Gas chromatography pyrolysis

Pyrolysis-gas chromatography (Py—GC) is an indirect method of investigation, in which the sample is pyrolysed and the resulting volatile products are analysed by GC. By qualitative and quantitative analysis of the products formed in the pyrolysis of the sample, one can determine the structure and composition of the system under study. Unlike other chemical methods widely used with GC, pyrolysis is a complex reaction that normally proceeds in many directions and involves many stages. Nevertheless, despite these difficulties, the resulting products are adequately representative of the composition and structure of the pyrolysed samples, which is precisely what makes Py—GC a valuable method and provides for its development. 

As a rule, pyrolysis yields a complex mixture of products. This undoubtedly renders the interpretation of the results of the analysis of various substances by Py—GC more difficult. The difficulties involved, however, are not serious, and Py—GC is used extensively in analytical practice, e.g., in the analysis of polymers, in volatile organic compounds and microbiological samples. 

Analytical pyrolysis is one of the most important methods in analytical chemistry, known for many years. Thermal degradation and subsequent analysis of the degradation products have long been used for the qualitative and quantitative analysis of involatile compounds and for determining their structures [1—6]. The use of GC analysis of pyrolysis products has increased the practical value of the method because only certain of the products contained in the complex mixture formed are characteristic of a particular sample. 

The use of gas chromatography for analysing pyrolysis products is characterized by the following principal advantages  

In the early work on GC for analysis of involatile sample destruction products [7—9], pyrolysis was conducted in a special unit, the products being samples and analysed on a standard gas chromatograph. This method is recommended when small samples (about 1 — 10 mg) cannot be taken because of the inhomogeneity of the substances of interest, and for studying the mechanism and kinetics of pyrolysis, evaluating the heat resistance 

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  

Variations from 350 °C to 490 C in pyrolysis temperature produced no change in the area of the acetic acid peak, but did cause area variation in the methane peak. The pyrolysis chromatogram of poly(ethylene-ethyl acrylate) at 475 C shows one principal peak due to ethanol. No variation in peak areas was noted in the temperature range 300 °C to 480 °C. Table 3.6 shows the analysis of 0.05 g samples of poly(ethylene-ethyl acrylate (PEEA) and poly (ethylene-vinyl acrylate) (PEVA) obtained at a pyrolysis temperature of 475 °C. 

Reproduced with permission from E.M. Barrall II, R.S. Porter and J.E Johnson, Analytical Chemistry, 1963, 35, 1, 73. 1963, ACS  

Haslam and co-workers [36] employed a procedure based on pyrolysis for the determination of polyethyl esters in methacrylate copolymers. The alkoxy groups in the polymers were reacted with hydrogen iodide and pyrolysed to their corresponding alkyl iodides, which were then determined by chromatography on a dinonyl sebacate colnmn at 75 °C. Similarly, Miller and co-workers [48] determined acrylate ester imparities in polymers by converting the alkoxy groups to alkyl iodides, which were gas chromatographed on a di-2-ethyl hexyl sebacate column at 70 °C. 

Mixture Acetic add found wt% calculated Ethylene found wt% calculated Oxygen found wt% calculated 

Pyrolysis - gas chromatography - mass spectrometry has been used to identify ester groups in acrylic polymers [68]. 

Blackwell used a Curie point pyrolyser to carry out quantitative analysis of monomer units in polyhexafluoropropylene - vinylidene fluoride (Method 97). The polymer composition is calculated from the relative amounts of monomer regenerated and the trifluoromethane (CHF3) produced during pyrolysis. The exact mechanism by which trifluoromethane is produced during pyrolysis is not known but it is presumed that the free trifluoromethyl group is cleaved from the polymer backbone. The trifluoromethyl group then extracts a proton from the polymer chain to form trifluoromethane. 

Dingles, K. and Wentling, P., Angew Makromol. Chem., 5125 (1976) 

Drushell, H.V. and Iddings, F.A., Division of Polymer Chemistry 142nd meeting American Chemical Society Atlantic City, September (1962). 

Cheng Yu Wang, F., Gerhart, B.B., Smith, P.B. Analytical Chemistry, 67 3536 (1995) 

Generally speaking, the methods described in Chapters 1 and 2 for the determination of additives in polymers refer to particular known additives or, at least, to a particular class of additives such as phenolic antioxidants. Frequently, however, the analyst is faced with the problem of dealing with unknown additives in polymers, either single additives or, more commonly, mixtures of additives. He has first to identify the additive then determine it, usually in a mixture with other additives, which may interfere in the determination of the additive in which he is interested. 

