Pyrolysis Gas Chromatography Py-GC

Before discussing the applications of this technique to microstructural studies of polymers, one must understand the principles of the technique, and the factors which 

A small quantity of the polymer is mounted on an inert metal support and an electrical current is passed through the support (filament method) or external heat is supplied to the support (furnace method) so as to rapidly heat up and break down (i.e., pyrolyse) the polymer into a mixture of smaller molecules which, under standard pyrolysis conditions, are characteristic of the polymer being examined. Products are swept from the pyrolysis chamber by a stream of carrier gas onto a gas chromatographic column and separated into their individual components before passing through the detector, which records their retention time (time taken, under standard conditions, to travel from pyrolysis chamber to detector) and quantity (peak height under standard conditions). 

This is the essence of the Py-GC technique. It is possible to then pass the separated pyrolysis products one at a time into a mass spectrometer to obtain definitive information regarding their precise identity, i.e., pyrolysis-mass spectrometry. 

---

The FTIR spectra of the gas mixture evolved in thermal decomposition of Bisphenol AF poly(formal) (7) at various temperatures suggest the existence of benzene rings, C—O—C bonds, and C=C bonds. In a pyrogram of pyrolysis gas chromatography (Py-GC) of Bisphenol A (3), a-methylstyrene, phenol, p-cresol, 4-hydroxy-amethylstyrene, and isopropyl phenol are observed as major peak products. The cleavage reactions shown in Scheme (5) is suggested for the formation of phenol and 4-hydroxy-a-methylstyrene from Bisphenol A (3). 

Pyrolysis-gas chromatography (Py-GC) A pyrolysis technique in which the volatile pyrolysates are separated and detected by gas chromatography. 

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. 

The chemical characterization of forensic evidence from a crime scene or the criminal has some different requirements from that of many other types of chemical analysis. High sensitivity is important because the quantity of material for examination is often limited to minute traces found at the scene. The material under scrutiny must be characterized as comprehensively as possible to ensure maximum discrimination from other material in the same class. Forensic laboratories are multiinstrument facilities required to deal with many types of evidence found at a crime scene therefore, the routine methods used should preferably employ relatively inexpensive instrumentation. In order to protect integrity, samples should be analyzed as received if possible and any workup minimized. The method should preferably not be labor intensive. Pyrolysis-gas chromatography (Py-GC) and pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) have proven to be an effective means of satisfying these requirements in many forensic science laboratories. - ... 

Pyrolysis-gas chromatography (Py-GC) has been widely applied to the characterization of various synthetic polymers. However, it is often difQcult to characterize intractable condensation polymers such as aromatic polyesters by ordinary Py-GC, even using a high-resolution capillary GC system, because they usually degrade into a number of polar compounds along with considerable amounts of solid residues and chars. 

Radhakrishnan and Rao [1] have studied the kinetics and mechanism of the degradation of thiol terminated polysulfide polymers HS(RSS) RSH, R-CH -CH OCH -OCH -CH - which have been cured with ammonium dichromate using pyrolysis-gas chromatography (Py-GC) and isothermal and dynamic thermogravimetric analysis (TGA). 

Pyrolysis-gas chromatography (Py-GC) Thermal decomposition is one of the oldest methods for studying the composition of polymers, and is a valuable tool in the industrial analysis of plastics. The analytical use of Py-GC is based on the fact that the polymer structure determines its reactivity and thus also the qualitative and quantitative composition of the pyrolysis products. The technique combines the advantages of a highly efficient separation method with a directly connected pyrolysis unit, so that the degradation products can be analyzed immediately after their formation. Curie-point pyrolyzers yield the most reproducible results due to short temperature... 

Coupled chromatographic techniques Several chromatography techniques (C) have been used for sulfur determination. These techniques allow generally very sensitive detection of sulfur-containing compounds (see Table 1). Usually, sulfur is first oxidized followed by ion chromatography. Typically, such analyses require sophisticated chemical procedures but this is not always the case for example, the technique using pyrolysis-gas chromatography (Py-GC) equipped with a flame photometric detector (FPD) does not require sample pretreatment. 

Adipate and phthalate type Mild pyrolysis - gas chromatography (Py-GC) [27]... 

Two thermal methods have been extensively studied in recent years, pyrolysis-gas chromatography (Py-GC) - mass spectrometry (MS) and evolved gas analysis involving infrared spectroscopy (IR) - MS, thermogravimetry and differential scanning calorimetry (DSC). 

Separation methods such as thin layer chromatography (TLC) and pyrolysis-gas chromatography (Py-GC) are useful for comparison of questioned and known specimens when there is sufficient material and the destruction of the specimens is not an issue. In order to identify poljuners and certain additives, numerous trace evidence examiners have established libraries of known Py-GC. Commercial... 

Wampler and Levy [1] have discussed factors affecting reproducibility in pyrolysis - gas chromatography (Py-GC) such as sample size, sample inhomogeneity, and pyrolyser design. There are two broad areas of application of Py-GC. The first is its use as a means of qualitatively identifying unknown polymers, for example, competitors products or in forensic investigations. This fingerprinting approach, useful as it is, is not pursued further in this book. 

Pyrolysis-gas chromatography (Py-GC) of LDPE gives details of its microstructure, and is a versatile tool to show the extent of degradation. Two LDPE were investigated one was LDPE with a masterbatch consisting of LDPE, corn starch (7.7%), and prooxidant (SBS-1 manganese stearate) (LDPE-MB) the other was 30 pm films of pure LDPE with pro-oxidant (LDPE-PO). 

---