Membrane extraction MIMS

The core development of MIMS has centered upon MS ionization techniques for the analysis of aromatic contaminants in water,47 improving membrane extraction selectivity48 and enhancing MIMS sensitivity by cooling and heating the membrane (trap and release MIMS).49 50 A dedicated review has been written on the applications of MIMS in environmental analysis.51... 

The use of silicone membranes as an interface in MIMS for direct extraction and analysis by MS has fostered their implementation for extraction purposes that can be combined off-line or on-line with other analytical instrumentation, such as GC. The technique of membrane extraction with sorbent interface (MESI) (Figure 4.2) employs the pervaporation principle in a nonporous polymeric membrane unit, where the membrane is used as a selective barrier for the extraction of VOCs and SVOCs in gaseous or liquid samples. 

The polymeric membrane extraction systems, that is, MIMS, MESI, and PIME, have been extensively applied for sampling VOCs and SVOCs. In contrast, liquid membrane extraction... 

Membrane SLM MESI MMLLE MIMS PME HF-LPME MASE LGLME Headspace-solid phase dynamic extraction (HS-SPDE) Purge-and-membrane extraction Headspace/membrane extraction w. sorbent interface (HS-MESI) Headspace/membrane inlet mass spectrometry (HS-MIMS)... 

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 greatest challenge in membrane extraction with a GC interface has been the slow permeation through the polymeric membrane and the aqueous boundary layer. The problem is much less in MIMS, where the vacuum in the mass spectrometer provides a high partial pressure gradient for mass transfer. The time required to complete permeation is referred to as lag time. In membrane extraction, the lag time can be significantly longer than the sample residence time in the membrane. An important reason is the bound-... 

A consequence of MESI application is the membrane introduction mass spectrometry system (MIMS), which allows selective extraction of VOCs and direct MS analysis without chromatographic separation. The gaseous substances permeate through the highly hydrophobic membrane and are introduced directly to a mass spectrometer [115-118]. 

MESI, TMD, and MIMS suffer from a limited range of applications limited to apolar volatile compoimds. The limitation results from the usage of PDMS-membrane. MESI, TMD, and P T were compared by Matz et al. [196]. P T offers a simple set-up, high throughput, and good sensitivity, but it suffers in poor extraction of polar compounds and the trapped water, which induces chromatographic problems. MESI does not suffer from trapped water, but its memory effect is its main drawback. On the other hand, TMD is adequate for polar compoimds and does not show the advantage of water exclusion. 

Epichlorohydrin is extracted from water by SPE on a Chromabond HR-P column. Purther analysis is by GC [39]. Johnson et al. [45] monitored online epichlorohydrin in water with liquid membrane introduction mass spectrometry (MIMS). 

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