The system is composed of an EGA/PY-3030D micro-furnace pyrolyzer, equipped with an AS-1020E autosampler, an MJT-1035E liquid nitrogen cryo-trap system, an UV-1047Xe micro UV-irradiator, a QSP-1046E quick-stabilizing pressure flow switch (Frontier Laboratories Ltd., Japan), and a CGS-1050Ex carrier gas selector, interfaced with an 8890 gas chromatograph equipped with a 5977B bundle EI turbo mass spectrometric detector (Agilent Technologies, USA).
Analytical pyrolysis is a micro-destructive technique allowing the characterization of organic materials to be performed by thermally inducing the degradation of the sample under inert atmosphere. The sample is near-instantaneously heated at temperatures in the range 100-800 °C under inert atmosphere. In the range 100-300 °C, desorption/volatilization of the low molecular weight, volatile compounds occurs, while at higher temperatures the thermolysis of chemical bonds also occurs and a mixture of pyrolysis products, known as pyrolyzate, is formed. The pyrolysis products are then directly separated and detected by the GC/MS system. The resulting chromatographic profile – also known as pyrogram – can provide both qualitative and quantitative information on the composition of the original sample.
The technique is particularly powerful in characterizing polymers and macromolecules in general, both natural and synthetic, even in mixtures, in a wide range of molecular weight. Its main advantages are the need for a very small amount of sample (less than 100 μg) and the possibility to perform the analysis on a solid sample, without any pre-treatment. The profiles (comprising both chromatographic and mass spectrometric data) of synthetic polymers along with their additives are available in dedicated libraries, thus allowing the identification of the components of unknown mixtures to be performed automatically.
The purchased instrument constitutes the cutting edge of analytical pyrolysis technology. The pyrolysis is performed with a “drop furnace” system, in which the sample is dropped from an upper zone at room temperature to a lower zone that is pre-heated at the desired pyrolysis temperature. This technology ensures an almost instantaneous heating of the sample, and greatly improves the reproducibility of the resulting pyrograms. The furnace is directly interfaced with the injection port of the GC/MS, minimizing the risk of condensation or secondary degradation of the pyrolyzate during the transfer from the pyrolysis furnace to the chromatographic column.
Analysis set-ups
The combination of the pyrolyzer and the acquired additional instrumentation allows to operate using several instrumental setups:
Evolved gas analysis-mass spectrometry (EGA-MS)
In this technique, the pyrolysis furnace is directly coupled to the mass spectrometric detector by using a deactivated stainless steel capillary tube in place of the chromatographic column. During the EGA-MS experiment, the pyrolysis furnace is heated at a constant rate, and the evolved gas products are directly sent to the MS detector. The result of this experiment is a thermogram, that plots the ion current as a function of the temperature of the pyrolysis furnace. EGA-MS provides qualitative information on the number of components of a sample, and the temperatures at which each of them undergo desorption or pyrolysis. It is therefore an invaluable screening technique to be performed on unknown sample to establish optimal pyrolysis temperature to be used in more detailed analyses;
In this technique, the pyrolysis furnace is kept at a temperature of 300 °C or lower, allowing the desorption/volatilization of low-molecular weight compounds. The evolved compounds are then characterized by GC/MS. This technique can be used to characterize the volatile components of plastic materials, such as additives and residual monomers, without achieving the degradation of the polymeric matrix. TD-GC/MS can also easily provide information on the volatile components of natural materials. If the desorption/volatilization process of the compounds is slow, the liquid nitrogen cryo-trap system can be used to enhance the chromatographic performances;
Single-shot or flash analytical pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS)
This is the most used instrumental setup for the characterization of complex polymeric natural and synthetic materials. The sample is heated at a temperature in the range 300–800 °C, and the pyrolysis products are directly analyzed by the GC/MS system. This setup has countless possible applications, and has gathered an increasing success in many fields, including environmental chemistry, forensic analysis, industrial chemistry, and heritage science, for both routine analyses and research purposes. Interpretation of the results, which has always been regarded as the challenging step in Py-GC/MS analyses, is constantly becoming more straightforward thanks to the publication of dedicated mass spectra libraries, as well as dedicated software capable of identifying the original material from the composition of the pyrolysis mixture;
In this technique, the sample undergoes sequential instantaneous heating at more than one temperature, and the products obtained from each heating step are individually analyzed by GC/MS. This setup can be used to perform TD-GC/MS and Py-GC/MS on the same sample, analyzing the volatile components first, and then the polymeric matrix. If the polymeric matrix is composed of different species with different pyrolysis temperatures, these components can also be pyrolyzed individually performing two (or more) sequential Py-GC/MS analyses at the appropriate temperatures. As for TD-GC/MS, liquid nitrogen cryo-trapping is also possible at each step to improve the chromatographic performances;
Analytical pyrolysis-gas chromatography/mass spectrometry with online UV irradiation
The sample can undergo UV irradiation in the pyrolysis chamber, followed by direct EGA-MS (UV/EGA-MS) or Py-GC/MS (UV/Py-GC/MS) analysis to obtain information on the effects of UV light on its composition. Alternatively, the sample can be irradiated, and the volatile products generated by its photodegradation can be cryo-focused, and successively analyzed by GC/MS (UV/GC-MS). The two setups can also be combined to obtain a full characterization of the effects of UV irradiation on the sample.
Instrument equipment
The pyrolysis system is equipped with: > Micro-furnace Multi-Shot EGA/PY-3030D pyrolyser (FrontierLaboratories Ltd.) available in single-shot, double-shot, evolved gas analysis, and heart-cut (or multi-shot) pyrolysis with AS-1020E autosampler (50 sample slots); > Micro-jet liquid nitrogen cryo-trap MJT-1035E (Frontier Laboratories Ltd.), that allows the cryo-trapping and focalization of the pyrolysis products; > MicroUV-irradiator system UV-1047Xe (FrontierLaboratories Ltd.), for the on-line irradiation of samples for studying their ageing and stability, both in air and He atmosphere; QSP-1046E quick-stabilizing pressure flow switch (FrontierLaboratories Ltd.), allowing to quickly switch between air and helium when performing the online UV irradiation; > CGS-1050Ex carrier gas selector (Frontier Laboratories Ltd.), allowing to switch the carrier gas and perform the pyrolysis under different atmosphere; > Agilent 8890 gas chromatograph equipped with a mass spectrometric detector Agilent 5977B bundle EI turbo. An additional EI source (EI Extractor) is also available, which provides a further increase in the sensitivity of the system for ultra-trace analysis; > Search Database and software, including the profiles (comprising both chromatographic and mass spectrometric data) of synthetic polymers along with their additives, allowing the automated identification of the components of unknown mixtures.
By combining the results achieved in the different set-ups, it is possible to obtain complementary information on the target samples. In particular: > Evolved gas analysis (EGA) is performed by gradually heating the sample while directly connecting the pyrolysis chamber to the mass spectrometer; thus information on the thermal properties of the sample are achieved, along with the average mass spectrum of the products evolved at time intervals; > Multi-shot (or heart-cut) pyrolysis is fundamental to analyse natural and synthetic polymers in mixtures, also in the presence of additives: flash pyrolysis experiments are performed at different temperatures on the same sample, allowing the GC/MS chromatograms of the pyrolysis product released at each step to be acquired (if the pyrolysis steps are two, then the method is called “double-shot”); > UV irradiation of the single sample allows an accelerated ageing of the sample to be performed in air or He atmosphere on line, followed by the analysis of the sample by any of the described techniques (EGA, flash or multi-shot pyrolysis).
