Volume GC Injection Techniques

Liquid-Liquid Extraction for Large-Volume Injection 

The ability to inject 100 or more microliters of a liquid sample rapidly and automatically into a capillary gas chromatograph necessitates another look at liquid-liquid extraction. Sensitivity of the analysis is a common problem 

Membrane pervaporation (permselective evaporation of liquid molecules) is the term used to describe the extraction of volatile organics from an aqueous matrix to a gas phase through a semipermeable membrane. 

Steady-state permeation is governed by Fick s first law  

Membranes can be classified as porous and nonporous based on the structure or as flat sheet and hollow fiber based on the geometry. Membranes used in pervaporation and gas permeation are typically hydrophobic, nonporous silicone (polydimethylsiloxane or PDMS) membranes. Organic compounds in water dissolve into the membrane and get extracted, while the aqueous matrix passes unextracted. The use of mircoporous membrane (made of polypropylene, cellulose, or Teflon) in pervaporation has also been reported, but this membrane allows the passage of large quantities of water. Usually, water has to be removed before it enters the analytical instrument, except when it is used as a chemical ionization reagent gas in MS [50], It has been reported that permeation is faster across a composite membrane, which has a thin (e.g., 1 pm) siloxane film deposited on a layer of microporous polypropylene [61], 

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