Vapor-phase chromatography VOLUME

Henry s Law constant for the equilibrium is KH = (Vc/Vg)((t/to) — 1). Vc and Vg are the volumes of condensed and vapor phases in the column (i.e. for gas-liquid chromatography, Vc is the volume of the liquid film on the supported packing or open tubular wall, and Vg the volume of void space, respectively). If the column is in the linear range (small loading) the resolution is,... 

The bulk phase diagrams of pure hydrocarbons and mixtures are well known from the experiments. In the work by Sage et al. [3], the bubble point pressures of methane + n-butane mixtures are determined experimentally from the discontinuity of isothermal compressibility of constant-composition mixture at the point of phase transition. The composition of vapor phase is determined in that work from the residual specific volume of gas. Later experiments employ phase recirculation techniques [4] to achieve vapor-Uquid equilibrium [5, 6], and the phase compositions are analyzed by more advanced methods such as gas chromatography. 

Inverse gas chromatography can be used to obtain the polymer-solvent interaction parameter in the limit of 2 = 1. Here x is found from the retention volume of the low molecular-weight component in the vapor phase as it is eluted over the polymer which is the stationary component in a gas-phase chromatography experiment. 

The method is based on the determination and the analysis of an amount of trapped vapor phase, which has been stripped from the liquid phase by a known volume of inert gas. The carrier gas has to pass several saturators filled with the same liquid mixture of known composition, in order to be saturated with vapors. Then, the collected amount of condensate corresponds directly to the partial pressure(s). The typical experimental setup (applicable to systems of electrolytes, too) is described by Linek and Hala (67LIN1). Other stills can be found elsewhere, e.g. (910VE1) or (75ANA1). A semimicromethod based on gas chromatography was presented by (63WIC1)... 

Liquid water and liquid benzene have very small mutual solubilities. Equilibria in the binary water-benzene system were investigated by Tucker, Lane, and Christian as follows. A known amount of distilled water was admitted to an evacuated, thermostatted vessel. Part of the water vaporized to form a vapor phase. Small, precisely measured volumes of liquid benzene were then added incrementally from the sample loop of a hquid-chromatography valve. The benzene distributed itself between the hquid and gaseous phases in the vessel. After each addition, the pressure was read with a precision pressure gauge. From the known amounts of water and benzene and the total pressure, the liquid composition and the partial pressure of the benzene were calculated. The fugacity of the benzene in the vapor phase was calculated from its partial pressure and the second viiial coefficient. 

The headspace analysis procedure is simple the food is sealed in a container, then brought to the desired temperature and left for a while to establish an equilibrium between volatiles bound to the food matrix and those present in the vapor phase. A given volume of the headspace is withdrawn with a gas syringe and then injected into a gas chromatograph equipped with a suitable separation column (static headspace analysis). Since the water content and an excessively large volume of the sample substantially reduce the separation efficiency of gas chromatography, only the major volatile compounds are indicated by the detector. The static headspace analysis makes an important contribution when the positions of the aroma sub-... 

E. C. Goosens, D. de Jong, G. J. de Jong and U. A. Th Brinkman, Reversed-phase liquid cliromatography coupled on-line with capillary gas chromatography. II. Use of a solvent vapor exit to ina ease introduction volumes and introduction rates into the gas cliromato-graplT, J. Microcolumn Sep 6 207-215 (1994). 

Liquid chromatography creates a huge volume of gas when solvent vaporizes at the interface between the column and the mass spectrometer.22 Most of this gas must be removed prior to ion separation. Nonvolatile mobile-phase additives (such as phosphate buffer), which are commonly used in chromatography, need to be avoided when using mass spectrometry. Pneumatically assisted electrospray and atmospheric pressure chemical ionization are dominant methods for introducing eluate from liquid chromatography into a mass spectrometer. 

A second way to resolve quench problems is to separate the sterols from the pigments by thin layer chromatography (TLC). Briefly, samples are concentrated by evaporation and redissolved in a small volume (<100 xl) of chloroform or hexane and spotted onto a pre-dried, silica gel G, TLC plate along with 5 xg of cholesterol standard. Components are resolved with a mobile phase comprised of petroleum ether, diethyl ether, and acetic acid at a 300 200 1 ratio. Sterols migrate 1/4 to 1/3 of the way to the top of the plate, while pigments stay at or near the origin. Spots are visualized with iodine vapor, marked with a pencil, scraped into scintillation... 

Gas chromatography (GC) is based on the distribution (partition) of a volatile solute between a mobile gas phase and a stationary liquid (GLC) or solid (GSC). The solute is introduced at the column inlet as a plug of vapor and is swept throu the column by the carrier gas. Depending on the partition coefficients, differing volumes of carrier gas are required to elute the solutes from the column. Owing to the dynamics of the experiment, the results are u ally expressed in GC as retention volumes rather than partition coefficients. For convenience, solute retention data are given either at column temperature or at 0 °C, with... 

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