Laterally attached liquid-crystalline polymers as stationary phases in reversed-phase high-performance liquid chromatography. III. Effect of the local anisotropic order on the separation of polycyclic aromatic hydrocarbons

Specific stationary phases based upon non-liquid-crystalline polymers, liquid-crystalline molecules and side-on fixed liquid-crystalline polymers (SO-LCP) have been synthesized for use as silica modified stationary phases in high-performance liquid chromatography (HPLC). The mesogenic side group of the SO-LCP was composed of three phenyl ring benzoate type with terminal alkoxy chains and was laterally linked to a polysiloxane backbone via an alkyl ester spacer arm. This study demonstrated that the shape recognition of stationary phases based upon SO-LCP towards the length-to-breath ratio (L/B) was strongly connected to the existence of a local liquid-crystalline order into the pores of silica gel, warranting the interest of the collective organization of mesomorphic materials in liquid chromatography. Furthermore, the chromatographic performances depended on the kind of anisotropic order and it was more advantageous to use smectic side-on liquid-crystalline polymer than nematic and obviously non-liquid-crystalline ones. Finally, for a series of polymers having the same mesomorphism, the larger the temperature stability range of the mesophase, the more pronounced the local order effect and the higher the shape recognition.     

Determination of the enantiomeric composition of chiral carboxylic acids using chiral derivatization and HPLC

Summary The enantiomers of chiral carboxylic acids were separated as their diastereomeric amides with (1R,2R)-(−)-1-(4-nitrophenyl)-2-amino-1,3-propanediol (“levobase”) and with “dextrobase” (the enantiomer of levobase) by high-performance liquid chromatography using a conventional C-18 column and various solvent systems containing acetonitrile, methanol, water, and phosphoric acid.     

Lösungsmittel-sensibilisierte strahlungschemische Reaktionen II FRIES-Umlagerungen von Arylestern und Arylamiden [1]

In a series of screening experiments p-tolyl acetate ( 1a ), phenyl benzoate ( 1b ), p-tolyl benzoate ( 1c ), acetanilide ( 1d ), and 2-naphthyl acetate ( 5 ) have been subjected to γ-radiolysis in aromatic and saturated hydrocarbon solutions. Qualitatively, the products formed correspond to those observed also with the respective photo-FRIES reactions, i.e., hydroxy- and amino-aryl ketones due to rearrangements, and products due to homolytic fission into aryloxy and aniline radicals, respectively, were produced. The relatively high G values of conversion in dilute solutions indicate that energy transfer from the solvent is operative. E.g., 0,1 M p-tolyl acetate ( 1a ) in benzene has a G value of over 0.3 for ortho-rearrangement to 2a , and of 0.55 for cresol ( 4a ) formation. Kinetic evidence points to different energy requirements of the ortho-rearrangement and the phenol formation, and to more than one excited state of benzene acting as energy donor. The ratio of the observed rate constants of the energy transfer to self-quenching in benzene is about 80 1 · mole⁻¹ for the ortho-rearrangement to 2a . The over-all reaction is strongly quenched upon addition of p-terphenyl. A comparison of the quantitative data obtained in this work with available published data reveals differences between benzene-sensitized runs with γ radiation and photochemical experiments. Thus, the ratios of ortho vs. para and amphi rearrangement, and of homolytic fission vs. rearrangements are higher in the solvent-sensitized radiolyses.     

Polymeres porteurs de greffons peptidiques: Polymérisation et copolymérisation de monomères styréniques parasubstitués par des oligopeptides

Polymers and copolymers with peptide pendant chains have been prepared by polymerization and copolymerization of styrene with para styryl peptide monomers terminated by a carboxylic acid or primary amine group.

Polymerizations of I and II have been initiated by AIBN, in tetrahydrofuran or N,N-dimethylformamide. For polymers with functional ends on side-chains protected by urethane functions (amino group) or ester function (acid group), polymer regeneration has been carried out by acidolysis (urethane) and basic hydrolysis (ester). The influences of monomer structure on polymerization yield and the water solubility after neutralisation, have been considered. Copolymerizations of styrene with I and II have been studied. Random copolymers, with solubility in various solvents depending on their composition, have been obtained. Reactivity ratios have been determined.     

The spectrophotometric determination of zirconium with disodium 3-hydroxy-4-[(6-methyl-2-pyridyl)azo]-2,7-naphthalenedisulfonate N-oxide

Summary The application of the reagent for the spectrophotometric determination of traces of zirconium is described. The effects due to acid concentration, reagent concentration, time and diverse ions are reported. Beer's law is obeyed and the molar absorbance coefficient at 577 nm is 3.2×10⁴.

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Die spektrophotometrische Bestimmung von Zirkonium mit Natrium-3-hydroxy-4-[(6-methyl-2-pyridyl) azo]-2,7-naphthalindisulfonat-N-oxid

Zusammenfassung Die Anwendung des genannten Reagens auf die spektrophotometrische Bestimmung von Zirkoniumspuren wurde beschrieben. Der Einfluß der Säurekonzentration, der Reagenskonzentration, der Zeit und verschiedener Fremdionen wurde untersucht. Das Beersche Gesetz wird befolgt; der molare Extinktionskoeffizient bei 577 nm beträgt 3,2 · 10⁴.

