., Comment: 10 Pages, 4 figures

We report the first direct observation of an incommensurate lattice distortion in dielectric crystals by an atomic-force microscope. The layered crystal (NH3C3H7)2MnCl4 has been imaged in the normal and incommensurate phases. In the normal phase, we observe well-ordered atomic corrugations on a cleavage surface of a crystal. In the incommensurate phase, these atomic corrugations are modulated by a long periodic plane-wave distortion.

Polycyclic aromatic hydrocarbons (PAHs) and some of their nitrated derivatives (nitro-PAHs) have been measured in atmospheric particulate matter sampled from Birmingham, UK and Damascus, Syria. Sample clean-up and enrichment was carried out by solid phase extraction and normal phase HPLC-fractionation. The first fraction was analysed for PAH by reverse phase HPLC with UV-visible and programmed fluorescence detection. The second fraction was analysed for nitro-PAH by reverse phase HPLC with selective fluorescence detection after post-column reduction to their highly fluorescent amino-PAH.

Photostabilizer-type HALS were analyzed by reverse-and normal-phase liquid chromatography (HPLC) using C-18, cyano, silica, and amino columns with different solvent mixtures as the mobile phase. The stabilizers analyzed were Tinuvin 770 and Chimassorb 944. The best separation was attained using a NH2-column and acetonitrile/water as the mobile phase. Also, three types of extraction procedures were performed to isolate these additives from the polymeric matrix. The most efficient extraction method was achieved by refluxing the sample with toluene. Recoveries of 95% were found for additives using this method.

The x-ray-diffraction experiment of [N(${\mathrm{CH}}_{3}$${)}_{4}$${]}_{2}$${\mathrm{CuCl}}_{4}$ under hydrostatic pressure has revealed the existence of a special confluent point, denoted by L* in the pressure-temperature (p-T) phase diagram, among the prototypical normal phase, the incommensurate phase, and the commensurate phase characterized by the wave vector q=c*/3. With increasing pressure, the incommensurate phase with qc*/3 decreases its own stable temperature range and vanishes at L*. The incommensurate region with q\ensuremath{\gtrsim}c*/3 appears at L* and widens with increasing pressure. On the p-T phase diagram the second-order normal-incommensurate and the first-order incommensurate-commensurate phase lines meet at L*. The wave vector in both incommensurate regions goes continuously to c*/3 and the jump of the satellite intensity on the first-order incommensurate-to-commensurate phase transition becomes small, as the L* point is approached. These experimental facts show that the L* point is a multicritical point in incommensurate systems. These features of the obtained phase diagram are different from those of the universal one for [N(${\mathrm{CH}}_{3}$${)}_{4}$${]}_{2}$M${\mathrm{Cl}}_{4}$ (M=Mn, Fe, and Zn) reported previously. \textcopyright{} 1996 The American Physical Society.

The separation and identification of flavones present in a chloroform extract of Baccharis trinervis leaves was investigated. The chromatographic system consisted of a amino-bonded column, gradient elution from hexane-chloroform (85:15) to chloroform-acetonitrile (40:60) and detection at 346 nm. Four flavones were found. From NMR and MS data they were identified as 5-hydroxy-7,4′-dimethoxyflavone (I), 5-hydroxy-7,3′,4′-trimethoxyflavone (II), 5,3′-dihydroxy-7,4′-dimethoxyflavone (III) and 5,4′-dihydroxy-7-methoxyflavone (IV). Flavone II and III have not been found in Baccharis trinervis before. The chromatographic system showed good selectivity for the separation of the flavones. The relation between tR and the structure is discussed.

This paper investigates the behaviour of silica, alumina, titania, zirconia and the novel mesoporous aluminosilicate MCM-41 in normal-phase high-performance liquid chromatography under comparable conditions. The physicochemical properties of the oxides and MCM-41 are described. MCM-41 is an ordered mesoporous material with a regular pore structure composed of an assembly of hexagonal tubes with a pore diameter of 4 nm. In chromatography MCM-41 exhibits acid and basic properties and proves to be suitable for the separation of acid, neutral and basic compounds.

Incommensurate deviation δ and quality factor Q of ZrTiO4 with the various cooling rates were measured. With decrease of cooling rate, the successive phase transitions were observed: high temperature disordered normal phase (N) — incommensurately modulated ordered phase (IC) -commensurately ordered phase (C). It was ascribed to the IC — C transition that δ decreases and Q increases below the cooling rate of 1° C/h.

The retention behaviour of sulphated oligoethylene glycol nonylphenyl ether anionic surfactants was investigated in normal-phase systems with nitrile and amino chemically bonded stationary phases and with organic mobile phases containing tetraalkylammonium additives. Non-linear plots of the logarithms of capacity factors versus the number of oxyethylene units in sulphated oligomers were observed on the bonded amino column in mobile phases consisting of cetyltrimethylammonium bromide, 2-propanol and n-heptane. It is possible to separate sulphated oligomers and their parent non-sulphated analogues in a single run in these systems using gradient elution.

