Search Results
Separations of nicotinic acid and its derivatives on different stationary phases (silica gel, a mixture of silica gel and kieselguhr, polyamide 11, and RP-18) have been compared. Relationships between R M values and mobile-phase composition were determined for ten nicotinic acid derivatives. The results can be used to predict conditions suitable for extraction of the derivatives of nicotinic acid investigated.
Abstract
Thermal analysis of polyester and polyamides based on vanillic acid derivative — terephthaloyl-bis-(3-methoxy-4-oxy benzoic) acid has been reported. Different behaviours with the appearance of the thermal degradation, stucturization and carbonization stages were detected. Thermochemical behaviour of polymers under investigation revealed that technical lignin derivative — vanillic acid are a promise for obtaining polymer materials with good properties.
Simple and rapid TLC and column chromatographic methods have been established for separation of luteolin-7-rutinoside and luteolin-7-neohesperidoside on polyamide. A flavonoid mixture was isolated from the butanolic fraction of a methanolic extract of leaves of Ligustrum vulgare L. HPLC analysis of the isolated mixture showed the presence of two compounds in a ratio of approximately 1:1. TLC and column separation was achieved on polyamide with CHCl 3 -MeOH-2-butanone-acetylacetone 9:4:2:1 as mobile phase. After successful separation, the isolated compounds were identified by UV, MS, and NMR spectroscopy and by acid hydrolysis then comparison with authentic samples. Luteolin-7-neohesperidoside was isolated from Ligustrum vulgare L. for the first time.
Study on curing of novolac epoxy resin
Polyamide hardener systems
The optimization of proportions of novolac epoxy resin, Dobeckot E4 and polyamide hardener, EH411 has been established by DSC and the data indicates that resin-polyamide, 100∶40 and 100∶50, appear to be optimum where ‘extent of cure’ is maximum. The kinetic parameters for these formulations have been evaluated using isothermal and dynamic modes by employing DSC.
The retention behavior of aclarubicin and doxycycline has been examined on silica gel 60 WF254s, RP-18 F254s, cellulose F, and polyamide 11 F254 TLC plates and on silica gel 60 F254 and RP-18 WF254s HPTLC plates. Wide-range (from 0 to 100%, v/v) mixtures of n-alcohols with dimethyl sulfoxide (DMSO), hexamethyldisiloxane (HMDSO), acetonitrile, and water were used as mobile phases. The effect of mobile and stationary phases on the chromatographic behavior of the compounds was studied.
A comparison of the chromatographic behavior of benzoic acids on normal (silica gel), reversed (RP-18), and polyamide-11 plates using thin-layer chromatography (TLC) with controlled gas phase inside the chamber has been performed. This variant of TLC is based on the use of a gas phase moving over the TLC plate for regulation of the stationary and mobile phases as well as the acid—base properties of analytes during the separation process. The feasibility of such an approach is illustrated by the separation of benzoic acid derivatives using carbon dioxide, ammonia, and acetic acid vapor. It was shown that a gradual change of mobile phase acidity makes it possible to enhance separation efficiency and selectivity, this effect being dependent on the type of the stationary phase. The most considerable change in the retention of benzoic acid derivatives was observed for normal-phase plates with silica gel or silica sol, or starch binders used as the stationary phase. An alteration of surface acidity for polyamide and RP-18 plates is not so pronounced as for silica gel ones so that a smaller change in chromatographic parameters of benzoic acid derivatives was observed.
Abstract
Positron lifetime spectra were measured as a function of the time for metallocene polyethylene (mPE), poly(methyl methacrylate) (PMMA), polyamide (PA), and polycarbonate (PC). A decrease in o-Ps intensity with the elapsed time was observed in mPE and PC measured at room temperature and in PMMA measured at 225 K. Formation of free radicals has been supposed to be one of the causes of this effect. The effect of maleic-anhydride (maH) grafted copolymers and its ionomers in mPE/PA blends was also studied. The change in the positron lifetime distribution with increasing maH and the ionomer content revealed an enhanced interaction between mPE and PA phase and the decrease of dispersed mPE particles, which reflected good compatibility of the blend.
A sensitive, reliable, and rapid densitometric high-performance thin-layer chromatography (HPTLC) method has been developed for the quantification of hydroxysafflor yellow A (HSYA) in safflower. Chromatographic analysis was performed using the methanol extract of safflower. Polyamide TLC plates were used with the solvent system containing 3.6% hydrochloric acid, methanol, and ethyl acetate (7:3:1, v/v). Densitometric analysis of HSYA was performed at the absorbance mode of 399 nm. This system was found to give compact and dense spots for HSYA (R F value of 0.60 ± 0.03). The method showed a good linear relationship in the range of 61.0– 79.3 ng with r = 0.9991. The limit of detection, limit of quantification, and average recovery were 59 ng, 169 ng, and >95%, respectively. The proposed validated HPTLC method is an easy-to-use, accurate, and convenient method that can be successfully used for the standardization and quality analysis of herbal materials with different species of safflower.
Chromatographic behavior in normal-phase thin-layer chromatography has been investigated for six atypical antipsychotic drugs (amisulpride, clozapine, olanzapine, quetiapine, risperidone, and ziprasidone). The drugs were separated on silica gel, alumina, NH 2 , CN, diol, and polyamide plates with mixtures of n -hexane and six polar modifiers (acetone, dioxane, diethylamine, ethanol, isopropanol, and tetrahydrofuran) as mobile phases. The linearity of relationships between R M and volume fraction of modifier, the logarithm of the volume fraction, the molar fraction, and the logarithm of the molar fraction was tested. The results usually fitted the Snyder-Soczewiński equation, with r > 0.9. The best separation was achieved on silica gel plates with ethanol- n -hexane, 1 + 1 ( v/v ), containing 1.5% aqueous ammonia, as mobile phase.
Preparation and investigations of polyimides III
Thermal investigation of the imidization of polyamide acid powders
Polyamide acid powders of pyromellitic dianhydride and 4,4′-diaminodiphenyl ether base were prepared in tetrahydrofuran, in the heterogeneous phase. The imidization of these powders was investigated by thermogravimetric, calorimetric and mass-spectrometric methods.
