Gas chromatography (GC) and liquid chromatography (LC) are techniques that have been indispensable to all areas of the chemical industry. Supercritical fluid chromatography (SFC) is a separation method that has features of both GC and LC. However, since SFC uses mainly carbon dioxide as the mobile phase, it has fewer applications than HPLC and GC; the compatibility between GC and LC with the use of a supercritical fluid mobile phase has therefore not been discussed. Recently, Ishii and Takeuchi reported that GC, LC, and SFC can be used in series in a single column; they named this technique "unified fluid chromatography". 1If the system could be easily made compatible with GC and LC, then in principle it could be applicable to a wide range of analyses.Our aim was to develop a double mobile-phase chromatography system with an aquatic phase as a solvent (as in LC) and a gas phase as a carrier gas (as in GC). The aquatic phase can be formed discontinuously in a capillary column by the addition of an aquatic solvent at a calculated, low flow rate. As the constructed double mobile-phase flow contains very small quantities of water, the sensitivity of the EI ionization mass detector in the GC/MS system remains constant and usual mass searches can be done by the system. We proposed that the new chromatographic method be named gas-liquid two-phase flow chromatography (2PFC). [2][3][4] A two-phase flow mobile phase is formed at the head of the capillary column by water vapor condensation, which is adjusted to the predetermined liquid to gas ratio of the two mixed mobile phases. Separation is developed by the combination of the carrier gas and condensed water as two mobile phases.2PFC is classified into hydro-membrane gas chromatography (HMGC) and alternative plug flow liquid chromatography (APFLC) by the holdup fraction (β) of the mobile phase. The void fraction (α) calculated from Eq. (1) is one of the most important parameters related to two-phase flow styles in hydrodynamics studies, which mainly discuss thermal transportation. The β value is calculated from the void fraction (α) by Eq. (2). 5where α is the void fraction, β the holdup fraction, Vg the flow rate or volume of the carrier gas, and Vw the flow rate or volume of water, HMGC is based on the annular condensation of water over the entire inner surface of the column. Formation of the hydro membrane is established in response to the planned wettability of the solid surface by water and the appropriate quantities of water vapor. The thickness of the membrane is estimated to be in the range of 4 to 20 nm by geometric calculation of the condensate, which corresponds to the sum of the water quantities of the sample solution and the moisturized carrier gas.The condensation phenomenon in a column is often identified Hydro-membrane gas chromatography (HMGC) is achieved by the annular condensation of water in a capillary column at less than 70˚C. The annular membrane of water is formed as a result of the wettability of the stationary phase, which is induced at a water ...
Alternative plugs flow liquid chromatography (APFLC), a type of gas-liquid two-phase flow chromatography (2PFC) is achieved by the agglomeration of unformed condensates in an open tubular capillary column with intermittently alternating condensates in which the supply of the liquid is maintained at a level that provides a hypothetical homogeneous film, 25 to 150 nm thick, on the inner surface. To support stable plugs, the flow mode should normally be maintained at a liquid-to-gas volume ratio (b) of between 0.0006 and 0.004 and below 70˚C. Alternative plugs flow is formed as a result of the hydrophobic property of the stationary phase, which is induced at a water contact angle above 75˚, as derived from the solubility parameter (d) of a coated resin of less than 18.3 MPa 1/2 . Diffusion and mixing between the vicinal partition fields is substantially avoided in alternating disconnected nano-volume plugs, which makes it possible to obtain a very large number of theoretical plates of separation. The plugs flow as a mobile phase can be enhanced by applying sonic vibrations to the column. Since the liquid/gas phases ratio (b) is maintained in the range of 10 -4 to 10 -3 , the extremely small volumes of solvent offer the advantages of compatibility with an EI-ionizing mass spectrometer and the use of commercially available mass search systems. The APFLC/EI-MS system, which employs commercially-available GC/MS equipment, is potentially applicable to both GC and LC analysis containing sparingly volatile components, giving close to the theoretical resolution and eliminating the need for numerous derivatization procedures.
The sorption of flavour compounds by PET and 15 copolyesters (PET copolymerized with isophthalic acid, adipic acid, sebacic acid, tetramethylene glycol, diethylene glycol, triethylene glycol and neopentyl glycol in the range of 5 to 18 mol%) was studied.Biaxially oriented films of each resin were immersed in aqueous solutions containing 37 types of flavour compounds for 4 weeks at 37 C. The amount of flavour compounds sorbed by the films was highly dependent on the copolymer composition.Among the tested films, the copolyester film containing 11 mol% sebacic acid exhibited the highest sorption of the 37 compounds, which was approximately 40 times that of PET. The copolyester film containing 11 mol% isophthalic acid exhibited the lowest sorption, approximately half that of PET. The relationship between sorption and the characteristic values of the polyester films was studied. Sorption was negatively correlated with the solubility parameter and density of the amorphous area and strongly negatively correlated with the glass transition temperature. It was concluded that the dynamic free volume involved in diffusion dominates the sorption of flavour compounds by copolyesters. The log P value and molecular size of the compounds had a strong effect on the sorption of individual flavour compounds by the films in aqueous solutions.
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