Aqueous carrier

Zhang et al. [44] determined penicillamine via a FIA system. A 50 pL sample was injected into an aqueous carrier stream of a flow injection manifold and mixed with... 

Absorption Across the Skin. An aqueous carrier may be used for a variety of dermal products. In fact, carriers can be designed to limit the transportation of the penetration of the active ingredient (such as an insect repellent), if the desired effect is to keep the activity on the surface of the skin. Once again, however, only those materials that are dissolved will be available for penetration across the skin to gain access to the systemic circulation. For almost all chemicals in or about to enter commerce, dermal penetration is a passive process. The relative thickness of the skin makes absorption (into the systemic circulation) slower than the absorption across the GI or pulmonary barriers. This is compounded by the fact that the stratum comeum ftmction is to be impervious to the environment. One of the skin s major functions is protection from infection. Once a chemical penetrates into the dermis, it may partition into the subcutaneous fat. Essentially, absorption across the skin is a two-step process with the first being penetration and deposition into the skin and the second being release from the skin into the systemic circulation. The pattern of blood levels obtained via dermal penetration is generally one with a delayed... 

A typical extraction manifold is shown in Figure 13.2. The sample is introduced by aspiration or injection into an aqueous carrier that is segmented with an organic solvent and is then transported into a mixing coil where extraction takes place. Phase separation occurs in a membrane phase separator where the organic phase permeates through the Teflon membrane. A portion of one of the phases is led through a flow cell and an on-line detector is used to monitor the analyte content. The back-extraction mode in which the analyte is returned to a suitable aqueous phase is also sometimes used. The fundamentals of liquid liquid extraction for FIA [169,172] and applications of the technique [174 179] have been discussed. Preconcentration factors achieved in FIA (usually 2-5) are considerably smaller than in batch extraction, so FI extraction is used more commonly for the removal of matrix interferences. 

Recently, a miniaturized thermal apparatus, [t-ThFFF, was developed and applied to characterize the molar mass distribution of synthetic polymers in organic solvent as well to determine the particle size distribution of nanoparticles (PSs latex) in aqueous carrier. This 4-ThFFF proved to performed well in both macromolecule and particle analysis [48]. 

Sample dispersion is another cause of the long lag time in flow injection techniques where an aqueous carrier fluid is used [63,64]. Dispersion is caused by axial mixing of the sample with the carrier stream. This increases the sample volume, resulting in longer residence time in the membrane. Dilution reduces the concentration gradient across the membrane, which is the driving force for diffusion. The overall effects are broadened sample band and slow permeation. 

A cell stimulating composition for use in the treatment of infections comprising a water soluble chlorophyllin dissolved in an aqueous carrier. ... 

Although most applications of Fl-FFF have been reported for aqueous carrier liquids, a few studies have been carried out in organic liquids as well (for a more detailed discussion see also Sect. 4.3.1). Brimhall et al. [365,366] were the first to report non-aqueous polymer separations by Fl-FFF by separating polystyrene in ethylbenzene. Poly(ethylene oxide) and poly(methyl methacrylate) were characterized in THF [367] and, recently, a so-called universal fractionater also capable of high-temperature fractionations has been reported and applied to the separation of a variety of polymers and particles by Fl-FFF in non-aqueous carrier liquids, including the separation of polyethylene [368]. 

As the presence and duration of moisture on leaves has been shown to be critical in the germination and infection of several mycoherbicides (59,60,61,63), formulations are being developed that provide moisture and retard evaporation of water from the leaf surface (64). Quimby et al. (64) showed that without a dew period conidia of A, cassiae applied in an aqueous carrier alone and in an aqueous carrier followed by an overspray of an invert emulsion resulted in 0 and 88 percent mortality, respectively, in sicklepod seedlings. The development of this technology may provide a system to overcome some of the environmental constraints for mycoherbicide application that currently exist. 

