Determination of low levels of polymer additives migrating from polypropylene to food simulated liquids by capillary SFC and solvent venting injection

Summary Methods for the determination of specific migration of polymer additives from polypropylene to aqueous acetic acid and isooctane have been studied. The migrants were extracted from aqueous acetic acid and characterized by supercritical fluid chromatography (SFC) with flame ionization detection (FID) and mass spectrometry (MS). The isooctane simulant was concentrated and injected directly into the SFC. Injection of extracts after incubation, using the solvent venting injection technique in the SFC, enabled additive concentrations as low as 10 ppb in 150 ml simulant to be determined, corresponding to a specific migration level of approximately 1 g additive/dm² polymer.     

超临界流体萃取-胶束电动毛细管色谱法分离测定大黄中蒽醌类组分的含量

采用ＳＴＥ－ＭＥＣＣ法分离测定大黄中的芦荟大黄素，大黄素和大黄酸。萃取条件为压 力４１．４ＭＰａ，温度５０℃，改性剂量０．４ｍＬ。被测组分在１０ｍｉｎ得到全部分离。本法准确、简 便、快速、结果令人满意。     

无保护流体室温燐光法测定吲哚-3-丁酸的研究

在仅以碘化钾为重原子微扰剂、亚硫酸钠为除氧剂及无任何保护性介质存在的水溶液中 ,吲哚_3_丁酸 (IBA)能发射很强的室温光 (RTP) ;详细研究了分析测定条件及有机溶剂对RTP的影响 ;在最大光波长λex/λem =281/447nm处 ,光强度与IBA浓度在2.0×10 -7～1.0×10 -5mol/L范围内呈良好的线性关系 ,检出限4.3×10-8 mol/L ;方法直接用于强化水样和土壤中IBA的测定 ,回收率96 %～104 % ,相对标准偏差2.37 %～3.97 %。     

Synthesis of siloxane stationary phases for capillary gas chromatography and supercritical fluid chromatography

A comparison is made between dichlorosilanes and cyclic siloxanes as starting materials in the synthesis of stationary phases for capillary gas chromatography (CGC) and supercritical fluid chromatography (SFC). Siloxanes containing one or more of the side groups methyl, vinyl, phenyl, and cyanoethyl in various ratios were synthesized and compared. These phases were characterized by chromatographic (gel permeation, GPC), spectroscopic (IR, ¹H NMR, ²⁹Si NMR), and thermal (DSC) methods. Coated fused silica columns were evaluated with respect to polarity, crosslinkability with several free-radical initiators, and thermal stability. A new liquid phase, 7% cyanoethyl, 7% phenyl, 1% vinyl methyl polysiloxane is shown to be more polar than OV-1701, more temperature stable, easily crosslinked and suitable for use in supercritical fluid chromatography.     

Synthesis and characterization of monodisperse magnetic composite particles for magnetorheological fluid materials

Monodisperse magnetic composite particles (MCP) were prepared and characterized for a study of magnetic field-responsive fluids. Magnetic composite particles used are iron oxide-coated polymer composite particles, which were synthesized through in situ coating of iron oxide onto pre-existing polymer particles by the reduction of ferrous fluids. For a uniform and bulk coating of iron oxide, the porous structure was introduced into the substrate polymer particles through a two-step seeded polymerization method. Moreover, surface cyano-functionality was born from acrylonitrile unit of substrate polymer and it played an important role in obtaining successful uniform coating. The structure of the composite particle was analyzed by using a thermo gravimetric analysis (TGA) and a X-ray diffraction (XRD) analysis. The magnetization property of the particle was also observed. Then, the rheological properties of monodisperse magnetorheological (MR) suspensions of magnetic composite particles were examined under a magnetic field using a parallel-plate type commercial rheometer. From the rheological measurements, it was found that MR properties of the magnetic composite suspensions are dependent on the iron oxide content and the fluid composition.     

Unified gas and supercritical fluid chromatography on 50 μm i.d. Columns

A unified approach to sequential gas and supercritical fluid Chromatography using 50 μm i.d. open tubular columns is described. Sample introduction is performed by means of a rotary injection valve. In order that linear velocities can be optimized independently, a second rotary valve in the chromatographic oven is used to direct the flow of column eluate to the flame ionization detector through either fused silica tubing in GC, or a frit restrictor in SFC. Applications of sequential GC-SFC on a 50 μm i.d. open tubular column are demonstrated, and comparisons made between sequential GC-SFC on 50 and 100 μm i.d. columns.     

Differences in the electrorheological response of a particle suspension under direct current and alternating current electric fields

We have observed an unusual reduction of shear stress with increasing shear rate under direct current electric fields, for an electrorheological fluid composed of sulfonated poly(styrene-co-divinylbenzene) particles dispersed in silicone oil. At all shear rates, the shear stress under the electric field is larger than that in the absence of the field, indicating that there is still some field-induced agglomeration of the particles. In contrast, the behavior under alternating current electric fields is the Bingham-fluid-type response commonly observed with electrorheological fluids. It is suggested that the conventional dipole–dipole interaction approach based on simplified microstructural models would be unable to explain these phenomena. Received: 27 November 2000 Accepted: 22 May 2001     

The analysis of lubricating oil additives by supercritical fluid chromatography with packed and open tubular capillary columns

Lubricating oil additives have been analyzed by supercritical fluid chromatography on open tubular and packed capillary columns. Carbon dioxide and modified carbon dioxide were used as mobile phases and detection was accomplished by flame ionization and micro UV. Rapid and efficient analysis of the lubricating oil additives was demonstrated.     

Supercritical fluid extraction of oxadixyl from food crops

Summary This work describes the study of a degradation curve of Oxadixyl in field-treated potato and tomato samples. The residues were extracted using classical and supercritical fluid (SFE) extraction methods and analyzed by HRGC/ECD. The extraction techniques were compared and the results indicate the advantages of using SFE as an alternative method for pesticide analyses in these samples.     

Shear flow experiments in an assembly of gel beads and modelling of bingham behavior

In this paper, we present a rheological study of a compact layer of highly swollen gel beads. The flow regimes of these systems are modelled by an elastic sinusoid moving in a Newtonian fluid. This model predicts a yield stress varying with the square root of the elastic modulus of the gel bead. The slope at the origin (at zero velocity) of the flow curve is expected to depend only on geometrical parameters and on the solvent viscosity. The experimental data are in qualitative agreement with the theoretical predictions.