Pyrolytic chromatography

A technique such as pyrolytic chromatography, which brings about the thermal decomposition of a polymer and the subsequent analysis of decomposed products by gas-phase chromatography, is useful in the latter case. It allows (a) the identification of the four benzenic derivatives formed by decomposition of the various types of triads and (b) the quantitative determination of the concentration of these compounds and their respective proportions. From such characterization it is possible to establish the molecular structure of the original copolymer. 

Solution Polymers. Acryflc solution polymers are usually characterized by their composition, solids content, viscosity, molecular weight, glass-transition temperature, and solvent. The compositions of acryflc polymers are most readily determined by physicochemical methods such as spectroscopy, pyrolytic gas—liquid chromatography, and refractive index measurements (97,158). The solids content of acryflc polymers is determined by dilution followed by solvent evaporation to constant weight. Viscosities are most conveniently determined with a Brookfield viscometer, molecular weight by intrinsic viscosity (158), and glass-transition temperature by calorimetry. 

The majority of the analytical methods for detection of N-nitroso compounds have employed gas chromatography (GC) or liquid chromatography (LC) in conjunction with a thermal energy analyzer (TEA) [20], which relies on the pyrolytic breakdown of N-NO moieties to release the nitrosyl radical. Despite the isolation techniques used, the quantitative determination of N-nitroso compounds requires a concomitant posi-... 

McMurtrey et al. [65] investigated the feasibility of determining polychlorinated biphenyls adsorbed on sediments by a procedure involving pyrolytic desorption at 1000°C, followed by gas chromatography and mass spectrometry. The procedure was capable of detecting polychlorinated biphenyl in sediment at the lOmg kgy1 level. 

Khan [181] has described a method for determining Paraquat and Diquat in soils involving catalytic dehydrogenation of the herbicide followed by gas chromatography and also a pyrolytic method [182]. 

GPC gel permeation chromatography HOPG highly oriented pyrolytic graphite... 

Typical chromatograms were observed when polystyrene was py-rolyzed in air and the pyrolytic products were analyzed by gas chromatography. A characteristic peak which was observed on the chromatograms obtained by the pyrolysis of maleic anhydride and the alternating styrene maleic anhydride copolymer but not with polystyrene was used as a reference peak. As shown in Table II, the ratio of the area under... 

The formation of block copolymers from styrene-maleic anhydride and acrylic monomers was also indicated by pyrolytic gas chromatography and infrared spectroscopy. A comparison of the pyrograms of the block copolymers in Figure 7 shows peaks comparable with those obtained when mixtures of the acrylate polymers and poly(styrene-co-maleic anhydride) were pyrolyzed. A characteristic infrared spectrum was observed for the product obtained when macroradicals were added to a solution of methyl methacrylate in benzene. The characteristic bands for methyl methacrylate (MM) are noted on this spectogram in Figure 8. 

Macroradicals obtained by the heterogeneous copolymerization of styrene and maleic anhydride in poor solvents such as benzene were used to initiate further polymerization of selected monomers. This technique was used to produce higher molecular weight alternating copolymers of styrene and maleic anhydride and block copolymers. Evidence for the block copolymers was based op molecular weight increase, solubility, differential thermal analysis, pyrolytic gas chromatography, and infrared spectroscopy. 

Polak and Molenaar described a method for the determination of acetylcholine from brain tissue by pyrolysis-gas chromatography-mass spectrometry [200]. The deuterium-labeled acetyl-choline is pyrolytically demethylated with sodium benzenethiolate, followed by quantitative GC-MS analysis. In this method, care must be taken so that the samples do not contain appreciable amounts of choline since exchange of deuterium-labeled groups between acetylcholine and choline during pyrolysis may yield erroneous results. The same authors have also reported a method for the determination of acetylcholine by slow pyrolysis combined with mass fragment analysis on a packed capillary column [201]. 

Whiting P, Goring DAI (1982) Phenolic hydroxyl analysis of lignin by pyrolytic gas chromatography Pap Puu 64 592-599... 

Parallel analyses by IR, thin-layer chromatography (TLC), and gas chromatography-mass spectrometry (GC-MS) of organic remains adhering to shards of ancient amphoras excavated in the harbor of Carthage (Tunisia) identified these remains as pine pitches. Capillary GC of methylated acid fractions showed abietic acid, dehydroabietic acid, and 7-ketodehydroabietic acid as the principal components. Two-dimensional TLC of untreated ether extracts revealed abietic acid in 12 of 31 samples and dehydroabietic acid in 26 of 31 samples. IR spectra of solid, raw samples indicated the presence of isopropyl groups, characteristic of the abietane skeleton, in 80% of the samples. Rapid and convenient analysis by TLC and IR was, in most cases, sufficient to identify pine resin products even after extensive pyrolytic and oxidative degradation. 

Pyrolytic sulfurization gas chromatography (PSGC) is a chemical analysis method by which several elements can be simultaneously determined in as little as 30-130 p.g of... 

T he expansion of the petrochemical industry and the accompanying increase in the demand for ethylene, propylene, and butadiene has resulted in renewed interest and research into the pyrolytic reactions of hydrocarbons. Much of this activity has involved paraffin pyrolysis for two reasons saturates make up most of any steam cracker feed and since the pioneering work of Rice 40 years ago, the basic features of paraffin cracking mechanisms have been known (1). The emergence of gas chromatography as a major analytical tool in the past 15 years has made it possible to confirm the basic utility of Rice s hypotheses (see, for example, Ref. 2). 

The condensation of the dilithio derivative of (R)-(+)-3-(p-tolylsulfinyl)propionic acid with protected glycoaldehy-des (O-r-butyl and 0-benzyl) gives 5-alkoxy-4-hydroxy-3-(p-tolylsulfinyl)pentanoic acids, which spontaneously cyclize to the corresponding 3-sulfinyl-4-alkoxymethyl butanolides (eq 4). Pure diastereomers can be separated by flash chromatography and are obtained in comparable amounts. The corresponding optically pure butenolides are obtained by pyrolytic elimination of the sulfoxides and then transformed into natural (-i-)-(/ )-umbelactone (eq5). 

Two new chiral carbon atoms are formed in the condensation and four diastereoisomeric p-sulfinyl y-lactones can therefore in principle be obtained. However, only two dia-stereoisomers, (3S,4, s ) and (3R,4S,Rs), are isolated when the carbanion is condensed with pivalic aldehyde, benzaldehyde, or pinacolone (yield 65-70% for aldehydes, ratio 53 47 yield 47% for pinacolone, ratio 81 19). The diastereoselectivity decreases when the two substituents of the carbonyl group are sterically similar. However, single diastereoisomers can easily be separated through chromatography and transformed in high yield into both enantiomers of optically pure saturated (by desulfurization) and a,(3-unsaturated y-lactones (by pyrolytic sulfoxide elimination) (eq 3). The relative and absolute stereochemistry of all the products have been determined by circular dichroism, nuclear Over-hauser effects, and X-ray analyses. 

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