Coinjection

In most cases these flow markers are species that are mixed with the sample and coinjected with the analyte onto the GPC column. The retention time of this marker is used to adjust the time axis to compensate for any moderate pump variability during the running of the standards and the samples. 

It is not common practice, but quite viable, to inject the flow marker at a predetermined volume offset from the polymer injection. This can be accomplished either with a second injection at a predetermined time into the run or by having two coordinated injection valves separated by a fixed volume of tubing. This approach can avoid many of the pitfalls described earlier. However, the mathematics of this correction is slightly different from that for a coinjected marker. The proper correction for the delayed volume injection is shown in Eq. (3) ... 

The difference between these two equations dictates that there will be an error if the coinjection equation is used for a delayed injection marker. Table 19.2 shows several examples and the magnitude of the errors generated. 

Corrected sample retention times Delayed injection calculation Coinjection calculation % difference... 

With the growth of plastic use in containers and packages, requirements to make them more compatible or useful resulted in new developments occuring and continue to occur. The two major approaches for providing permeability resistance in plastic containers involve chemically modifying the plastics surfaces and, more important from a marketing standpoint, the use of barrier plastics with nonbarrier types to meet cost-to-performance requirements. This is achieved through coextrusion, coinjection, corotation, and other such processes (Chapter 8). 

A similar problem is presented by vehicle tires and certain blow molded bottles, which must be virtually impermeable to air and other gases. An example of the use of a very impermeable elastomers is butyl rubber. Because of its impermeability to gases, butyl rubber is used as a roof coating. With plastic bottles, different layers of both coinjected and coextruded plastics (Chapter 8) can be used to fabricate the bottle to make it impermeable to different vapors and gases depending on the barrier plastic included. 

Plastic products are made by a variety of basic manufacturing processes. As an example a major method such as extrusion has subdivisions that include profile, pipe, tube, film, sheet, coating, post forming, etc. equipment In injection molding there are subdivisions such as coinjection, gas assist, foam, inmold decorating, etc. equipment. There are literally hundreds of processes used with only about the dozen, as reviewed in this chapter, that are principally used (2). 

The basics observed in molded products are always the same only the extent of the features varies depending on the process variables, material properties, and cavity contour. That is the inherent hydrodynamic skin-core structure characteristic of all IM products. However, the ratio of skin thickness to core thickness will vary basically with process conditions and material characteristics, flow rate, and melt-mold temperature difference. These inherent features have given rise to an increase in novel commercial products and applications via coinjection, gas-assisted, low pressure, fusible-core, in-mold decorating, etc. 

Coinjection molding Coinjection molding produces products that can help one... 

The recycled plastic will also have a degree of different contaminants that would eliminate its use in certain devices or products, such as in medicine, electronics, and food packaging. However, within these market applications there are acceptable designs with three-layer coextruded, coinjected, or laminated structures having the contaminated plastic as the center layer, isolated by clean plastics around it and no migration occurring. 

Analysis and purification of the product solution is best accomplished by gas chromatography. The submitters used a 500 cm. by 0.6 cm. aluminum or polyethylene column packed with 21% oxydipropionitrile on Chromosorb P with column, injector and detector operated at 25° and a flow rate of 50 ml./minute. Under these conditions the retention times of bicyclopentene and cyclopentadiene were 3 and 5 minutes, respectively, beyond that of the coinjected air. Since bioyclo-pentene is extremely labile with respect to acid catalysis any contact with water, hydroxylic solvents, and nonprotic acids should be avoided (Note 11). Bicyclopentene stored at —78° in anhydrous tetrahydro-furan is stable indefinitely. 

In a recently pnblished example of betaxanthin analyses in a complex food matrix, 19 betaxanthins were assigned in yellow Swiss chard petioles. Mass spectrometric measnrements are even more helpfnl if nnknown betacyanin structures are to be elucidated. While betacyanic plant materials such as red beet and amaranth may still be commercially available for coinjection experiments and comparison with samples under investigation, it may be an easier task to first optimize pigment separation followed by mass spectrometric measurements. 

