Use of Database of Plots of Pesticide Retention (R F ) Against Mobile-Phase Compositions for Fractionation of a Mixture of Pesticides by Micropreparative Thin-Layer Chromatography

Relationships between R _F values and mobile-phase composition have been determined for urea herbicides and fungicides in normal-phase systems (NP) of the type silica-nonpolar or weakly polar diluent (heptane, toluene, diisopropyl ether) – polar modifier (ethyl acetate, tetrahydrofuran, dioxane, ethyl-methyl ketone and 2-propanol). These relationships constitute a retention database which has enabled to choose optimum systems for preliminary fractionation of a multicomponent mixture of pesticides by zonal micropreparative TLC. The mixture was applied from the edge of the layer in the frontal + elution mode which increased the separation efficiency because or displacement effects. The separated simpler fractions were applied to a silica plate and rechromatographed. The plate was videoscanned, furnishing a real picture of the plate showing preliminary separation of the simpler pesticide fractions. Complete separation of the fractions was carried out by two-dimensional thin-layer chromatography on plates with chemically bonded-cyanopropyl silica stationary phase using non-aqueous eluent in the first direction and aqueous reversed-phase eluent in the second direction.     

IR spectroscopic study of the conformational lability of 4′-ethyl-4-cyanobiphenyl

The conformational lability of 4-ethyl-4-cyanobiphenyl molecules in solid crystal (SC) and isotropic liquid (IL) states was investigated by IR spectroscopic techniques (experiment and theory). IR absorption spectra were measured at 28°C–95°C in the frequency range 400 cm^–1–4000 cm^–1. Spectrum simulation was performed using the fragment method with allowance for the conformational fluctuations of molecules. The experimental and calculated spectra were compared and analyzed, and it was shown that in the IL, the samples are mixtures of conformers. The temperature changes in the spectra in the stated range are caused by the conformational lability of molecules.Original Russian Text Copyright © 2004 by L. M. Babkov, I. I. Gnatyuk, G. A. Puchkovskaya, and S. V. TrukhachevTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 398–405, May–June, 2004.     

Synthetic tanning agents. Characterization,control of synthesis and assessment of correlations between product composition and taning properties by reversed-phase high performance liquid chromatography

Summary Gradient elution RP-HPLC has been applied to the separation of the constituents of synthetic tanning agents. Information obtained from the chromatographic results was used to assess the possibility of optimizing the conditions of synthesis, to find out the number of species formed and to make a start at correlating the composition of the tanning agents and their properties.     

Optimizing control of simulated moving beds--linear isotherm

A new optimization based adaptive control strategy for simulated moving beds (SMBs) is proposed. A linearized reduced order model, which accounts for the periodic nature of the SMB process, is used for online optimization and control. The manipulated variables are the four inlet flow rates, the outputs are the raffinate and extract concentrations. Concentration measurements at the raffinate and extract outlets are used as the feedback information. The state estimate from the periodic Kalman filter is used for the prediction of the outlet concentrations over a chosen horizon. Predicted outlet concentrations are the basis for the calculation of the optimal input adjustments, which maximize the productivity and minimize the desorbent consumption subject to constraints on product purities. The realization of this concept is discussed and the implementation on a virtual eight column SMB platform is assessed, in the case of binary linear systems. For a whole series of typical plant disturbances it is shown that the proposed approach is effective in minimizing off-spec products and in achieving optimal SMB operation, also in the case where there are significant model uncertainties.     

Simple and rapid micellar electrokinetic capillary chromatographic method for simultaneous determination of four antiepileptics in human serum

A very rapid and simple MEKC method was developed for the simultaneous determination of four antiepileptic drugs, ethosuximide (Etho), primidone (Pri), phenytoin (Pht) and carbamazepine (Cbz) in human serum. Sample analysis required only 100 microL of human serum which only needed to be centrifuged, decanted and combined with the running buffer [5.3 mM Na(2)HPO(4)/3.2 mM borax buffer (pH 9.5) containing 55 mM SDS and 3.5% (v/v) acetone]. The analysis was performed in only 10 min into fused-silica capillaries (57 cm total length with 50 microm i.d. and 50 cm to the detector) using the MEKC methodology with diode-array detection at 220 nm. The calibration graphs were established for ethoximide, primidone, phenytoin and carbamazepine between 0 and 20 mg/L. Recoveries were between 85 and 87%. The simplicity of the proposed methodology makes it suitable for routine clinical use, especially for epileptic patients on polytherapy.     

