Hyphenated Thermal Methods

While TGA provides useful data when a mass change is involved in a reaction, we have seen that many reactions do not have a change in mass associated with them. The use of both TGA and DTA or TGA and DSC provides much more information about a sample than either technique alone provides. There are several commercial thermal analysis instrument manufacturers who offer simultaneous combination systems, often called simultaneous thermal analysis (STA) systems. Simultaneous TGA-DTA and simultaneous TGA-DSC instruments are available. Instrument combinations cover a wide temperature range and come in both analytical sample size (1-20 mg) 

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The thermal characterisation of elastomers has recently been reviewed by Sircar [28] from which it appears that DSC followed by TG/DTG are the most popular thermal analysis techniques for elastomer applications. The TG/differential thermal gravimetry (DTG) method remains the method of choice for compositional analysis of uncured and cured elastomer compounds. Sircar s comprehensive review [28] was based on single thermal methods (TG, DSC, differential thermal analysis (DTA), thermomechanical analysis (TMA), DMA) and excluded combined (TG-DSC, TG-DTA) and simultaneous (TG-fourier transform infrared (TG-FTIR), TG-mass spectroscopy (TG-MS)) techniques. In this chapter the emphasis is on those multiple and hyphenated thermogravimetric analysis techniques which have had an impact on the characterisation of elastomers. The review is based mainly on Chemical Abstracts records corresponding to the keywords elastomers, thermogravimetry, differential scanning calorimetry, differential thermal analysis, infrared and mass spectrometry over the period 1979-1999. Table 1.1 contains the references to the various combined techniques. 

The so-called hyphenated techniques , incorporating thermal methods as one of the combined analytical techniques are sure to play an increasing role in the identification and characterization of crystalline forms of pharmaceutical substances. The combination of TGA with FTIR allows the simultaneous quantitative analysis of weight changes during thermal processes with the IR identification of the decomposition products (e.g. solvent) resulting from those processes (Materazzi 1997). For substances with low volatility, the FTIR analysis may be replaced with mass spectroscopy (Materazzi 1998). 

Apart from combined TA techniques (on-line or not) the actual trends in thermal analysis are the introduction of modulated and high-resolution techniques, hyphenated thermal analysis methods e.g. TG-FTIR, TG-MS, DSC-XRD, etc.), alternative heating modes, microthermal analysis methods, industrial standardisation and quality control. Modulation means a periodic perturbation of a temperature program. Temperature modulation finds application in DSC, TG, DETA, TMA and uTA. Temperature-modulated techniques, such as Modulated DSC (MDSC ) and Modulated TGA (MTGATM), broaden the insight into the material properties. The use of modulated temperature programs in thermal methods has been reviewed [37,37a]. 

As an alternative to wet ehemical routes of analysis, this monograph deals mainly with the direct deformulation of solid polymer/additive compounds. In Chapter 1 in-polymer spectroscopic analysis of additives by means of UV/VIS, FTIR, near-IR, Raman, fluorescence spectroseopy, high-resolution solid-state NMR, ESR, Mossbauer and dielectrie resonance spectroscopy is considered with a wide coverage of experimental data. Chapter 2 deals mainly with thermal extraction (as opposed to solvent extraction) of additives and volatiles from polymerie material by means of (hyphenated) thermal analysis, pyrolysis and thermal desorption techniques. Use and applieations of various laser-based techniques (ablation, spectroscopy, desorption/ionisation and pyrolysis) to polymer/additive analysis are described in Chapter 3 and are critically evaluated. Chapter 4 gives particular emphasis to the determination of additives on polymeric surfaces. The classical methods of... 

Reports on the detailed thermal behaviour of PEEK/HAp composites [as well as other polymer/HAp (nano)composites] are scarce in the literature. Advanced thermal analysis methods, e.g., modulated temperature differential scanning calorimetry (MTDSC) or hyphenated thermoanalytical methods such as thermogravimetry coupled with Fourier transform infrared spectroscopy (TG-FTIR) or mass spectrometry... 

This book covers some of the significant advances in hyphenated techniques in polymer characterization with a focus on thermsd-spectroscopic techniques and other methods. This book is organized into two sections. The first section focuses on general considerations concerning hyphenated characterization techniques. The second section focuses on coupled thermal techniques and coupled-thermal-spectroscopic techniques. We hope that this book will encourage and catalyze additional activity in hyphenated characterization method development and the application to polymer characterization. 

T. Provder, M. W. Urban, and H. G. Barth, eds.. Hyphenated Techniques in Polymer Characterisation Thermal-Spectroscopic and Other Methods, American Chemical Society, Washington, D.C., 1994. 

Various ancillary GC techniques are headspace GC (Section 4.2.2), thermal desorption GC, pyrolysis GC, hyphenated methods (Chapter 7), multidimensional techniques (Section 7.4.1) and process GC. 

