Vapor-phase chromatography retention time

Fractions were analyzed by vapor-phase chromatography (column 0.3 X 120 cm., 20% SE-52 on Chromosorb P 60/80, 130°, helium flow rate of 60 ml./min.). Retention times of 1.9 minutes for dicyclopentadiene and 4.6 minutes for the 7,7 dichlorobicyclo[3.2.0]hept-2-en-6-one were found. 

The product is analyzed by vapor phase chromatography using a 6-ft., f-in. O.D. copper tube, packed with 5% Bentone-34 (Wilkins Instrument Co.) and 0.5% XF-1150 (General Electric Silicone Products) on Diatoport-S (80-100 mesh) (F and M Co.) flow rate of helium 60 ml./min., oven temperature 85°. This column separates m-cymene (retention time 12 minutes) from />-cymene (retention time 10 minutes) but does not resolve the ortho isomer. The purity of the distilled w-cymene is above 98%. 

To a solution, at — 10 X, of butadiene (85 mg, 1.57 mmol) in the weighed amount of solvent to make 0.02 mole fraction butadiene was added solid XeF2 (50 mg, 0.295 mmol). To the stirred mixture was added BFj- OEt2 (0.2 equiv with respect to XeF2). The mixture was stirred for 10-15 min and then poured into 5 % aq NaHCO, extracted with CH2C12, and dried (MgSOJ. Methylcyclohexane was added as an internal standard, and the products were analyzed (60-75 % yields) by GC (stainless steel column. 17 ft x 0.25 in.. 5% DNP on 80/100-mesh Chromosorb W). Analysis at 35X showed 3,4-difluorobut-l-ene and trans-and d.s-1,4-difluorobut-2-ene to have retention times of 4.5, 10, and 11.5 min, respectively. Products were collected by preparative vapor-phase chromatography. 

The CH2C12 solution was analyzed by vapor phase chromatography (VPC) methods using 6 ft X % inch 30% Carbowax or 6 ft X 4 inch 20% SE-30 columns. Retention times of the reaction products were matched on both columns with precalibrated chromatographs of known... 

The conversion of the dichlorocyclobutene to cyclobutadieneiron tricarbonyl can be conveniently monitored by vapor phase chromatography. On a 5 ft. x in. column of 20% Carbowax on Chromosorb W, under conditions where the retention time of dichlorocyclobutene is 2.6 minutes, the retention time of cyclobutadieneiron tricarbonyl is 2.4 minutes. 

This chapter focuses on gas-liquid chromatography, in which compounds in a sample are separated based on vapor pressures and differences in affinity for the stationary phase (a high boiling point liquid) versus the gaseous mobile phase. The time between sample injection and detection of the individual compound eluting from the column is called the retention time. Compounds that have limited solubility in the stationary phase will exit the column quickly as a large proportion will remain in the mobile phase. Compounds with polarity similar to that of the stationary phase will have longer retention times and potentially broader peaks, due to increased interaction with the stationary phase. 

The measurement of direct interactions reveals the different strengths of molecular interactions between an analyte and the packing material surface or liquid phase. In gas chromatography, the retained compounds are vaporized and moved toward the column outlet. The analyte s volatility in the carrier gas affects the retention time. 

Using these methods is similar to reconstructing a puzzle. How the retention and vaporization mechanisms can be quantitatively analyzed, and the predicted retention times improved, based on molecular properties calculated in silica, are fundamental questions in chromatography. In gas chromatography, no solvent is used except in special cases where water vapor and ionic gas are mixed with the carrier gas. The basic retention mechanisms depend on the strength of the molecular interaction with the stationary phase, and the vaporization mechanism depends on the properties of the analytes. 

In general, boiling point and AyapH cannot be predicted. The prediction of retention time in chromatography requires the use of predictable properties. The retention time can be calculated in silica using a model phase, but vaporization has not been quantitatively analyzed. In gas chromatography, vaporization may be related to analyte volatility. The retention on methylsilicone phases was quantitatively analyzed in silica as the molecular interaction energy values. In this model system, retention time may correspond with the molecular interaction as described for retention on the methylsilicone phase. The smallest MIPS was obtained for PAHs, and the values... 

The gas-phase applications of polymeric resins are primarily used for gas chromatography and purification of air by removal of contaminants. The work of Hollis (1966) laid the foundation for the use of resins as packing materials for GC analysis. Hollis reported relative retention times of over 50 gas molecules on different EVB/styrene/DVB resins, using beads packed in a column. The same beaded forms are used today. The water vapor isotherm on the styrene/DVB resin... 

Chromatography separates a mixture into its components, which are then analyzed by one of many detectors. In GC, the sample is passed during the vapor phase through an appropriated solid bed placed in a column. An oven supplies heat to the column, through which the vapor is carried using a constant stream of a gas such as nitrogen or helium. The time required to elute each component retention time) is monitored. (Analysis times can run for more than an hour.) GC refers to die use of solid absorbent or molecular sieve columns. In the majority of GC... 

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