Principles and Characteristics The utility of GC has prompted analysts to devise ways to introduce samples by means other than syringe to meet the needs of specific applications, including vapour-phase sample loops, heated 

The reliability of simultaneous detection of minor flash-pyrolysis products is often quite insufficient. In composite materials polymer and mineral fillers are often contained in large amounts and the con-centfation of other components is not high, typically 

Lehrle et al. [597] have reviewed the study of polymer pyrolysis by PyGC with special reference to the objective of obtaining results with quantitative significance. Since polymer decomposition is usually quite sensitive to relatively minor changes in pyrolysis conditions, quantitative analysis imposes more stringent control requirements than are necessary in the purely qualitative approach. Also Berezkin [503] has paid attention to various aspects of quantitative analysis by means of PyGC and has pointed out that it is difficult to predict the quantitative composition of the volatile decomposition products formed in pyrolysis on the basis of sample structure and pyrolysis conditions. By quantitative modelling the detailed pyrolysis mechanism 

Quantitative analytical schemes (using calibration curves, internal standardisation) have been devised for selected (copolymeric) systems [540]. An example is the determination of the composition of styrene-methacrylate by PyGC [603]. Qther applications include the quantification of rubber components [604,605], cellulose esters [606], isocyanate components of polyurethanes [607], nylon [608], plasticisers [609], aliphatic sulfur-containing additives [4]. Standardisation for quantitative analysis based on PyGC data requires careful choice of reference polymers. Use of an internal standard may improve the precision when the concentration of a single polymeric component of a blend or copolymer is calculated on the basis of PyGC data [610]. 

Pyrolysis-gas chromatography is also useful in quantitative kinetic work, where two experimental requirements are of special importance  

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Py/GC/MS. pyrolysis, gas chromatography, and mass spectrometry used as a combined technique Py/MS. pyrolysis and mass spectrometry used as a combined technique oa-TOF. orthogonally accelerated time of flight Q. quadrupole field or instrument... 

Analytical investigations may be undertaken to identify the presence of an ABS polymer, characterize the polymer, or identify nonpolymeric ingredients. Fourier transform infrared (ftir) spectroscopy is the method of choice to identify the presence of an ABS polymer and determine the acrylonitrile—butadiene—styrene ratio of the composite polymer (89,90). Confirmation of the presence of mbber domains is achieved by electron microscopy. Comparison with available physical property data serves to increase confidence in the identification or indicate the presence of unexpected stmctural features. Identification of ABS via pyrolysis gas chromatography (91) and dsc ((92) has also been reported. 

The acetyl content of cellulose acetate may be calculated by difference from the hydroxyl content, which is usually determined by carbanilation of the ester hydroxy groups in pyridine solvent with phenyl isocyanate [103-71-9J, followed by measurement of uv absorption of the combined carbanilate. Methods for determining cellulose ester hydroxyl content by near-infrared spectroscopy (111) and acid content by nmr spectroscopy (112) and pyrolysis gas chromatography (113) have been reported. 

RECENT ADVANCES IN POLYMER ANALYSIS BY MODERN PYROLYSIS-GAS CHROMATOGRAPHY/MASS SPECTROMTERY (Py-GC/MS)... 

Figure 12.8 Mia ocolumn size exclusion chromatogram of a styrene-aaylonitrile copolymer sample fractions ti ansfeired to the pyrolysis system are indicated 1-6. Conditions fused-silica column (50 cm X 250 p.m i.d.) packed with Zorbax PSM-1000 (7p.m 4f) eluent, THF flow rate, 2.0 p.L/min detector, Jasco Uvidec V at 220 nm injection size, 20 nL. Reprinted from Analytical Chemistry, 61, H. J. Cortes et al, Multidimensional chromatography using on-line microcolumn liquid chromatography and pyrolysis gas chromatography for polymer characterization , pp. 961 -965, copyright 1989, with peimission from the American Chemical Society.

For compounds of high molecular mass, however, the formation of derivatives does not help to solve the problem of in volatility. This difficulty may be overcome by breaking the large molecules up into smaller and more volatile fragments which may then be analysed by gas-liquid chromatography, i.e. by using the technique known as pyrolysis gas chromatography (PGC). 

Several experimental studies on S-MMA copolymcrization have appeared all suggest predominant combination.181" 83 Ohtani el al.m analyzed the end groups of PSMMA (60°C, AIBN, chloroform) by pyrolysis-gas chromatography to find values for the number of end groups per molecule of between 1.56-1.77 (increasing with polymer M ) which corresponds lo ail overall kjkw of between 0.39 and 0.21. Estimation of kjktc for cross termination requires knowledge of the... 

