Controlled-pyrolysis chromatographic

Karlen et al. analyzed acetylcholine and choline by an ion pair extraction and gas phase method [134]. The gas chromatographic estimation of the isolated acetylcholine and choline was carried out after demethylation either with benzenethiolate or by controlled pyrolysis. Acetylcholine was quantitated by flame ionization detection at the nmol level. Mass fragment analysis was employed for the determination of acetylcholine in pmol amounts. 

Barrall and co-workers [46] described a pyrolysis-gas chromatographic procedure for the analysis of polyethylene-ethyl acrylate and polyethylene-vinyl acetate copolymers and physical mixtures thereof. They used a specially constructed pyrolysis chamber as described by Porter and co-workers [47]. Less than 30 seconds is required for the sample chamber to assume block temperature. This system has the advantages of speed of sample introduction, controlled pyrolysis temperature, and complete exclusion of air from the pyrolysis chamber. The pyrolysis chromatograph of poly(ethylene-vinyl acetate) contains two principal peaks the first is methane and the second is acetic acid ... 

Carbonized Resins. A special sorbent made by controlled thermal pyrolysis of polyvinylidene chloride (Dow developmental Adsorbent XF-4175L) (34) was shown to be three to five times more effective for the collection of highly volatile compounds, such as vinyl chloride (Figure 5) and methyl chloride, than the best available activated charcoal (31,36,37). Although this sorbent is not commercially available, Carbosive and Carbosive S show similar collection properties and they are available from gas chromatographic supply houses or may be obtained already packed in small collection tubes (SKC Inc., Eighty Four, PA). 

Py-GC experiments were performed using a modified SGE pyrolysis inlet, interfaced either with a Chrompack gas chromatograph (model 437S) equipped with a flame ionization detector and a double flame photometric detector or with a Delsi gas chromatograph (model DI300) interfaced with a Delsi mass spectrometer (model R10 10). The control of the Chrompack GC and the data acquisition were done with a PCI-Chrompack program and a PC computer. 

Pyrolysis gc involves the rapid and controlled thermal decomposition of a few milligrams of the sample in the injection part of the chromatograph, the volatile products then being swept onto the column in a narrow band of earner gas. This technique is discussed more fully in section 11.5. 

The plant is controlled by a process computer (ABB-Hartmann and Braun) and equipped with numerous data-collecting instruments. Surveillance is carried out by continuous analysis of the room air as well as by explosion-limit controls. The pyrolysis gas is analyzed automatically by a gas chromatograph. All data obtained are registered to enable calculation of energy and mass balances. Some basic components are continuously monitored by infrared spectroscopy, i.e. ethylene in the pyrolysis gas, sulphur dioxide and oxygen in the exhaust gas. 

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... 

Degradative methods based on pyrolysis are the subject of renewed interest due to the identification power offered by gas chromatography-mass spectrometric systems (GC-MS) (Wershaw and Bohner, 1969 Martin et al., 1977 Meuzelaar et al., 1977 Bracewell and Robertson, 1976). There are two main pyrolysis techniques (1) controlling the decomposition kinetics by temperature programming and (2) the use of quasi-instantaneous heating (e.g.. Curie point pyrolysis). The later technique avoids most recombination reactions, but does not allow kinetic control. The pyrolysis effluent can be detected directly (Rock-Eval method) or after chromatographic fractionation. 

Two approaches to autosampling with resistively heated filaments are available, one in which multiple filaments are used and one in which a common filament is used. The former uses up to 14 different filament interfaces, each of which is connected sequentially to the gas chromatograph for pyrolysis. The computer permits individual control of each filament, so each sample may be analyzed using a different program. Like the Curie-point systems, the samples may be placed directly onto the heating filament. 

Thomas, T.H. and T.C. Kendrick, Thermal analysis of polydimethylsUoxanes. I. Thermal degradation in controlled atmospheres, J. Polym. Sci. A, 27 537 (1969). Blazsd, M., G. Garzo, and T. Szekely, Pyrolysis gas chromatographic studies on polydimethylsiloxanes and polyfdimethyl sUalkylene siloxanes), Chromatographia, 5 485 (1972). 

The phenomenon of pyrolytic scission into a large number of degradation products can be used, on the other hand, to characterize the original polymer. If the pyrolysis is carried out under standard conditions, then the degradation products of every polymer yield a characteristic fingerprint, e.g., in combination with gas chromatographic analysis. The procedure is therefore very suitable for the industrial quality control, and may also be used in clarifying polymer structure (sequence, etc.). 

Both methods require minimal if any sample preparation, and extensively automated systems are available. The highly corrosive chemicals and the harsh conditions used in the Kjeldahl digestion call for appropriate fume hoods and exhaust systems, and standardization of the digestion itself may sometimes be difficult. The relatively low sensitivity and the fairly large amount of sample required are usually no problem in the food industry. As for chromatographic methods, controlled oxidative pyrolysis of food releases a number of volatile compounds that may foul the separation columns. This requires careful maintenance of the equipment, and in particular of the precolumn that guards the separation apparatus. 

Pyrolysis gas chromatography (PGC) was one of the first combination gas chromatographic techniques, yet it is still plagued by problems of accuracy and repeatability of pyrolysis conditions and laboratory-to-laboratory reproducibility. There are three major devices for PGC (1) heated wire or ribbon, (2) tube furnace, and (3) Curie point filament. The heated wire or ribbon apparatus uses resistive heating to provide flash pyrolysis from ambient temperature to 1400°C. It can be controlled to reach the maximum temperature in milhseconds or at some fixed rate, and the device can hold the top temperature for a settable fixed time. These high-precision devices can be placed directly in the injection port (for vertical injection ports). The temperature reading should be checked from time to time to ensure accuracy. 

In this type of system a resistively heated platinum or nichrome wire coil or ribbon is used to rapidly heat the sample. The wire is continuously swept with carrier gas, whereupon the pyrolysis vapors are transported into the chromatographic column. Heating times are relatively large (up to 20 s) for this system, which may lead to nonrepeatable pyrograms and secondary reactions. The pyrolysis conditions, sample size, and location must be carefully controlled to obtain repeatable data. Two possible heating modes are available for this system pulse mode or programmed mode. For most forensic applications the pulse mode has been used. 

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