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961.
López-Blanco MC Reboreda-Rodríguez B Cancho-Grande B Simal-Gándara J 《Journal of chromatography. A》2002,950(1-2):293-299
The electrophoretic behaviour of ionizable and neutral alkylxanthines commonly used in pharmaceutical preparations was studied. The performance of various separation modes including capillary zone electrophoresis (CZE), cyclodextrin electrokinetic chromatography, and micellar electrokinetic chromatography (MEKC) with either sodium dodecyl sulfate (SDS) or bile salts as surfactants, was assessed. CZE in an alkaline medium successfully separates ionizable xanthines and dyphylline. The addition of carboxymethyl-β-cyclodextrin to the background electrolyte allows only partial resolution of neutral xanthines. Based on MEKC results, bile salts exhibit more discrimination ability than SDS to separate similar xanthines. The best results are provided by taurodeoxycholic acid, which ensures baseline separation of xanthines. 相似文献
962.
J. López-Cervantes D.I. Sánchez-Machado J. Simal-Lozano P. Paseiro-Losada 《Chromatographia》2003,58(5-6):321-326
Summary A high-performance liquid-chromatographic method with UV detection (HPLC–UV) has been developed for quantification of ethylene terephthalate oligomers in olive oil, from which they were extracted with acetonitrile. Oligomers, from monomers (M1) to pentamers (M5), were jointly and/or individually identified by liquid chromatography with mass spectrometry (electron-impact mass spectrometry (EIMS) low- and high-resolution) and were quantified by HPLC–UV using an acetonitrile solution of the major oligomer (the trimer M3) as standard. For M3 recovery was 98.9%, the detection limit was 60 g L–2, and method precision was 2.03% (RSD). Migration of oligomers M1–M5 into 50 mL olive oil sealed in each of two brands of 10 cm × 10 cm poly(ethylene terephthalate) roasting bag was evaluated under two sets of conditions that approached but remained below the limit at which the bag material became physically deformed – heating for 7 min at 850 W in a microwave oven, or for 60 min at 200 °C in a conventional oven. Total migration was approximately 2.7 mg dm–2 under the former conditions and 3.5–4.1 mg dm–2 under the latter.Presented at the International Symposium on Separation and Characteristics of Natural and Synthetic Macromolecules, Amsterdam, The Netherlands, February 5–7, 2003 相似文献
963.
964.
On the structure formation of hydrophobed particles in the boundary layer of water and octane phases
Two-dimensional aggregation of the surface modified glass beads was carried out in the boundary layer of water and octane phases. The effect of particles' hydrophobicity was investigated on the structure of forming aggregates and the growth process. The structure of the aggregates and their growth were characterized by a density function which demonstrates the change of mean particle density as a function of aggregate size. The growth yielded fractal or nonfractal structures in the investigated systems. The fractal structure of the aggregates was observed to be dependent on restructuring processes controlled by the surface properties of the beads.The experimental results are compared with earlier findings for aggregation of hydrophobic beads in the boundary layer of water and air phases.On leave from Loránd Eötvös University, Budapest, Hungary 相似文献
965.
Summary Reinvestigation by HPLC of the petals ofLilium tigrinum and the isolation of some minor compounds is reported. Using HPLC-controlled, preparative-column chromatography, 5,6-diakarpoxanthin
(6), 6-epikarpoxanthin (2), 5,6-diacapsokarpoxanthin (8), and 9Z-antheraxanthin (9Z-13) were isolated and characterized. Based on spectroscopic data the absolute configurations of6 and8 were identical with those originating from paprika, thus the 5,6-diakarpoxanthin (6) and 5,6-diacapsokarpoxanthin (8) have the 3S, 5S, 6S configuration and 6-epikarpoxanthin (2) has the 3S, 5R, 6S configuration.
Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997. 相似文献
966.
López-Hernández J González-Castro MJ Pereda-González M 《Journal of chromatographic science》2000,38(9):383-385
A high-performance liquid chromatographic method using refractive index detection for the determination of glycogen in sea urchin (Paracentrotus lividus) gonads is developed. After alkaline digestion with sodium carbonate, samples are adjusted to pH 4.6 with citric acid and incubated with amyloglucosidase to hydrolyze the glycogen. The resulting glucose is determined using a Spherisorb NH2 column as the stationary phase and an acetonitrile-water mixture (80:20, v/v) as the mobile phase. The relative standard deviation (%) was 3.57, the limit of detection was 40.1 microg/mL, and the recovery percentage was 97.2%. 相似文献
967.
Otón F Tárraga A Velasco MD Molina P 《Dalton transactions (Cambridge, England : 2003)》2005,(7):1159-1161
A ferrocene-based heteroditopic receptor containing urea and crown ether units shows electrochemical responses to dihydrogenphosphate and fluoride anions. K+ cations can only be detected in the presence of dihydrogenphosphate. 相似文献
968.
The thermal characterization (DSC and TG) of benzylcellulose derivatives prepared from the benzylation of bleached Pinus Kraft
pulp is described in this paper. The objective of this study was to examine the changes in glass transition temperature (T
g) and the thermal stability of the benzylated product as a function of the benzylation extent (degree of substitution). The
DSC analysis showed that the benzylcelluloses can display glass transition temperature at two different regions and that thermal
stability is slightly higher than that of the parent cellulose.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
969.
As shown in this paper, multivariate calibration in general and principal component regression (PCR) in particular allow the determination of Captopril by differential pulse polarography (DPP) in the presence of oxygen despite the overlap between their polarographic bands. Electrochemical parameters (pulse amplitude, pulse delay and drop time) are optimized from response surfaces using PCR to determine the relationship between the variables to be optimized and the relative square error of prediction (RSEP), which was adopted as the parameter to be minimized. The proposed method is quite fast and inexpensive as a result of the decreased analysis times and sparing use of the inert gas. It was applied to the determination of Captopril in synthetic samples and a commercially available pharmaceutical preparation, with relative errors and confidence intervals <2.5% and 2.0%, respectively. It should be noted that the sample can be analysed directly following dissolution in water without the need to remove the excipients. 相似文献
970.
1,2,4-Thiadiazolo[2,3-a]pyridinium chlorides undergo a very facile base promoted transformation to give bispyridilimino-1,2,4-thiadiazolidines. The unequivocal structural assignment of these last compounds was achieved by spectroscopic 1H, 13C and 15N two dimensional methods. 相似文献