Retention behaviour of un-sulphated and sulphated, oligoethyleneglycol nonylphenyl ether, anionic surfactants was investigated in normal-phase LC systems with chemically bonded amino stationary phase in organic mobile phases containing water and cetyl trimethylammonium bromide (CTAB). Addition of water to the mobile phase improves efficiency of separation and linearity of the dependences of logk′ versus number of oxyethylene units in the sulphated oligomers, so that it is possible to describe simultaneous effects of this number and of the concentration of CTAB on retention by a simple equation. In this system, it is possible to separate lower sulphated and un-sulphated oligomers in a single run in 10–15 min under isocratic conditions.

A previously published [1] liquid chromatographic method for the determination of ochratoxin A in corn, barley and kidney has been modified for application to parboiled rice with quantification by high performance thin layer chromatography (HPTLC). The method has been validated by spiking uncontaminated extracts of rice with ochratoxin A over the range 0 to 198 μg kg−1. The proposed method has some significant advantages over the current AOAC method [2], especially for determining low levels of ochratoxin A in parboiled rice.

Raman-scattering experiments have been performed to study the successive phase transitions of ${\mathrm{Rb}}_{2}$${\mathrm{ZnCl}}_{4}$ over the temperature range 15\char21{}400 K in the Zn-Cl stretching mode region. The observation of extra Raman lines, not predicted by group theory in the normal phase, reveals that ${\mathrm{Rb}}_{2}$${\mathrm{ZnCl}}_{4}$ possesses an orientational disorder of the chlorozincate groups. At low temperature, Raman-scattering spectra clearly exhibit two phase transitions at 80 and 50 K. These ones are strongly correlated with the disorder observed in the normal phase.

A new route using an aldolization reaction has been investigated in order to synthesize a precursor of pilocarpin, an alkaloid having sympathomimetic properties. To study the stereoselectivity of this route and to propose a mechanism, liquid chromatography has been used to analyse and to isolate each diastereoisomer for a structural determination by NMR. To further investigate the reaction mechanism, seven different aldehydes (or ketones) were used in the aldolization reaction, producing seven different mixtures. This paper describes the improvement of LC conditions with diol- and amino-bonded silica and the nonaqueous mobile phases required for the isolation of each isomer. Keywords: diastereoisomers, pilocarpin precursor, normal phase liquid chromatography, diol- and amino-bonded silicas.

The partition function of the double-layer $XY$ model in the (dual) Villain form is computed exactly in the limit of weak coupling between layers. Both layers are found to be locked together through the Berezinskii-Kosterlitz-Thouless transition, while they become decoupled well inside the normal phase. These results are recovered in the general case of a finite number of such layers. When re-interpreted in terms of the dual problems of lattice anyon superconductivity and of spin-liquids, they also indicate that the essential nature of the transition into the normal state found in two dimensions persists in the case of a finite number of weakly coupled layers., Comment: 10 pgs, TeX, LA-UR-94-3941

A semi-empirical model for the atomic-scale structure of liquid Si and Ge has been constructed on the basis of atomic arrangements with the structure of the normal and high-pressure phases of solid Si and Ge. It has been found that liquid Si and Ge have quite similar atomic orderings, exhibiting the local tetrahedral features of the considered solid phases of Si and Ge where the features of the high-pressure phase predominate over those of the normal phase. The present model picture has been found to account well for the peculiar character of the solid-liquid phase transition in Si and Ge.

It is shown that when the density becomes larger than a critical density an ensemble of water molecules evolves towards a coherent ground state, where molecules oscillate in phase with the e.m. field. At each temperature, liquid water is found to consist of a coherent phase of molecules in such a ground state and of a normal phase, whose population is determined by thermal excitations. The observed thermodynamical quantities as well as their wellknown anomalous behaviors are satisfactorily described by our theory.

The application of an enhanced-fluidity liquid mixture (n-hexane-CO2) as a mobile phase in normal-phase HPLC using a 3-cyanopropyl polysiloxane stationary phase was evaluated. Decreased pressure drop across the chromatographic column was observed with increasing proportions of added CO2 to the mixtures. For selected mixture conditions, increased efficiency and decreased peak asymmetry were obtained in comparison to that for separations with 100% n-hexane. A limiting amount of CO2 that could be added to hexane was found. If more CO2 was added past that limit, serious peak asymmetry lowered the measured column efficiency.

A normal-phase High Performance Liquid Chromatography (HPLC) method was developed for the determination of dehydroepiandrosterone (DHEA) in food supplements. We have used an HPLC 200 (Perkin Elmer, USA) with a spectrophotometric detector LC-785A (Bioanalytical systems, USA) and a thermostat (Perkin Elmer, Waltham, MA, USA). We have chosen isocratic HPLC elution, column: LiChrospher (100 DIOL 250 x 4 mm х 5 μm), mobile phase: acetonitrile: water = 98: 2 v/v, flow rate: 1 ml/min. and detection at λ = 202 nm. We have found that this method allows fast and selective qualitative and quantitative determination of DHEA in pharmaceutical products.

