Current methods of analysis for ethylene oxide (EO) in medical devices include headspace and simulated-use extractions followed by gas chromatography with either a packed or a capillary column. The quantitation limits are about 0.5-1.0 microg/g for a packed column and about 0.1-0.2 microg/g for a capillary column. The current allowable levels of EO on medical devices sterilized with EO gas as outlined in International Organization for Standardization (ISO) 10993-7 may be significantly reduced from current levels by applying the ISO Draft International Standard 10993-17 method for establishing allowable limits. This may require EO test methods with detection and quantitation limits that are much lower than those of the currently available methods. This paper describes a new method that was developed for the determination of low-level EO by solid-phase microextraction using the direct-immersion method. Factors such as temperature and stirring were found to affect absorption efficiency and absorption time. A low extraction temperature (about 6 degrees C) was found to be more efficient than room-temperature extraction. Stirring was found to reduce absorption time by about 50%. Under these conditions, detection and quantitation limits of 0.002 and 0.009 microg/g, respectively, were obtained by using a capillary column. As a result, this method makes compliance with lower EO limits feasible. 相似文献
A high-performance liquid chromatographic procedure was developed for the isolation and quantitation of coumarin from vanilla-based liquid flavorings of Mexican origin. Forty products representing fourteen different Mexican brands were assayed for coumarin, vanillin, and ethyl vanillin by the proposed method. The procedure has been adapted to the analysis of other products including domestic vanilla extracts and imitation vanilla flavorings for vanillin, ethyl vanillin, 4-hydroxybenzaldehyde and piperonal. Chromatographic retention data for thirty-seven compounds associated with vanillin and vanilla products employing two mobile phase systems are presented. 相似文献
A bioreactor configuration has been tested for simultaneous fermentation and separation of the desired inhibitory product, lactic acid. The bioreactor is a fluidized bed of immobilized Lactobacillus delbreuckii. Another solid phase of denser sorbent particles (a poly-vinyl pyridine resin) was added to this fluidized bed. These sorbent particles fell through the bed, absorbed the product, and were removed. In test fermentations, the addition of the sorbent enhanced the fermentation and moderated the fall of the pH. The biparticle fluidized-bed bioreactor utilizing immobilized microorganisms and adsorbent particles has been shown to enhance the production of lactic acid fourfold in this nonoptimized system.
Atomic fluorescence in flames is measured by an adaptation of a commercially available flame spectrophotometer. A study is reported of the effect of background radiation and source scattering on 3 flames, air-propane, air-hydrogen and air-acetylene, and of the effects of variation of fuel gas pressure, zone of measurement in the flame, analysing monochromator slit-width and wavelength of measurement. The air-propane flame appears to offer several advantages. The atomic fluorescence of 10 metals is described; those of Co, Fe and Mn have not been previously reported. Excitation of spectra is achieved by means of an a.c. xenon arc lamp or individual discharge lamps. 相似文献
Heterogeneous catalytic oxidation of a series of thioethers (2-thiomethylpyrimidine, 2-thiomethyl-4,6-dimethyl-pyrimidine, 2-thiobenzylpyrimidine, 2-thiobenzyl-4,6-dimethylpyrimidine, thioanisole, and n-heptyl methyl sulfide) was performed in ionic liquids by using MCM-41 and UVM-type mesoporous catalysts containing Ti, or Ti and Ge. A range of triflate, tetrafluoroborate, trifluoroacetate, lactate and bis(trifluoromethanesulfonyl)imide-based ionic liquids were used. The oxidations were carried out by using anhydrous hydrogen peroxide or the urea-hydrogen peroxide adduct and showed that ionic liquids are very effective solvents, achieving greater reactivity and selectivity than reactions performed in dioxane. The effects of halide and acid impurities on the reactions were also investigated. Recycling experiments on catalysts were carried out in order to evaluate Ti leaching and its effect on activity and selectivity. 相似文献
The preparation of five samples of poly(methyl methacrylate) covering a wide range of tacticity and their electron irradiation to produce series of varying molecular weight are described. The glass transition temperature Tg of each polymer was determined by DTA techniques. Plots of Tg and the reciprocal of the molecular weight are well fitted in every case by a straight line. The data are also fitted to the Gibbs-DiMarzio theory and the values of the energy and free-volume parameters obtained are discussed. A method of estimating Tg of pure syndiotactic poly(methyl methacrylate) by extrapolation is presented, the value obtained being 160°C. 相似文献
A detailed method for the routine preparation of glass capillary columns is presented. The method consists of coating a glass tube with quartz powder prior to pulling the tube into a capillary. The inner surface of the capillary consists of an even distribution of quartz particles fused to the walls. This surface has been found readily deactivated by standard procedures and ideal for the preparation of thick-film glass capillary columns. The method has been thoroughly tested in two independent laboratories to ensure that the procedures described are reproducible. 相似文献
A multiple time scale analysis of two four-variable models of the peroxidase-oxidase reaction, the DOP, and the Olsen model, is carried out. It is shown that autonomous limit cycle oscillations are exhibited by the fast subsets of these two models, but only in certain regions of parameter space, confirming the prior suggestion that the slow variable (NADH) is not essential for oscillatory behavior. However, it is found that the slow variable is essential for oscillatory behavior over other ranges of parameter values, and is always essential for complex oscillatory and chaotic behavior. This latter conclusion is based on a study involving driving the fast subset with a sinusoidally varying (NADH). This study suggests the level of coupling between fast and slow variables of an autonomous system necessary to cause the chaos observed in the DOP model. Further study of the driven system allows for the identification of a natural period of the nonoscillatory but bistable fast subsystem and a set of rules for applying a parametric driving in such a way as to generate a more complete Farey sequence from a truncated Farey sequence. These conclusions are used to compare the very similar DOP and Olsen models, which, nevertheless, exhibit quite different Farey sequences and routes to chaos. (c) 1995 American Institute of Physics. 相似文献