Analysis using hollow fiber

High-pressure gas separation, hollow-fiber membrane modules for, 15 823 High pressure liquid chromatography (hplc), 9 234 21 275 in herbicide analysis, 13 312 polymer analysis using, 19 566 High-pressure methanol, production process, 16 300-301 High pressure methods, specialized, 13 430-431... 

The process design principles of SLM, non-dispersive extraction, and hybrid hquid membrane systems need to be understood through bench scale experiments using feed solution of practical relevance. While the economic analysis of an ELM process can be performed from small scale experiments, such an analysis is difficult for other LM systems. In particular, availability and cost of hollow fiber membranes for commercial application are not known apriori. A simple rule of thumb for cost scale-up may not be apphcable in the case of an HE membrane. Yet we feel that the pilot plant tests would be adequate to make realistic cost benefit analysis of a liquid membrane process, since the volume of production in )8-lactam antibiotic industries is usually low. 

The use of membrane introduction mass spectrometry (MIMS) was first reported in 1963 by Hoch and Kok for measuring oxygen and carbon dioxide in the kinetic studies of photosynthesis [46], The membrane module used in this work was a flat membrane fitted on the tip of a probe and was operated in the MIS mode. The permeated anaytes were drawn by the vacuum in the MS through a long transfer line. Similar devices were later used for the analysis of organic compounds in blood [47], Memory effects and poor reproducibility plagued these earlier systems. In 1974, the use of hollow-fiber membranes in MIMS was reported, which was also operated in the MIS mode [48], Lower detection limits were achieved thanks to the larger surface area provided by hollow fibers. However, memory effects caused by analyte condensation on the wall of the vacuum transfer line remained a problem. 

Examples of the model considerations, presented below, can be regarded as simplified examples only. The processes have been studied using analytical [1] and numerical [27] solutions for both the local steady-state [1,2,69,70] and dynamic nonstationary [27,71,72] conditions, respectively. Both models, HLM [1] and MHS [27], with some modifications may be used for theoretical analysis of all OHLM systems. Considerations for hollow-fiber systems are presented also in a short. 

Eluents and regenerents suitable for the analysis of organic acids when applying an AFS-2 hollow fiber membrane suppressor are listed in Table 4-2. For the analysis of borate and carbonate with octanesulfonic acid as the eluent, an ammonium hydroxide solution with a concentration c = 0.01 mol/L can also be used as the regenerent. 

The CFS hollow fiber suppressor (see Section 3.4.3) that was developed for cation exchange chromatography can also be applied to cation analysis via ion-pair chromatography. It features good solvent stability and sufficient membrane transport properties for the anionic ion-pair reagent. This suppressor is regenerated with tetramethylam-monium hydroxide using a concentration of c = 0.04 mol/L. 

Abstract Thin and flexible probes made with hollow-optical fibers may be useful for remote spectroscopy. Experimental results showed that these probes are useful for endoscopic measurements of infrared and Raman spectroscopy. A hollow-fiber probe has been used for remote FT-IR spectroscopy in the form of endoscopic measurement of infrared reflectometry spectra inside the body. This measurement was made possible by the hollow-fiber probe s flexibility, durability, nontoxicity, and low transmission loss. A hoUow-fiber probe with a ball lens at the end works as a confocal system for Raman spectroscopy. It can thus detect the molecular structure of biotissues with a high signal-to-noise ratio. Owing to their small diameter, the probes are useful for in vivo, noninvasive analysis using a flexible endoscope. 

Recently, Psillakis et al. " have developed a liquid phase microextraction (LPME) technique using a hollow fiber membrane in conjunction with GC-MS for the extraction and analysis of phthalates. The resulting method was validated and compared with SPME. Both techniques showed comparable performance and were considered suitable for trace analysis of phthalates in water. 

Danesl and coworkers have developed a model for metal extraction using supported liquid membranes. Danesl et al. (74) included both Interfaclal reaction and boundary layers In their analysis. As they demonstrate, both effects can be Important. Recently, Danesl (75) developed a simplified model of metal extraction In hollow fiber membranes based on the model above. Danesl and Relchley-Ylnger (76) have expanded this model to Include deviations from a first order rate law. 

The techniques mentioned earlier are all characterized by liquid donor and acceptor phases. However, a gaseous acceptor phase is also possible, and that would be the most convenient and compatible arrangement for direct connection with GC. This is realized with the membrane extraction with a sorbent interface (MESI) technique. MESI can be used for either gaseous or aqueous samples, and the equipment employs a membrane module with a (usually) silicone rubber hollow fiber, into which the analytes are extracted from the surrounding liquid or gaseous sample. The carrier gas of a gas chromatograph flows inside the fiber and transports the analyte molecules as they are extracted from the membrane into a cooled sorbent trap where they are trapped. The analytes are subsequently desorbed from the sorbent trap by heating and are transferred to GC analysis. 

HFs have been used successfully for preconcentration in chemical analysis. One technique termed hollow-fiber liquid-phase microextraction (HF-LPME) involves filling the pores of an inert HF material (commonly polypropylene) with an organic phase containing a carrier in a similar way to the manufacturing of SLMs. The fiber is then dipped into an aqueous sample solution, and the analyte is transported across the HF to a small volume of receiver phase in the lumen of the HF that is subsequently analyzed [41,42]. 

Ding et al., confirmed the thermal treatment of precursor composite poly(amic acid) tertiary amine salts (PAAS) membrane using FT-IR/ ATR analysis at 150 °C, and obtained composite polyimide hollow fiber membranes. In their studies, the FT-IR spectroscopy effectively evaluated the imidization of the coating layer.Ii l... 

The use of evaporation to increase the driving force allows one to use a highly selective membrane and still retain a reasonable flux. However, evaporation complicates both the equipment and the analysis. Typical permeate pressures are quite low (0.1-100 Pa) tLeeper. 1992T Because of this low pressure, permeate needs a large cross-sectional area for flow or the pressure drop caused by the flow of the permeate vapor will be large. Thus, plate-and-frame, spiral-wound, and hollow fibers with feed inside the fibers are used commercially. Figure 17-13 shows that a vacuum pump and a condenser are required... 

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