Vapor-phase chromatography detector

Fig. 4-6. Detector circuits for vapor-phase chromatography, (a) Thermistor detector Di, D=, Victory Eng. Corp. 32A12 thermistors Ri, Ri, 1,0000 wire wound resistors Rz, 1,0000 Helipot Rt, 10,0000 1% carbon film resistor Rs, 5,0000 1 % carbon film resistor Rt, Rj, 2,5000 1 % carbon film resistor Sw, single-pole four-position switch, (b) Hot-wire detector Rz, filament current control, to adjust filament current between 150—300 ma ( 20 ohm 5w) Ri, R4, reference detectors Rs, R, sample detectors Re, zero control 20 Re, 600 1 % carbon film resistor R, 300 1 /, carbon film resistor R, 150 1% carbon film resistor Rse, 7.5Q 1 % carbon film resistor Rs, 7.SCI 1 % carbon film resistor M, 300 ma meter,- S, single-pole six-position sv/itch.

Conventional methods of quantitation of fractions resolved by thin-layer chromatography (TLC) using techniques, such as in situ spectrophotometry or photodensitometry, are of limited utility to substances that contain weak or no chromophoric groups (1). Such fractions can be conveniently detected and quantitated by sensitive vapor phase detectors that are commonly used in gas chromatography (2,3). Several systems for quantitative TLC using vapor phase detectors have become known in recent years. 

The molecular weight and its distribution of prepolymers were determined in THF by gel permeation chromatography (Waters Associates). Four different pore size columns (10, 10, 10 and 10 A i -Styrogels) and a refractive index detector were used. The instrument was calibrated with polyisoprene samples which were prepared similarly in this laboratory and whose number-average molecular weights were determined with a vapor phase osmometer (Wescan, Model 232 A) in toluene at 50 C. 

The development of GC and the analysis of petroleum and petrochemicals have enjoyed a mutually beneficial relationship. Indeed, the first international symposium on vapor-phase (gas) chromatography was sponsored by the British Institute of Petroleum in 1956 (9). Papers describing the analysis of refinery gas, solvents, aromatics in coal-tar naphthas, and samples from the internal combustion engine were presented. Most of the work included in these presentations was done on homebuilt chromatographs. The first commercial gas chromatograph or vapor-phase fractometer was also described, along with the first ionization detector. 

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-... 

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... 

In supercritical fluid chromatography (SFC) the mobile phase is a supercritical fluid, such as carbon dioxide [15]. A supercritical fluid can be created either by heating a gas above its critical temperature or compressing a liquid above its critical pressure. Generally, an SFC system typically has chromatographic equipment similar to a HPLC, but uses GC columns. Both GC and LC detectors are used, thus allowing analysis of samples that cannot be vaporized for analysis by GC, yet cannot be detected with the usual LC detectors, to be both separated and detected using SFC. SFC is also in other... 

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