Determination of alcohol polyether average molar oligomer value/distribution via supercritical fluid chromatography coupled with UV and MS detection

Supercritical fluid chromatography (SFC) was used for the analysis of ethoxylated and propoxylated surfactants. Samples were derivatized to phenylated silyl ethers with a disilazane-chlorosilane mixture. Addition of a phenyl group to the surfactant allowed UV-absorbance detection of each oligomer. Acetonitrile and methanol were evaluated as mobile phase modifiers. Better peak shape was realized with methanol-modified CO2 on an octadecyl silica bonded phase than with acetonitrile-modified CO2. Peak assignments were made via SFC coupled with electrospray ionization-mass spectrometry (ESI-MS) in the positive ion mode. A sulfonamide-embedded alkyl stationary phase was also evaluated for separation of the derivatized samples. SFC-UV and SFC-ESI-MS data were jointly used for calculation of average molar oligomer values which were then compared to values calculated from 1H NMR data of non-derivatized samples. The derivatization or separation method using the sulfonamide embedded phase required no preliminary cleanup and yielded reproducible oligomer values that were consistent with those of the manufacturer's nominal values.     

Chemical thermodynamics

The curing of composition containing epoxy bond is complicated chemical and technological process where under temperature and pressure conditions a change of its structure occurs. The structure changes are possible to know by thermal methods as DSC, DTA, etc. and also by measurement of dielectrical response under the low frequency electrical field.     

Evaluation of micellar liquid chromatography and capillary zone electrophoresis for dope control in sport

Micellar liquid chromatography (MLC) and capillary zone electrophoresis (CZE) have been evaluated for the analysis of twelve banned drugs in sport including diuretics and -blockers. In MLC, a sodium dodecylsulphate aqueous solution has been used as mobile phase using an octadecylsilica column. In CZE, a pH 8 buffer solution and a silica capillary have been employed. Parameters of retention and efficiency have been compared. Limits of detection with UV detection at 254 nm and relative standard deviations for atenolol, furosemide, nadolol, spironolactone and triamterene were established and compared in both techniques. Examples of direct urine injection into the separation systems are presented. Drugs overlapping in MLC are well resolved in CZE, while the opposite is true for a limited number of drugs. Some interferences from urine may arise in CZE. The selectivity of analysis would be greatly enhanced by using both techniques, which require only filtration as pre-treatment.     

氧化钪中Ti,Mo,W,V,Zr等难熔杂质光谱分析

本用提高样品蒸发速率的方法提高氧化钪中难熔杂质光谱分析灵敏度。采用一种特殊的阴极设计，配合使用Ｎ２＋Ａｒ气氛控制，在旋流气室中放电激发，取样仅５ｍｇ的条件下，光谱测定氧化钪中难烷质Ｔｉ，Ｚｒ，Ｍｏ，Ｗ，Ｖ灵敏度可达（１－３）×１０＾－４％。测定的相对标准偏差为９％－２７％。     

水溶液中Mn2+对硫化锌纳米粒子形貌的调控作用

利用硫代乙酰胺在水溶液中缓慢释放的S2-与Zn2+反应制备了ZnS纳米颗粒,ZnS纳米颗粒沉积吸附在3-磺酸基丙基三甲氧基硅烷自组装单层膜上。 实验发现,溶液中添加少量Mn2+,可以显著影响ZnS纳米颗粒的形貌,对ZnS纳米晶的生长方向也有重要影响。 EDS和XRD谱证实Mn2+并没有掺杂到纳米颗粒中去。 这为纳米粒子形貌的调控提供了新途径。 并对ZnS的形成过程进行了探讨,并提出了可能的影响纳米材料形貌的机制。