The carbon number distribution of technical secondary alkanesulfonates determined by pyrolysis gas chromatography and mass spectrometry (GC-MS) is shown in Fig. 13 together with the corresponding carbon number pattern of the raw material paraffins obtained by GC [16]. Pyrolysis was performed in a crucible-modified SGE pyrojector after covering the mixture with quartz wool. The presence of up to 10 wt % of disulfonates in technical alkanesulfonates is demonstrated by fast atom bombardment and mass spectrometry (FAB-MS) (Fig. 14) [24],... 

FIG. 13 Carbon number distribution of alkanemonosulfonates by pyrolysis gas chromatography (GC)/mass spectrometry (paraffin raw material by GC). 

Denig [118] has reported that the length and structure of the hydrocarbon chains of AOS may be determined by cleavage of the sulfo groups in presence of excess phosphorus pentoxide and hydrogenation of the hydrocarbons before determining the -alkanes and isoalkanes by pyrolysis gas chromatography. 

Pyrolysis gas chromatography is an indirect method of analysis in which heat is used to transform a sample into a series of volatile products characteristic of sample and the... 

Figure 8.45 Apparatus for pyrolysis gas chromatography. A, filament or ribbon-type pyrolyzer and B, Curie-point pyrolyzer. (Reproduced with perm.i ion from ref. 848. Copyright American Chemical society).

Mie Scattering Particle Sizing -Pyrolysis-Gas Chromatography-Ion Mobility Spectrometry (FemtoScan, ECBC)... 

PyGC Pyrolysis gas chromatography S/SL Split/splitless (capillary)... 

Smith, P B. Snyder, A. E Characterization of bacteria by quartz tube pyrolysis-gas chromatography/ion trap mass spectrometry. J. Anal. Appl. Pyrolysis 1992, 24, 23-38. 

Snyder, A. P Maswadeh, W. M. Parsons, J. A. Tripathi, A. Meuzelaar, H. L. C. Dworzanski, J. P. Kim, M. G. Field detection of Bacillus spore aerosols with standalone pyrolysis-gas chromatography-ion mobility spectrometry. Field Anal. Chem. Technol. 1999, 3, 315-326. 

G. Chiavari, N. Gandini, P. Russo, D. Fabbri, Characterisation of standard tempera painting layers containing proteinaceous binders by pyrolysis gas chromatography mass spectrometry, Chromatographia, 47, 420 426 (1998). 

Bonaduce I., Colombini M.P., Characterisation of beeswax in works of art by gas chromato graphy mass spectrometry and pyrolysis gas chromatography mass spectrometry procedures, Journal of Chromatography A, 2004, 1028, 297 306. 

T. Learner, The analysis of synthetic paints by pyrolysis gas chromatography, mass spectro metry (PyGCMS), Stud. Conserv., 46, 225 241 (2001). 

N. Gallois, J. Templier and S. Derenne, Pyrolysis gas chromatography mass spectrometry of the 20 protein amino acids in the presence of TMAH, J. Anal. Appl. Pyrol., 80, 216 230... 

M. Carbini, R. Stevanato, M. Rovea, P. Traldi and D. Favretto, Curie point pyrolysis gas chromatography/mass spectrometry in the art field. 2. The characterization of proteinaceous binders, Rapid Commun. Mass Spectrom., 10, 1240 1242 (1996). 

H. Ling, N. Maiqian, G. Chiavari and R. Mazzeo, Analytical characterization of binding medium used in ancient Chinese artworks by pyrolysis gas chromatography/mass spectrometry, Microchem. J., 85, 347 353 (2007). 

L. Osete Cortina and M.T. Domenech Carbo, Analytical characterization of diterpenoid resins present in pictorial varnishes using pyrolysis gas chromatography mass spectrometry with on line trimethylsilylation, J. Chromatogr., A, 1065, 265 278 (2005). 

K.B. Anderson and R.E. Winans, Nature and fate of natural resins in the geosphere. I. Evaluation of pyrolysis gas chromatography mass spectrometry for the analysis of natural resins and... 

L. Wang, Y. Ishida, H. Ohtani and S. Tsuge, Characterisation of natural resin shellac by reactive pyrolysis gas chromatography in the presence of organic alkali, Anal. Chem., 71, 1316 1322 (1999). 

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