Trapping permeation techniques

As in most Lepidoptera, spruce budworm males locate conspecific females by flying upwind along a pheromone plume. The blends and release rates of these pheromone components form an important part of a specific communication system for the species. Once the communication system of an insect is understood, especially the pheromone chemistry as it relates to male behavior, it can be used in a variety of ways. For example, pheromones can be used to detect the presence of an insect in an area, to remove males from a population by trapping or poisoning and in air-permeation techniques in which the controlled and continuous release of pheromone components in the forest can disrupt mating. The latter use of pheromones appears to alter the normal male behavioral responses to the natural pheromone (16). 

The titanosilicate version of UTD-1 has been shown to be an effective catalyst for the oxidation of alkanes, alkenes, and alcohols (77-79) by using peroxides as the oxidant. The large pores of Ti-UTD-1 readily accommodate large molecules such as 2,6-di-ferf-butylphenol (2,6-DTBP). The bulky 2,6-DTBP substrate can be converted to the corresponding quinone with activity and selectivity comparable to the mesoporous catalysts Ti-MCM-41 and Ti-HMS (80), where HMS = hexagonal mesoporous silica. Both Ti-UTD-1 and UTD-1 have also been prepared as oriented thin films via a laser ablation technique (81-85). Continuous UTD-1 membranes with the channels oriented normal to the substrate surface have been employed in a catalytic oxidation-separation process (82). At room temperature, a cyclohexene-ferf-butylhydroperoxide was passed through the membrane and epoxidation products were trapped on the down stream side. The UTD-1 membranes supported on metal frits have also been evaluated for the separation of linear paraffins and aromatics (83). In a model separation of n-hexane and toluene, enhanced permeation of the linear alkane was observed. Oriented UTD-1 films have also been evenly coated on small 3D objects such as glass and metal beads (84, 85). 

Three approaches in Ihe use of pheromones have appeared in the literature i I I use of traps haiteil with sexual atiriieiant material as a means lor monitoring the infestation of areas with select insects 12) similar use of traps, except on a massive scale, to attrael males (female sex pheromone used as bait) and to) "male confusion" technique, in which female sex pheromone is permeated in ihe air. frustrating the attempts of males to locale females. 

In an attempt to overcome the significant difficulties that the presence of water vapor poses to the analysis of very volatile compounds, purge-and-membrane extraction techniques have been developed that largely prevent the introduction of water into the analytical system. Typical implementations of this form of sample introduction have been called by its developers membrane extraction with a sorbent interface (MESI),97 or membrane introduction mass spectrometry (MIMS).98 " They are based on a silicone hollow-fiber membrane that is inserted into the sample to be monitored, and the passing of a certain volume of inert gas through the membrane. Volatile compounds permeate the membrane and are swept to the adsorbent trap from which they are desorbed into the GC. This method of sample introduction is particularly suited for field and process monitoring and for dirty samples, since it prevents any nonvolatile compounds from entering the analytical system.100... 

The glass transition (Tg) of the amorphous PVDF regions is in the range of -40 to -30°C, depending upon the sample and test method. Other sub-Tg transitions have been studied recently by dielectric relaxation spectroscopy (108). These studies also indicate correlations with other techniques and identify a 50°C molecular chain transition as probably related to the amorphous region at the surfaces of crystals (109). Permeation characteristics are very sensitive to these transitions as well as the usual environmental parameters (110). Water molecules trapped in the amorphous regions are monomeric, not associated and clustered as in the liquid state (111). 

Numerous analytical procedures based on continuous systems have been developed for determining total inorganic carbon (TIC), most of them coupling gas permeation with FIA. It involves online CO2 formation and diffusion through a semipermeable membrane from a donor toward an acceptor stream and the quantification of the trapped CO2. In this technique, the sample is injected into, or merged with, an acid solution stream to form carbon dioxide, which diffuses across a polytetrafluoroethylene (PTFE) or silicone-mbber membrane with plane or tubular geometry into a recipient solution [39-49]. The trapped carbon dioxide has been determined either by electrochemical or spectrophotometric detection. 

Current Methods for Composition Analysis. The most frequently used method for determination of permeate gas composition is gas chromatography (2-6). In addition to the gas chromatograph, other analytical techniques, such as a lone thermal conductivity detector, mass spectrometry, and confinement of the more condensable gas in a series of cold traps, can be employed (2,7-72). 

Here ri r]c is the relevant Miesovicz viscosity, and v is the velocity of the sphere. The situation is quite different for semi-infinite and finite barriers, where permeation is necessarily involved in the flow, leading to undulation of layers and arrays of defects. Since it is very difficult to trap and stabilize a sphere vdth a size smaller than the film thickness, as far as we know, the flow of smectics aroimd a sphere has never been studied experimentally. However, experiments when finite particles are moving in the liquid crystal medium, which is at rest far from the particles has been carried out very recently, and it was indeed found that the flow of beads in smectic A and smectic C liquid crystals is purely viscous at sufficiently high speeds. Such technique is analogous to the one-bead micro-rheology ° developed recently to monitor the mechanical properties of viscoelastic soft materials, especially biological systems. i... 

A number of researchers have studied high-efficiency membrane filtration techniques as they apply to surfacant micelles. This process is called ultrafiltration, microfiltration, and nanofiltration, depending on the pore size of the membranes. These techniques are applied both to isolation of surfactants themselves and, in micelle enhanced ultrafiltration, to separation of other compounds that are trapped in surfactant micelles so that they are too large to permeate the membrane (99). 

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