Waste gas from produced hydrocarbons can be safely disposed by reinjecting into a formation. The waste gas is mixed with a surfactant to form a foam that, in turn, is placed within a disposal zone of a subterranean formation. The waste gas is trapped within the foam, thereby reducing the mobility of the gas in the formation, which, in turn, restricts the ability of the waste gas to readily flow out of the disposal zone and into the producing zone of the formation. The waste gas foam can be placed into the formation by coinjecting the surfactant and the waste gas, or it can be formed in situ by first injecting the surfactant and then injecting the waste gas [1356]. 

Coinjection of a low-concentration surfactant and a biopolymer, followed by a polymer buffer for mobility control, leads to reduced chemical consumption and high oil recovery. There may be synergistic effects between the surfactant and the polymer in a dynamic flood situation. The chromatographic separation of surfactant and polymer is important to obtain good oil recovery and low surfactant retention [1721],... 

The coinjection of growth-effective nutrients into the extreme environments that characterize petroleum reservoirs [1604]... 

More recently, coinjection of T7- or SP6-driven cDNA and T7- or SP6-RNA polymerase, respectively, into the cytoplasm achieved high levels of expression for some proteins, and may serve as an alternative to other techniques (Geib et al, 2001). 

Geib S, Sandoz G, Carlier E, Cornet V, Cheynet-Sauvion V, De Waard M. 2001. A novel Xenopus oocyte e3q>ression system based on cytoplasmic coinjection of T7-driven plasmids and purified T7-RNA polymerase. Receptors Channels 7 (5) 331. 

Multilayered articles can be made by coinjection blow-molding or coextrusion methods. A three-layer system generally contains a barrier layer sandwiched between two exterior layers. These are actually laminar products. In the coextrusion sequence, several extruders can be used to place the material into the mold. The multilayer container is then produced from blowing air into the preform. 

Stractures of 3-alkyl-5-methylindolizidines, found in thief ants, Solenopsis species (Table II), arrived at by gas chromatographic and mass spectral analysis were confirmed by coinjection and direct comparison with the synthetic sample. Indolizidine 15a from S. conjurata exhibits characteristic peaks at miz 152 (M — CHj) and 138 (M — C2H5, a base peak) as well as a parent peak at m/z 167 in the mass spectram. It corresponds to an isomer of 3-ethyl-5-methylindolizidine (15) which was prepared as a mixture of four stereoisomers by reductive amination of triketone 391 with ammonium acetate-sodium cyanoborohydride and sodium borohydride (Scheme 47). 

Intramuscular and subcutaneous injections are by far the most common means of parenteral drug administration. Because of the high tissue blood flow and the ability of the injected solution to diffuse laterally, drug absorption generally is more rapid after intramuscular than after subcutaneous injection. Drug absorption from intramuscular and subcutaneous sites depends on the quantity and composition of the connective tissue, the capillary density, and the rate of vascular perfusion of the area. These factors can be influenced by the coinjection of agents that alter local blood flow (e.g., vasoconstrictors or vasodilators) or by substances that decrease tissue resistance to lateral diffusion (e.g., hyaluronidase). 

Using a chiral column, coated with a definite modified cyclodextrin as the chiral stationary phase, the elution orders of furanoid and pyranoid linalool oxides are not comparable [11, 12]. Consistently, the chromatographic behaviour of diastereomers and/or enantiomers on modified cyclodextrins is not predictable (Fig. 17.1, Table 17.1). Even by changing the non-chiral polysiloxane part of the chiral stationary phase used, the order of elution may significantly be changed [13]. The reliable assignment of the elution order in enantio-cGC implies the coinjection of structurally well defined references [11-13]. 

Using amylose tris-3,5-dimethylphenylcarbamate as the chiral selector in enantioselective high-performance liquid chromatography, micropreparative resolution of the DHA racemate was achieved and the chromatographic behaviour in enantio-GC could be defined by coinjecting these references of definite chirality (Fig. 17.4) [13]. 

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