This chapter deals mainly with (multi)hyphenated techniques comprising wet sample preparation steps (e.g. SFE, SPE) and/or separation techniques (GC, SFC, HPLC, SEC, TLC, CE). Other hyphenated techniques involve thermal-spectroscopic and gas or heat extraction methods (TG, TD, HS, Py, LD, etc.). Also, spectroscopic couplings (e.g. LIBS-LIF) are of interest. Hyphenation of UV spectroscopy and mass spectrometry forms the family of laser mass-spectrometric (LAMS) methods, such as REMPI-ToFMS and MALDI-ToFMS. In REMPI-ToFMS the connecting element between UV spectroscopy and mass spectrometry is laser-induced REMPI ionisation. An intermediate state of the molecule of interest is selectively excited by absorption of a laser photon (the wavelength of a tuneable laser is set in resonance with the transition). The excited molecules are subsequently ionised by absorption of an additional laser photon. Therefore the ionisation selectivity is introduced by the resonance absorption of the first photon, i.e. by UV spectroscopy. However, conventional UV spectra of polyatomic molecules exhibit relatively broad and continuous spectral features, allowing only a medium selectivity. Supersonic jet cooling of the sample molecules (to 5-50 K) reduces the line width of their... 

Hyphenated methods can be divided into two types those that do and those that do not destroy the sample in the process of analysis. Spectrophotometric methods, thermal conductivity, and refractive index methods of detection do not destroy the sample. Chromatographic methods using flame ionization and similar detection methods destroy the sample as it is detected. Any hyphenated method that involves MS or thermal analysis (TA) will also destroy the sample. In most cases, the identification of the components in soil is most important, so the destruction of the analyte is of less importance. 

There are four basic hyphenated methods that result in the sample being destroyed. These are GC-MS, HPLC-MS, AAS/ICP-MS and TA/DTA-MS. All mass spectroscopic methods destroy the sample after separation however, both AAS and ICP destroy the sample no matter what follow-on method of analysis is used. In most cases, TA and differential thermal analysis (DTA) will also destroy the sample. The follow-on methods then analyze the components that result from this decomposition. DTA may also be used to follow transitions in the sample without destroying it. Because the sample is identified, there is typically no reason to collect the analyte of interest, and so destruction is not of concern. However, if there is a limited amount of sample, care should be taken in using one of these methods. 

Spectroscopy has become a powerful tool for the determination of polymer structures. The major part of the book is devoted to techniques that are the most frequently used for analysis of rubbery materials, i.e., various methods of nuclear magnetic resonance (NMR) and optical spectroscopy. One chapter is devoted to (multi) hyphenated thermograviometric analysis (TGA) techniques, i.e., TGA combined with Fourier transform infrared spectroscopy (FT-IR), mass spectroscopy, gas chromatography, differential scanning calorimetry and differential thermal analysis. There are already many excellent textbooks on the basic principles of these methods. Therefore, the main objective of the present book is to discuss a wide range of applications of the spectroscopic techniques for the analysis of rubbery materials. The contents of this book are of interest to chemists, physicists, material scientists and technologists who seek a better understanding of rubbery materials. 

Anthony, G. M. Kinetic and chemical studies of polymer cross-linking using thermal gravimetry and hyphenated methods. Degradation of polyvinylchloride. Polymer Degradation and Stability 1999 64 353. 

Thermal analysis involves observation of the usually very delicate response of a sample to controlled heat stimuli. The elements of thermal-analysis techniques have been known since 1887 when Le Chatelier used an elementary form of differential thermal analysis to study clays (4), but wide application did not come until the introduction of convenient instrumentation by du Pont, Perkin-Elmer, Mettler and other sources in the 1960 s. Currently, instrumentation and procedures are commercially available for DTA, DSC, TGA, TMA, and a number of so-called hyphenated methods. Several methods are currently under study by ASTM committees for consideration as to their suitability for adoption as ASTM standards. 

Figure 2.9 Overview of sample introduction methods and hyphenated techniques used in ICP-AES. (A) Pneumatic concentric (sometimes called the Meinhard nebuliser) (B) Babington (C) fritted disc (D) Hildebrand nebuliser (E) cross flow (G) standard ultrasonic nebuliser for aqueous and non-aqueous solvents (H) electro-thermal graphite ( ) electro-thermal carbon cup (K) graphite tip filament (L) laser ablation (M) hydride generation (P) flow injection...

MS has more analytical flexibility than FTIR, but interfacing a thermal analyzer is more difficult because of the low operating pressure required for MS. MS instruments typically operate at approximately 10" torr, while thermal analyzers are usually at atmospheric pressure. One approach is to evacuate the thermal analyzer, but the common method used is a differential pumping system such as that used for GC-MS. This reduces the pressure from the thermal analyzer in several stages prior to allowing the gas flow into the mass analyzer. A commercial interface for a thermal analyzer-MS system, shown in Figure 16.31, uses a supersonic jet to skim analyte molecules into the MS, in a manner similar to the jet separators used in GC-MS. Jet separator operation is discussed in the chapter on GC (Chapter 12) under hyphenated techniques. 

This entry examines several recent advances in pyrolysis gas chromatography-mass spectrometry (Py-GC/MS). The use of anal3dical pyrolysis coupled to GC/MS in polymer studies has greatly increased in the past few years because of the hyphenation between a technique permitting a fast thermal program to yield volatile fragments with a powerful tool for their identification. The classical application of Py C/MS to thermoplastics has been extended recently to thermosets and even to hiopolymers and biocomposites. The use of these techniques to study alternative methods for waste treatment has also been considered as an important and recent feature, showing possibilities for further improvement in the amount of its applications. A brief overview on the identification of polymer additives by Py-GC/MS has also been carried out. 

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