Membrane extraction gas injection

Kou, D., A. San Juan, and S. Mitra. 2001. Gas injection membrane extraction for fast on-line analysis using GC detection. Anal. Chem. 73 5462-5467. 

Gas injection membrane extraction (GIME) of aqueous samples has been developed to address the issues of boundary layer effects and sample dispersion [66]. This is shown in Figure 4.20. An aqueous sample from the loop... 

Figure 4.20. Schematic diagram of gas injection membrane extraction. (Reproduced from Ref. 66, with permission from the American Chemical Society.)...

In 1985, Ruzicka and Hansen established the principles behind flow injection optosensing [13-15], which has subsequently been used for making reaction-rate measurements [16], pH measurements by means of immobilized indicators [17,18], enzyme assays [19], solid-phase analyte preconcentration by sorbent extraction [20] and even anion determinations by catalysed reduction of a solid phase [21] —all these applications are discussed in Chapters 3 and 4. Incorporation of a gas-diffusion membrane in this type of sensor results in substantially improved sensitivity (through preconcentration) and selectivity (through removal of non-volatile interferents). The first model sensor of this type was developed for the determination of ammonium [13] and later refined by Hansen et al. [22,23] for successful application to clinical samples. 

For gas chromatography, the most suitable membrane extraction technique is MMLLE. The organic acceptor is better compatible with GC than with HPLC, as are the analytes that are best extracted in such a system, i.e., relatively hydrophobic compounds. A new development is the ESy instrument (ESyTech AB, Lund, Sweden) [76-78] where an MMLLE extraction in microscale (1 mL extracted into a volume ca 1 p,L) is automatically performed and the organic extract is directly injected into the GC by an injection needle, directly connected to the extraction cell. See Figure 12.7. 

Tecator Ltd. [16] have described a flow injection analysis method for the determination of 0.2 -1.4 mg/1 (as NH3N) of ammonia nitrogen in soil samples extractable by 2 M potassium chloride. The soil suspension in 2 M potassium chloride is centrifuged and filtered and introduced into the flow injection system for the analysis of ammonia (and nitrate) one parameter at a time. Ammonia is determined by the gas diffusion principle, in which a PTFE membrane is mounted in the gas diffusion cell. 

Hauser, B., P. Popp, and E. Kleine-Benne (2002). Membrane-assisted solvent extraction of triazines and other semi-volatile contaminants directly coupled to large-volume injection-gas chromatography-mass spectrometric detection. J. Chromatogr. A, 963 27-36. 

Hauser B. and P. Popp. 2001. Membrane-assisted solvent extraction of organochlorine compounds in combination with large-volume injection/gas chromatography-electron capture detection. J. Sep. Sci. 24 551-560. 

Iparraguirre, A., Navarro, P., Prieto, A., Rodil, R., Olivares, M., Fernandez, L.A., Zuloaga, O. Membrane-assisted solvent extraction coupled to large volume injection-gas chromatography-mass spectrometry for the determination of a variety of endocrine disrupting compounds in environmental water samples. Anal. Bioanal. Chem. 402, 2897-2907 (2012)... 

Morabito PL and Melcher RG. Automated membrane/gas chromatography system for extraction and determination of trace organics in aqueous samples using large volume injection. Process Control and Quality 1992 3 35 2. 

FigJ.15 Schematic diagram of an on-line FI sample cleanup system for a gas chromatograph. OR organic solvent S, aqueous sample SG, phase segmentor EX. extraction coil SP membrane phase separator W, waste DC. desiccator, V, 6-port injector valve B, heater SC. stopcock 1. injection port of gas chromatograph D. detector GC. gas chromatograph [54]. 

In order to automate the analysis, these methods frequently combine immobilized enzymes with flow or sequential injection techniques. These methods may include a separation step such as solid-phase extraction, gas diffusion, or pervaporation. The latter is a nonchromatographic separation technique, which selectively separates a liquid mixture by partial vaporization through a nonporous polymeric membrane. Separation is not based on relative volatilities as in distillation, but rather on the relative rates of permeation through the membrane. 

Two other methods have been approved by AOAC for determination of sulfites in food. One is a quantitative assay based on malachite green decolorization using flow injection analysis. Sulfite is released from a sample slurry with alkali, then the test stream is acidified to produce sulfur dioxide gas which diffuses across a Teflon membrane into a flowing stream of malachite green, and the extent of decolorization is measured at 615 nm. The other method is based on ion exclusion chromatography with sulfur dioxide being released by alkali extraction, and the diluted filtrate is injected onto an anion exclusion column linked to an electrochemical detector. 

See also Extraction Solvent Extraction Principles Solid-Phase Extraction Solid-Phase Microextraction. Flow Injection Analysis Principles Instrumentation. Ion Exchange Principles. Ion-Selective Electrodes Liquid Membrane Gas Sensing Probes Enzyme Electrodes. Membrane Techniques Dialysis and Reverse Osmosis Ultrafiltration Pervaporation. Solvents. 

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