Thermal chromatograph

The MP-3 Thermal Chromatograph (Spex Industries, Inc., Me-tuchen, NJ) facilitates the slow (up to 40°C/min) controlled atmosphere pyrolysis of solid oil shale. The volatile compounds produced are monitored by both flame ionization and thermal conductivity detectors and after trapping, the whole or portions of the evolved organic proflle may be further subjected to GC and other analytical procedures. In contrast, the CDS 100 pyroprobe and associated CDS 820 reaction system (Chemi-... 

The thermal chromatograph is the instrument of choice for the heating of small (mg) shale samples. These are heated under controlled conditions of temperature increase under a chosen atmosphere, and volatiles produced are carried directly through thermal conductivity and/or fiame ionization detectors. After trapping of all or part of the evolved species, GC may be carried out. A typical pyrolysis profile of the total volatiles produced with respect to temperature for both types of detection is shown in Figure 11. The characteristic twin-humped curve is seen with thermal conductivity detection. The latter hump, which is absent... 

Another subtractive pre-column which shows potential utility is molecular sieve 5A. This material is known to selectively subtract straight chain organic species, although compounds other than alkanes are removed. Table II shows results obtained at different final pyrolysis temperatures for oil shale samples pyrolyzed in the thermal chromatograph. 

Figure 4. - Schematic of Pyran Thermal Chromatograph System...

Thermal Chromatography. The effect of heating rate on oil yields, composition and rate of formation was carried out with a commercial thermal chromatograph (Model MP-3 Chromalytics, Inc.). This instrument contains the following elements l) a temperature programmable pyrolyzer, 2) an evolved gas analyzer with both flame ionization (F.I.D) and thermal conductivity (T.C.) detectors,... 

Caffeine is extracted from beverages by a solid-phase microextraction using an uncoated fused silica fiber. The fiber is suspended in the sample for 5 min and the sample stirred to assist the mass transfer of analyte to the fiber. Immediately after removing the fiber from the sample it is transferred to the gas chromatograph s injection port where the analyte is thermally desorbed. Quantitation is accomplished by using a C3 caffeine solution as an internal standard. 

An ion beam can be produced from a number of different sources, but for this instmment — used for biochemical examination of thermally unstable, large molecules — an atmospheric-pressure inlet such as APCl or ES would generally be used. These can be operated with liquid inlets from chromatographic columns or simply from static solutions. 

Gyclodextrins. As indicated previously, the native cyclodextrins, which are thermally stable, have been used extensively in Hquid chromatographic chiral separations, but their utihty in gc appHcations was hampered because their highly crystallinity and insolubiUty in most organic solvents made them difficult to formulate into a gc stationary phase. However, some functionali2ed cyclodextrins form viscous oils suitable for gc stationary-phase coatings and have been used either neat or diluted in a polysiloxane polymer as chiral stationary phases for gc (119). Some of the derivati2ed cyclodextrins which have been adapted to gc phases are 3-0-acetyl-2,6-di-0-pentyl, 3-0-butyryl-2,6-di-0-pentyl,... 

Acrolein is produced according to the specifications in Table 3. Acetaldehyde and acetone are the principal carbonyl impurities in freshly distilled acrolein. Acrolein dimer accumulates at 0.50% in 30 days at 25°C. Analysis by two gas chromatographic methods with thermal conductivity detectors can determine all significant impurities in acrolein. The analysis with Porapak Q, 175—300 p.m (50—80 mesh), programmed from 60 to 250°C at 10°C/min, does not separate acetone, propionaldehyde, and propylene oxide from acrolein. These separations are made with 20% Tergitol E-35 on 250—350 p.m (45—60 mesh) Chromosorb W, kept at 40°C until acrolein elutes and then programmed rapidly to 190°C to elute the remaining components. 

