Propane/propylene separation by selective olefin adsorption on Cu/SBA-15 mesoporous silica

Samples of mesoporous silica, SBA-15, were prepared under hydrothermal conditions and Cu cations were incorporated into the framework by two different impregnation techniques. The corresponding adsorption/desorption isotherms of propylene, propane, and N₂ were measured to evaluate the material's effectiveness in the separation of propane/propylene mixtures. Adsorption uptake of propylene increased and that of propane decreased in Cu containing samples as compared to the uptakes observed in undoped SBA-15 samples. It was demonstrated that the presence of Cu atoms in the adsorbent lattice led to a greater selectivity towards propylene. Furthermore, the highest level of Cu(I) were obtained in samples prepared by equilibrium impregnation, which in turn improved the olefin/paraffin uptake ratio. Under some working conditions, the amount of propylene adsorbed in selected samples is totally reversible while propane uptake was negligible.     

Binuclear Cu2+ complex mediated discrimination between L-glutamate and L-aspartate in water

L-glutamate and L-aspartate selectivity is achieved by the action of two Cu2+ metal ions rightly disposed in a cyclophane-type macrocyclic framework; electrochemical sensing of glutamate has been achieved by adsorption of the copper complexes on graphite electrodes.     

Estimation of diuretic drugs in biological fluids by HPLC

Summary This critical review of different methods proposed for the determination and screening of diuretics is directed mainly, because of its potential application, towards highperformance liquid chromatography.     

Multiparametric curve fitting-I Computer-assisted evaluation of chelatometric titrations with metallochromic indicators

A curve-fitting procedure has been developed for the photometric complex-formation titration of the metal-indicator complex MIn(N) which is assumed to predominate in solution. By means of a least-squares procedure the following five parameters were determined: the end-point, the absorbance of the indicator complex A(M)XXX. the indicator concentration CXXX, the stability constants and, if possible, k(MY) . A modified version of Sillen's Letagrop Vrid has been used for the mathematical-statistical approach of the non-linear model based upon the non-transformed function A = f(v). Additional information is obtained about the goodness of fit, indicating whether the chosen model with predominance of MIn(N) is correct or not. The use of the program is demonstrated by application to chelatometric microtitrations of zinc and lead with EDTA, using Naphthylazoxine 6S and SNAZOXS as metallochromic indicators.     

Stereospecific total synthesis of (±)-strempeliopine

The 18-methylene-1,2-dehydroaspidospermidine (III) was stereospecifically transformed into the schizozygane alkaloid strempeliopine (II) in 16,6 % overall yield.     

Simultaneous determination of butyltin and phenyltin species in sediments using ultrasound-assisted leaching

A fast and simple procedure is presented for the simultaneous leaching of butyl (mono, di and tributyl) and phenyl organotin species from sediment samples. Leached compounds are further ethylated with sodium tetraethylborate in aqueous medium, and analyzed by gas chromatography. After testing the stability of triphenyltin under different extraction conditions, ultrasound-assisted leaching at room temperature in the presence of acetic acid was been proposed as an extraction procedure compatible with the simultaneous determination of phenyl- and butyltin compounds in sediments. Recoveries between 70 and 90% were obtained for phenyl species in spiked samples prepared in the laboratory. Results for butyltin species were validated by use of the reference material PACS-2. Quantification limits, using GC-MIP-AES as measurement technique, were approximately 5-10 ng g(-1). Precision in the consecutive analysis of three sediment samples varied between 3 and 10%.     

Osmotic behavior of a Nafion membrane in methanol-water electrolyte solutions

In this paper, an experimental study was carried out in order to investigate the osmotic transport of methanol-water electrolyte solutions through a Nafion membrane. The experimental data indicated that the Nafion membrane showed the typical anomalous osmotic behavior of charged membranes. The influence of some relevant parameters, such as electrolyte concentration difference, weight fraction of methanol on solution, and nature of cation was considered. The results showed that the osmotic volume flow was decreased with the presence of methanol on solvent, but did not alter the anomalous osmotic behavior of the membrane.     

Rapid and simple method for determination of Nepsilon-(carboxymethyl)lysine and Nepsilon-(carboxyethyl)lysine in urine using gas chromatography/mass spectrometry

A new procedure was developed to determine in urine the concentrations of N(epsilon)-(carboxymethyl)lysine (CML) and N(epsilon)-(carboxyethyl)lysine (CEL), the major products of oxidative modification of glycated proteins, to assess levels of oxidative stress in physiological systems. The urine samples were acetonitrile-deproteinized, then derivatized by ethylchloroformate, and N(O,S)-ethoxycarbonyl ethyl esters of amino acids were analysed by isotope dilution gas chromatography/mass spectrometry. Recovery averaged 89%. Linearity was excellent (r = 0.998-0.999) in the 0.5-25 micromol/L range for CML and CEL. The limit of detection of this assay was 0.1 micromol/L (corresponding to 0.20 pmol of CML or CEL on column). Intra-day and inter-day precisions were likewise excellent, with relative standard deviations <4.63 and <6.15%, respectively. Accuracy of CML and CEL determination (15 micromol/L) was 2.9 and 5.9% of the estimated theoretical value. The time from obtaining the urine sample to determination of the concentration from the chromatographic peak was 80 min or less. This method is sensitive, reproducible, accurate, relatively cheap and very simple. It can be useful for laboratories involved in the diagnosis and monitoring of age-related chronic diseases.     

Utilization of zirconia stationary phase as a tool in drug control

Zirconia-based stationary phases represent an interesting alternative to silica-based materials. Two zirconia-based stationary phases were studied as an option for use in drug analysis. The different properties of zirconia material, distinct from RP silica-columns, were employed for the development of a novel and rapid stability monitoring HPLC method. This method enables simultaneous control of possible degradation processes of active substance (ibuprofen) as well as antimicrobial excipients (methyl-and propylparaben). The separation of ibuprofen, its two main degradation products 2-(4-isobutyrylphenyl)propionic acid and 4-isobutylacetophenone, parabens, and 4-hydroxybenzoic acid as their degradation product was successfully accomplished on a Zr-CarbonC18 column using a mobile phase consisting of acetonitrile-phosphate buffer (pH 4.8)-propan-2-ol (27:56:17, v/v/v). Detection was performed at 258 nm and the analysis was completed within 17 minutes.     

Interaction of long chain alkylammonium cations with reduced charge montmorillonite

Reduced charge montmorillonites (RCM) were prepared using lithium thermal treatment. The sorption of octylammonium (OA), dodecylammonium (DDA) and hexadecylammonium ions (HDA) on differently charged samples were studied. The amounts of DDA and HDA sorbed on each RCM exceed the cation exchange capacity (CEC) but that of OA exceeds only the CEC of samples with the lowest CEC. The sorption is affected not only by the layer charge but also by the formation of collapsed interlayer spaces in the lowest charged montmorillonites. X-ray measurements confirmed the decrease of the layer charge after lithium thermal treatment and the layer charge heterogeneity in RCMs.