Using supercritical fluid chromatography (SFC), the direct separation of a series of β-blockers has been carried out on the commercially available ChyRoSine-A and on its improved version. Surprisingly, these solutes appeared to be poorly resolved using normal phase liquid chromatography (NPLC). The chromatographic behaviors (both in SFC and NPLC) of various analogues of propranolol have been stidied, and after spectroscopic investigations have been carried out. Starting from these data, a detailed chiral recognition mechanism has been elaborated based on molecular modeling. It appeared that the solvating effect of carbon dioxide induces a change of the propranolol conformations that is geometrically favorable to the chiral discrimination, this change of conformation occurs in the presence of carbon dioxide of if the solute bears both an vino proton and an ether function separated the one from the other by three carbon atoms

We have investigated the collision of3He drops in the normal phase by means of the Vlasov equation. The structure and dynamics of the drops have been described by a density functional that takes properly into account relevant properties of the homogeneous liquid. Results for3He250-3He250 collisions at different energies and impact parameters are presented.

Several mechanisms can extend the equilibrium domain of a liquid phase into the solid region of the normal phase diagram. The causes of premelting, which include surface melting, interface curvature and substrate disorder, occur in all types of substances, including H2O. In the case of H2O, premelting can have important environmental consequences, among which are the heaving of frozen ground, breakdown of rock and concrete, sintering of snow, flow of glaciers, scavenging of atmospheric trace gases by snow and ice, and the electrification of thunderclouds. The article reviews the basic mechanisms of premelting and discusses their roles in the environmental phenomena. The principal results of numerous studies are reviewed, and trends in current research are outlined.

A procedure consisting of connecting in series two different HPLC columns, one for size-exclusion chromatography (SEC) and the second one a normal-phase (silica) column has been developed. An automatic three-way switching valve was placed between the two columns. Through the valve, the polymer was drained whereas the rest of the compounds, a group of antioxidants and UV stabilizers, were separated and analyzed in the second column. The behaviour of the SEC column in different organic phases is studied. Detection limits about 0.1 μg ml −1 were obtained for BHT, Tinuvin 326 and Tinuvin 327; 0.2 μg ml −1 for Irganox 1076, and 1.1 μg ml −1 for Cyasorb UV 9 and Cyasorb UV 1084. R.S.D. values of the whole process are lower than 4%.

A method is described for a normal-phase separation and quantification of polynuclear aromatic hydrocarbons (PAHs) using high performance liquid chromatography (HPLC) coupled with UV-diode array detection. The method employed takes advantage of the inherent capabilities of a «charge-transfer» normal-phase HPLC column (Holstein, W. Chromatographia 1981, 14, 468), the Hypersil PAH-2 column (Keystone Scientific, Inc., Bellefonte, PA), and the ability of the diode array detector to provide UV spectra for each eluting compound having chromophores in the UV range which allows for separation, identification, and quantification in the normal phase of individual PAHs. Elaborate sample preparations, which in the past have accompanied determination and separation of individual PAHs, can be avoided for the analysis of PAHs in either extracts of natural samples or complex fuel mixtures. The potential for this method was demonstrated by the separation and quantification of five well-studied coal liquefaction process stream samples. PAHs having from two rings up to nine rings, along with their isomers and alkylated derivatives, were separated and quantified using this method. Clear differences were observed among liquefaction process streams due, in large part, to differences in feed coals and process conditions

Objective: The objective is defined to develop and validate simple, rapid, precise, and accurate for separation and determination of R-isomer impurity of ketoprofen bulk drug material by the normal phase high-performance liquid chromatographic method as per the International Conference of Harmonization Guideline (ICH) guidelines. Methods: The R-isomer and S-isomer were baseline resolved on a Chiralcel OJ-H, 150 mm × 4.6 mm, and 5 µm stationary phase column. Mobile phase system containing n-hexane:isopropyl alcohol:glacial acetic acid (50:50:0.1 v/v.). The detector wavelength has been selected 254 nm and column oven temperature 25°C. The chromatographic resolutions between R-isomer and S-isomer were more than two. The developed method was extensively validated according to ICH guidelines. R esults: Ketoprofen linearity was found for R-isomer over the concentration range of 600-6000 ng/ml, with the linear regression (Correlation coefficient R=0.999) and proved to be robust. The limit of detection and limit of quantification of ketoprofen R-isomer were found to be 200 and600 ng/ml. The percentage recovery of R-isomer has been ranged from 97.5 to 102.0 in bulk drug material samples of ketoprofen. The proposed method was found to be suitable and accurate for the quantitative determination of R-isomer of ketoprofen in bulk drug sample. C onclusion: A simple, rapid, precise, and accurate normal phase liquid chromatography method has been developed and validated to determineR-isomer impurity of ketoprofen in bulk drugs material as per ICH. Keywords: Ketoprofen, High-performance liquid chromatography, Known impurity, Normal phase, Chiralcel OJ-H, Validation.