The routine compositional and functional testing done on the adhesives includes gas chromatographic testing for purity, potentiometric titrations for acid stabilizer concentrations, accelerated thermal stabiUty tests for shelf life, fixture time cure speed tests, and assorted ASTM tests for tensile shear strengths, peel and impact strengths, and hot strengths. 

A review pubHshed ia 1984 (79) discusses some of the methods employed for the determination of phenytoia ia biological fluids, including thermal methods, spectrophotometry, luminescence techniques, polarography, immunoassay, and chromatographic methods. More recent and sophisticated approaches iaclude positive and negative ion mass spectrometry (80), combiaed gas chromatography—mass spectrometry (81), and ftir immunoassay (82). 

Gc/ftir has both industrial and environmental appHcations. The flavor and aroma components in fragrances, flavorings, and foodstuffs can be identified and quantified via gc/ftir (see Food additives). Volatile contaminants in air, water, and soil can be analy2ed. Those in air are usually trapped in a sorption tube then injected into the chromatograph. Those in water or soil are sparged, extracted, or thermally desorbed, then trapped and injected (63,64). 

Many physical principles can be employed by different sensor vendors to obtain the same measurement. For example, in 1995, 49 vendors were listed for hydrogen sensing (2). Represented among the sensor systems are mass spectrometers, gas chromatographs, electrochemical cells, thermal... 

SPME has been utilized for deterrnination of pollutants in aqueous solution by the adsorption of analyte onto stationary-phase coated fused-siUca fibers, followed by thermal desorption in the injection system of a capillary gas chromatograph (34). EuU automation can be achieved using an autosampler. Eiber coated with 7- and 100-p.m film thickness and a nitrogen—phosphoms flame thermionic detector were used to evaluate the adsorption and desorption of four j -triazines. The gc peaks resulting from desorption of fibers were shown to be comparable to those obtained using manual injection. 

More specific methods involve chromatographic separation of the retinoids and carotenoids followed by an appropriate detection method. This subject has been reviewed (57). Typically, hplc techniques are used and are coupled with detection by uv. For the retinoids, fluorescent detection is possible and picogram quantities of retinol in plasma have been measured (58—62). These techniques are particularly powerful for the separation of isomers. Owing to the thermal lability of these compounds, gc methods have also been used but to a lesser extent. Recently, the utiUty of cool-on-column injection methods for these materials has been demonstrated (63). 

So far the plate theory has been used to examine first-order effects in chromatography. However, it can also be used in a number of other interesting ways to investigate second-order effects in both the chromatographic system itself and in ancillary apparatus such as the detector. The plate theory will now be used to examine the temperature effects that result from solute distribution between two phases. This theoretical treatment not only provides information on the thermal effects that occur in a column per se, but also gives further examples of the use of the plate theory to examine dynamic distribution systems and the different ways that it can be employed. 

Sotolon (4,5-dimethyl-3-hydroxy-2(5H)-furanone) and solerone (4-acetyl- y-butirrolactone) were claimed to be responsible for some aroma characteristic of flor sherries wines. These compounds are present only as traces, and are chemically unstable. A system of two gas chromatographs coupled with a four-port switching valve was used to quantitate these components without previous fractionation. The first chromatograph was equipped with an on-column injector, in order to avoid thermal degradation of sotolon in the heated injector, a DB-5 column and an FID. The second chromatograph was equipped with an on-column injector, a DB-1701 column and an FID. The method allowed quantification of solerone and sotolon at concentrations as low as a few ppb (29). 

Nevertheless, a number of gas chromatographic applications exist, epecially those for the determination of crude oil indicators. Such indicators are used as geochemical parameters for the thermal history of the crude as well as to indicate the possible relationship between crudes from different wells. These indicators comprise a number of isomeric aromatic species, such as the individual alkylnaphthalenes (44, 45), the individual Cio-mono-aromatics or the individual C9-mono-aromatics. The ratio between these isomers gives a definite indication of the crude oil. In general, these systems use a Deans switching unit to make a heart-cut, which then is focused, reinjected and separated on a second column with a different polarity. 

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