The use of chiral interaction reagents in the separation of D(−)-and L(+)-ascorbic acid by ion interaction reversed-phase HPLC

Summary An HPLC reversed-phase ion interaction reagent method is presented, which makes use of chiral compounds as the interaction reagents. By employing the optical isomeric forms of malic, tartaric and mandelic acids as the interaction reagents, a good separation of D(−) and L(+) ascorbic acid has been achieved. The method has also been applied to the identification of vitamin C in some medical formulations. The separation of te enantiomeric forms of DL malic acid has been attempted and a shor discussion is presented about the elution sequence in chromatographic separation of D- and L-enantiomers.     

Liquid chromatography of polymer mixtures by a combination of exclusion and full adsorption mechanisms. Three- and four-component polymer blends

Summary Coupling of full adsorption-desorption and size-exclusion chromatography (FAD-SEC) has been applied to the separation and molecular characterization of three- and four-component polymer blends. The method is based on the full adsorption of alln orn−1 components of the polymer blend in a specially designed FAD minicolumn. By appropriate eluent switching the adsorbed polymers are desorbed stepwise from the FAD minicolumn into an on-line SEC column for molecular characterization. It is shown that the desorption isotherms of particular blend components give valuable information about the appropriate displacer composition. The exact position of the desorption isotherms depends, however, both on the amount of polymer adsorbed and in the presence of other, chemically different, polymers within FAD column. The nature and composition of the displacer must, therfore, be adjusted if the intervals between the desorption of particular blend components are to be large enough to prevent displacement overlap. Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997.     

Synthesis of two new crown ethers containing selenium and the complexation of one of them with silver and lead

Two new macrocyclic crown ethers containing one or two selenium donor atoms have been prepared. Diselena-18-crown-6 (2) was found to transport silver ions through a methylene chloride bulk membrane at about the same rate as the analogous dithia- (3) and diaza-18-crown-6 (4) compounds and transported lead ions about the same as dithia-18-crown-6 but better than diaza-18-crown-6.     

Fluorometric detection with a packed flow cell in micro high-performance liquid chromatography

Summary A packed flow cell was used for fluorometric detection in micro high-performance liquid chromatography. The flow cell consisted of fused-silica tubing packed with the same material as the separation column. A focusing effect of the stationary phase on the signal intensity was observed, leading to an improvement of the mass detection limit, as achieved by on-column detection.     

担体对Fe—MnO催化剂CO＋H2反应性能的影响

考察氧化物担体对Fe-MnO催化剂反应性能影响的结果表明,担体的类型对Fe-MnO催化剂CO加氢反应性能影响很大,其低碳烯烃选择性相差悬殊,Al_2O_3、SiO_2和MgO担载的Fe-MnO催化剂都不利于低碳烯烃的生成,而TiO_2担载的Fe-MnO催化剂则具有较高的烯烃选择性和催化活性。从担体-金属相互作用本质的差异,研究了担体对金属活性组分化学状态的影响及催化活性相与F-T合成烯烃的关系,发现担体-金属间的电子效应有利于催化剂活性和选择性的提高,其它物理化学效应引起的相互作用则不利于改善催化剂性能;还表明Fe_(?)C是催化活性相,Fe~(2+)物种的存在不利于提高烯烃的选择性。     

Efficient combination of task-specific ionic liquid and microwave dielectric heating applied to one-pot three component synthesis of a small library of 4-thiazolidinones

The first report of the use of task-specific ionic liquid as synthetic equivalent of ionic liquid-phase matrice for the preparation of a small library of 4-thiazolidinones is reported in this paper. The starting (ethyleneglycol)ionic liquid-phase is functionalized in good yields with 4-(formylphenoxy)butyric acid by using usual esterification reaction conditions (DCC/DMAP as catalyst). The synthesis of the ionic liquid-phase bound 4-thiazolidinones was performed by a one-pot three-component condensation under microwave dielectric heating. The final cleavage under microwave/catalysis strategy provides the expected 4-thiazolidinones in high purity after flash-chromatography purification. According to the ionic liquid-phase organic synthesis (IoLiPOS) methodology, it was found that optimized reaction conditions were performed by standard analytical methods (NMR, TLC). The ¹H, ¹³C NMR spectrum of some representative 4-thiazolidinones and ionic liquid-phase bound benzaldehyde are also reported.     

Determination of Lercanidipine Hydrochloride and Its Impurities in Tablets

The reversed-phase high-performance liquid chromatography (RP-HPLC) method was developed for determination of lercanidipine hydrochloride and its synthetic impurities, degradation and oxidative products in Carmen^® tablets. The best separation was performed on Zorbax SB C18 column, 250 x 4.6 mm, particle size 5 m. Acetonitrile-water-triethylamine 55:44.8:0.2 (v/v/v) was used as a mobile phase with flow rate 1 mL min^–1. pH was adjusted to 3.0 with orthophosphoric acid. UV detection was performed at 240 nm. Duration of chromatographic run was about 12 min for six examined compounds. The chromatographic conditions for the determination of lercanidipine hydrochloride and its related substances were the same, but the concentration of lercanidipine hydrochloride was 0.03 mg mL^–1 for assay and 0.3 mg mL^–1 for related substances. The validation of the method performance characteristics (figures of merits, quality of parameters) was established to be adequate for the intended use. The evaluation of number of parameters, such as selectivity, linearity, accuracy, specificity, precision (repetability and reproducibility), sensitivity and detection and determination limits is entailed.Acknowledgements This work was supported by the Institute of Pharmacy of Serbia, Belgrade and by the Ministry for Science, Technology and Development of Serbia, Contact: 1458     

Unique solvent effects on selective electrochemical fluorination of organic compounds

Recent studies on solvent effects on electrochemical partial fluorination are reviewed. At first, the historical background and some problems of electrochemical fluorination in organic solvents like acetonitrile (MeCN) are briefly mentioned. Ethereal solvents like dimethoxyethane (DME) and a mixture of DME and MeCN were found to improve both the yield and current efficiency for electrochemical fluorination since these solvent systems effectively suppress anode passivation and overoxidation of fluorinated products once formed during the electrolysis. It was also found that DME stabilizes radical cationic intermediates of 4-arylthio-1,3-dioxolan-2-ones and 3-phenylthiophthalide leading to α-fluorination while dichloromethane (CH₂Cl₂) destabilizes them leading to fluorodesulfurization. On the other hand, imidazolium ionic liquids and liquid fluoride salts like Et₄NF·4HF and Et₃N·5HF exhibited similar effects to CH₂Cl₂. Selective fluorination of hardly oxidizable phthalide was also achieved using a combination of two kinds of ionic liquids (imidazolium triflate and liquid fluoride salts).     

Swelling of physically cross-linked copolymers in water vapour

A general thermodynamic equation for the swelling of a cross-linked polymer system in the vapour of a swelling agent has been derived under isothermal and isobaric conditions. The equation is used to describe the equilibrium uptake of water by elastomers Arnitel^® (DSM), which are hard-soft-segment block copolymers in which the hard segments poly(butylene terephthalate) crystallise and are responsible for a physical cross-linking. The gravimetrically determined degrees of swelling of different elastomers in water vapour of various partial pressures are analysed and discussed by the application of an extended semi-empirical swelling equation of Flory-Huggins-Staverman-van Santen.