In FLMs, a membrane aqueous carrier solution is circulated through a thin channel between two hydrophobic microporous membranes separating feed gas and sweep gas phases from the FLM phase. The stability of this membrane was reported to be 11 days without any decrease of flux. 

The sorbents most frequently chosen for current use are the porous silica derivatives. Most popular are the hydrophobic or "reverse phase" sorbents with bonded alkyl groups. These are ideally suited for the partly aqueous carrier phases that are suitable for separations related to the life sciences, an area that accounts for most of the current use of HPLC. 

FIGURE 8.14 Flow diagram of a flow injection system with wetting film extraction. S = sample C = aqueous carrier stream Org = organic solvent Ec = extraction coiled reactor SP = solvent added for single phase establishment Me — mixing coiled reactor D = detector. For details, see text. 

A wide range of internal lacquers developed for the heat processed food industry also find uses in the pharmaceutical and cosmetic field. The lacquers, which include acrylic, phenolics, polyesters, epoxy and vinyl resins, are normally applied via an organic solvent which is subsequently evaporated during curing. The use of aqueous carriers and powder coatings has also been developed. Ferrolite is a plastic coated metal using polypropylene, polyester, etc. 

The aqueous carriers were made from doubly distilled deionized water. Most of these carriers contained a surfactant (FL-70, Fisher Scientific, Fairlawn, NJ) and a bacteriocide (sodium azide, NaNa). 

Figure 4.29. FIA manifold for the determination of trace metals by solvent extraction with dithizone in carbon tetrachloride. The aqueous sample S is injected into the aqueous carrier stream AQ, to which at (a) the organic phase ORG is continuously added and after passing through the extraction coil (b), made of Teflon tubing, the organic phase is again separated at point (c) and carried on through the flow cell for spectrophotometric measurement.

In both commercial and home-built FIA instruments, the injection valve is made of PVC and/or Teflon, the coils and connecting tubes of polyethylene, polypropylene, or Teflon, and the pump tubes of PVC. All these materials are fairly resistant to polar solvents, and as long as aqueous solutions are used throughout, no problems will be encountered. Yet if nonpolar solvents have to be handled, such as in solvent extraction, it is necessary to use pump tubes resistant to these solvents [e.g., Acidflex or Viton tubes made of black flurorplast rubber, or the recently introduced Marprene tubes (see Table 5.1)], Teflon coils, and to construct the system so that the aqueous samples are injected into an aqueous carrier stream (i.e., the Perspex or PV(T made parts of the injection port do not contact the organic solvent). For FIA procedures performed exclusively in non-aqueous media, compatible materials have to be chosen carefully and the injection valve must be made entirely of Teflon or a stainless-steel-Teflon combination, such as that used in chromatographic valves. 

However, in most reported FI-AAS systems using on-line liquid-liquid extraction, the delivery mode b described in Sec. 3.4.6. involving a preliminary collection of the separated extractant in the loop of an injector valve is preferred. The collected fraction may then be presented to the nebulizer under optimum flow conditions either using a pumped aqueous carrier stream or simply by freely aspirated air-flow. The latter produced higher sensitivities, [14] probably owing to a further enhancement in the aspiration rate. 

Hilder E.F., Klampfl C.W., Buchberger W., Haddad P.R., Comparison of aqueous and non-aqueous carrier electrolytes for the separation of penicillin V and related substances by capillary elecfi-ophoresis with UV and mass spectrometric detection. Electrophoresis, 23,413- 20 (2002). 

After the injection valve, where the sample is injected into an aqueous carrier that can continuously merge with one or several reagent streams. This and another stream carrying an organic solvent converge in the extractor. Finally, the outgoing phase stream is monitored in a continuous fashion. 

Perman, C.A., Choi, H.-O. and Bartkus, J. (1998) Drug Loading of Polymer Substrates Using Supercritical Fluid Impregnation in an Aqueous Carrier Liquid, Proceedings of the 5 Meeting on Supercritical Fluids, Nice, pp. 379-385. 

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