Rapid determination of aliphatic amines in water samples by pressure-assisted monolithic octadecylsilica capillary electrochromatography-mass spectrometry

A pressure-assisted capillary chromatography-mass spectrometry method based on the use of a monolithic octadecylsilica (ODS) capillary is proposed for the determination of aliphatic amines. A 25 mM citric acid buffer containing 10% methanol is used as running electrolyte. Separation is achieved by simultaneously applying a capillary electrophoresis (CE) voltage of 13 kV and an overimposed pressure of 8 bar. The use of pressure is required to ensure stable electrospray conditions. Analysis times are reduced by using a capillary column consisting of a 30 cm long monolithic silica capillary column bound with ODS and a fused-silica capillary column also 30 cm long. The proposed method was successfully applied to the determination of low-molecular-weight aliphatic amines in tap and river water. The analysis of real samples requires cleanup and preconcentration, which can be performed automatically by inserting a minicolumn in the replenishment system of the commercial instrument.     

De novo synthesis of 4'-ethoxy nucleoside analogues

Butenolides 5a and 13 were used as optically active templates in the de novo synthesis of 4'-disubstituted nucleoside analogues. The butenolides were reduced and acylated in situ to give acetates 10 and 14. Vorbrüggen coupling gave the protected nucleoside analogues 11 and 15. Reduction of 11 gave 4'-ethoxy-2',3'-dideoxythymidine (6) and deprotection of 15 gave 4'-ethoxy-2',3'-dideoxydidehydrothymidine (7). The cis-dihydroxylation of a variety of butenolides occurred with the major product formed from oxidation of the beta-face.     

Determination of ambroxol in an automated multi-pumping pulsed flow system.

A new flow methodology exploiting the multi-pumping approach was developed for the spectrophotometric determination of ambroxol hydrochloride in pharmaceutical preparations. The flow manifold was implemented by using, exclusively, multiple solenoid-actuated micro-pumps, which acted simultaneously as sample insertion, solutions propelling and reagents commutation units. Linear calibration plots were obtained over an ambroxol concentration ranging from 10 to 200 mg l(-1) (r.s.d. < 0.5%, n = 15) and a sampling rate of about 60 samples per hour (flow rate = 1.92 ml min(-1), sample volume = 80 microl).     

Adsorption of anionic dyes on chitosan beads. 1. The influence of the chemical structures of dyes and temperature on the adsorption kinetics

In this work, chitosan beads were synthesized in acidic medium and cross-linked in 1% glutaraldehyde solution. The characterization of the materials using TG/DTG, XRD, and BET surface areas showed that the beads did not modify their characteristics after the cross-linking reaction. The cross-linked beads were utilized as adsorbents for the removal of the yellow-, blue-, and red-anionic reactive dyes from aqueous solutions at pH 2.0. Adsorption of the yellow-dye increased from 25 to 50 degrees C. However, adsorption of the blue-dye decreased from 25 to 50 degrees C. Interestingly, the adsorption of the red-dye decreased from 25 to 35 degrees C and increased from 45 to 50 degrees C. The kinetic data were evaluated using an Avrami kinetic model, where the parameter n was related to the determination of changes in the adsorption mechanisms. Adsorption data of the dyes in relation to the contact time, the chemical structures of the dyes, and temperature were presented and were discussed.     

Sulphate preconcentration by anion exchange resin in flow injection and its turbidimetric determination in water

A preconcentration procedure was established for sulphate determination in rain waters at the mg/l level, employing a small column packed with the AG1-X8 (200-400 mesh) anionic resin inserted into a flow injection system. Sulphate determination was performed by using the turbidimetric method based on reaction with barium. For concentrations within 0.10 and 2.0 MgSO(2-)(4)/l, a throughput of 50 determinations/hr was achieved, and the relative standard deviation of results was better than 2%.     