     

Selenium speciation by coupling vesicle mediated HPLC with off-line ETAAS and on-line focused microwave digestion HG-AAS detection

A novel High Performance Liquid Chromatography (HPLC) method for the separation of selenium species with specific detection by off-line Electrothermal Atomization Atomic Absorption Spectrometry (ETAAS) or on-line focused microwave digestion (MW) Hydride Generation Atomic Absorption Spectrometry (HG-AAS) is described. Vesicular mobile phases of the cationic surfactant didodecyldimethylammonium bromide (DDAB) have been evaluated for the liquid chromatographic separation of inorganic selenium (selenite and selenate) and different selenoaminoacids (selenocystine, selenomethionine and selenoethionine) on a C(18) reversed-phase column modified by DDAB molecules. The effects of different parameters (pH, buffer and vesicle concentrations) of the mobile phase on the retention times have been determined. The detection limit for selenium with the proposed off-line HPLC-ETAAS method has been found to be 5 microg/L of Se. The detection limit using HPLC-"on line" focused microwave digestion-HG-AAS has been found to be 1 microg/L of Se, with a precision (repeatability) better than +/- 5%. The latter proved to be an exceptional on-line real-time chromatographic detector for selenium speciation purposes.     

Liquid Chromatography-Electrospray Mass Spectrometry Determination of Ibogaine and 12-Hydroxy-Ibogamine in Human Urine

A specific and sensitive liquid chromatography-electrospray ionization mass spectrometry method was developed for the determination of ibogaine and noribogaine in human urine. The work-up procedure involved a solid phase extraction of the compounds and the internal standard (fluorescein) using Oasis HLB columns. The system used a Zorbax eclipse XDB C8 analytical column packed with 5µm diameter particles as the stationary phase. The mobile phase consisted of a 20-min gradient (mobile phase A: 0.02% (v/v) trimethylamine in acetonitrile, mobile phase B: 2 mM ammonium formate buffer (pH 3)). Mass spectrometric data were acquired in single ion monitoring mode at m/z 311.1, 297.2 and 333 for ibogaine, noribogaine and fluorescein, respectively. The drug/internal standard peak area ratios were linked via a quadratic relationship to concentrations (1.78?358 μg L^?1 for ibogaine; 2?400 μg L^?1 for noribogaine). Precision ranged from 5.8 to 14.8% and accuracy was between 93.2 and 112.9%. Mean extraction recoveries of ibogaine, noribogaine and fluorescein were 70.0, 81.7 and 94.8%, respectively. The extraction efficiency was independent of concentration over the range studied. The lower limits of quantitation were 1.78 μg L^?1 for ibogaine and 2 μg L^?1 for noribogaine. In this paper, extensive stability testing was undertaken using a wide range of storage conditions. This method was found suitable for urine analysis of a poisoning involving ingestion of drink made from powdered root of shrub Tabernanthe iboga.     

Effect of gas pressure and pulse length on the isotopically selective multiphoton dissociation of CF3Cl under CO2 laser pulses

The multiphoton dissociation of CF₃Cl induced by TEA-CO₂ laser pulses has been studied in a focused beam geometry. TheR(10) [00°1–02°0] ( ) laser line was used, so as to dissociate preferentially the minor isotopic component¹³CF₃Cl. The isotopic selectivityS and the dissociation probability per pulse ω were measured in the pressure range between 0.25 and 8 Torr. With short laser pulses (90 ns FWHM),S is found to increase slightly with gas pressure up to 2 Torr, and ω, to increase almost linearly over the whole pressure range studied. A schematic model is proposed which satisfactorily explains these results if the transition rates across the energy level spectrum of the CF₃Cl molecules are assumed to increase with gas pressure.     

Intrinsic and extrinsic factors in anion electron-stimulated desorption: D- from deuterated hydrocarbons condensed on Kr and water ice films

The results of D(-) ion desorption induced by 3-20 eV electrons incident on condensed CD(4), C(2)D(6), C(3)D(8), C(2)D(4), and C(2)D(2) are presented. These compounds were deposited in submonolayer amounts on the surfaces of multilayer solid films of Kr and nonporous and porous amorphous ice. While desorption of the D(-) anions proceeds via well-known processes, i.e., dissociative electron attachment (DEA) and dipolar dissociation, significant perturbations of these processes due to presence of the different film substrates are observed. We have shown that it is possible to distinguish between the character and nature of these perturbations. The presence of the nonporous ice perturbs the D(-) desorption intensity by affecting the intrinsic properties of the intermediate anion states through which dissociation proceeds. On the other hand, the presence of the porous ice introduces extrinsic effects, which can affect electron energy losses prior to their interaction with the hydrocarbon molecule and/or the energies and intensities of the fragment species after dissociation. Simple mechanisms responsible for the observed variations in the intensities of desorbed anionic signals are proposed and discussed. Electron transfer from transient anion states to electron states of the substrate film or nearby hydrocarbon molecules appear as the most efficient mechanism to reduce the magnitude of the DEA process.