A theoretical investigation of the interaction between H,Li, Na,K, and fullerenes

We studied the interaction between H, Li, Na, and K with one and two C₆₀ molecules using unrestricted Hartree–Fock (UHF) methods. We investigated the effects of distances between the doping atoms and the C₆₀ clusters, total charges, interaction energies, stabilities, HOMO‐LUMO energy differences, charge distribution, and potential energy surfaces. The effect of each doping atom was analyzed and potential technological applications discussed. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Comparison of the Structural Information on Sol-Gel Systems Provided by Pyrene Labeled Fluorescent Probes

The influence of the acid catalyst concentration on the structural evolution of a sol-gel system was studied by doping TEOS based starting solutions with two fluorescent probes: a polystyrene chain (M _n =1700) and a much shorter alkane chain (M=172), both of them labeled at both ends with 1-pyrenyl. For this purpose, each probe was incorporated in two TEOS∶H₂O∶C₂H₅OH mixtures (molar ratios 1∶4∶1), one at pH 1.2 and the other at pH 2.5 (respectively below and above the isoelectric point of silica). Very low concentrations of the probes were used (≤10⁻⁶ M), so the pyrene dimmers and excimers were formed only intramolecularly. The ratios of excimer to monomer fluorescence intensities at excitation wavelength of 360 nm (where mainly the ground state pyrene dimmers are excited) were studied as a function of time. Different evolutions of these ratios were observed, which allowed us to predict that the silica structure developsvia the formation of primary particles, even at pH values below the isoelectric point of silica, where it is not possible to directly detect their formation.     

The modulation of face-face π-π interactions in Lewis acid catalysis

The enantiomeric excess observed for the exo-adduct from the Lewis acid catalysed Diels-Alder reaction between cyclopentadiene and methacrolein can be increased up to 21% by simple modification of the electronics of the aromatic ring in a series of stilbene-derived diol ligands, suggesting that the proposed face-face π-π interaction between the catalyst and the dienophile can be modulated by altering the electron density on the aromatic ring.     

Molybdenum(VI)-complexes with chiral N,O-ligands derived from carbohydrates: synthesis, structure and catalytic properties in asymmetric olefin epoxidation

Novel chiral 2′-pyridinyl alcohols derived from isopropylidene-protected carbohydrates are reported. They show different characteristics at the hydroxy group, but are all suitable ligands for chiral molybdenum(VI) complexes of the type MoO₂L₂ (L = chiral 2′-pyridinyl alcoholate). MoO₂(acac)₂ served as starting material in the complex syntheses. The structure of one ligand and one dioxo complex were exemplary established by X-ray crystallography. For catalytic runs in the enantioselective epoxidation catalysis trans-methylstyrene was used as model substrate, tert-butylhydroperoxide and cumolhydroperoxide, resp., as the oxidant.     

Improvement in steroid screening for doping control with special emphasis on stanozolol

The Medical Commission of the International Olympic Committee forbids the use of anabolic androgenic steroids and beta2-agonists to improve athletic performance. In this work we have selected examples of anabolic androgenic compounds and their metabolites to evaluate the GC-MS analysis of some trimethylsilyl derivatives. The aim is to set the best GC conditions to improve the detection within the whole range of analyte elution temperatures. The initial column temperature was changed to 105 or 140 degrees C followed by 40 degrees C min(-1) to 200 degrees C and then 15 degrees C min(-1) to 300 degrees C. Using 140 degrees C as the initial oven temperature it was possible to obtain narrower initial analyte distributions for the compounds that elutes at the beginning of the chromatogram as clenbuterol, mabuterol, epimethylenediol and norandrosterone, without loss of derivatized metabolites signal. Later. eluting analytes, such as the stanozolol metabolites, furazabol and oxandrolone were not affected. Temperatures below 140 degrees C. resulted in partial derivatization for some analytes mainly stanozolol related structures. Therefore evaluation of derivatization conditions as occurring in three steps, the vial, vaporization chamber and capillary column, was thoroughly assessed. The new program temperature improves the signal-to-noise ratio for some compounds and shows adequate resolution for endogenous compounds. Some of the difficult key separations necessary for doping control enforcement were also obtained with the proposed method.