Environmental Analysis using Pyrolysis-Gas Chromatography/ Mass Spectrometry

Transcription

1 Honours Research Proposal 2010 Environmental Analysis using Pyrolysis-Gas Chromatography/ Mass Spectrometry Name: Sheridan Barter ( ) Supervisors: Dr. Claire Lenehan (Flinders University), Paul Pigou (Forensic Science South Australia) Pyrolysis is a method by which samples of very low volatility are broken down into smaller, more volatile components using thermal degradation [1]. This allows for the analysis by gas chromatography/mass spectrometry; a powerful analytical technique for the separation and analysis of a sample. This analysis would otherwise require more extensive extraction methods in order to introduce these types of samples as a gas. Pyrolysis Gas Chromatography/Mass Spectrometry (Py-GC/MS) is a common tool in forensic and analytical chemistry and is often employed in cases for the analysis of polymers, drugs, adhesives, paints, inks, photocopy and printer toners, rubber tyre marks, etc [1-6]. Pyrolysis is achieved using one of three different types of pyrolyzers; microfurnace, curiepoint and resistively heated. Curie-point pyrolysis is highly reproducible due to the rapid heating and the control over the temperature. The induction coil raises the temperature until the curie-point of the ferromagnetic wire is reached, and remains constant until the wire is switched off. This is the temperature at which the wire loses its magnetism, dependent on the wire alloy [1]. A range of different wires are available allowing for the selection of an appropriate temperature [2]. Forensic Science South Australia has a Py-GC/MS containing a curie-point pyrolyzer, and it is this instrument that will be used throughout the project. In order to run a typical sample, a small portion is placed on the end of the ferromagnetic wire into the pyrolyzer, which is interfaced with the GC column via an injector port, and heated using a high frequency induction coil (refer to Fig1). The pyrolyzates are flushed into the column by helium gas where they are separated on the chromatographic column based on their relative polarities and detected using mass spectrometry.

2 Figure 1: Schematic diagram of a curie-point Py-GC [7] This project aims to investigate the discriminative ability of Py-GC/MS in the analysis of environmental samples including plant resins and soil samples. This is often important in forensic cases in order to identify the likely source of origin, or species of origin allowing the connection or exclusion of crime scene samples with a place of interest. Plant resins are non-volatile, non-water soluble excretions produced by a plant in response to infection or incision [8]. Preliminary research into the differentiating abilities of Py-GC/MS for plant resins was conducted by Blee in a previous honours research project [9]. During this project Blee showed that acacia gum resin and ironwood gum resin produced very similar spectra using Fourier Transform Infrared (FTIR) spectroscopy. This resulted in difficulties in using FTIR for the discrimination of these resins. Further work by Blee showed that these samples were visually different using thermogravimetric analysis and Py-GC/MS. This project seeks to extend the work of Blee by analysing a number of different resins collected from trees across Australia from a number of species, the majority from the eucalyptus genus. This study aims to differentiate between samples and to determine whether or not an unknown sample can be positively identified from comparison of its Py-GC/MS spectra. Furthermore, we seek to assess the potential of Py-GC/MS for the discrimination of soil samples. Py-GC/MS is a well-known analytical technique for the analysis of soils [10]. Many components in soils have been successfully identified using this method, but the

3 discriminatory power of the analysis is yet to be studied. Currently, there is a multitude different methods by which soil samples are compared, from simple colour analysis and microscopy to X-ray diffraction analysis (XRD) [11] scanning electron microscopy - energy dispersive X-ray spectrometry (SEM-EDX) [12], particle size analysis, Fourier Transform Infrared spectrometry and UV-Vis spectroscopy [13], or a combination of a number of these techniques. Many of these techniques have the ability to differentiate between samples, but the sample preparation, sample size, and analysis time can be extensive in comparison to the information obtained. Py-GC/MS is therefore advantageous over these methods due to the small sample size required, minimal sample preparation and analysis time, and the ability of mass spectrometry to positively identify multiple soil constituents, whereas these other techniques cannot. The instrument used for this project will be a Fischer GSG Curie Point Pyrolyser 1040PSC with a PerkinElmer Clarus 500 gas chromatograph and PerkinElmer quadrupole mass spectrometer, located at Forensic Science South Australia. In order to ensure a homogenous sample that is representative of the whole, both the soil and plant resin samples will be crushed. Previous soil analysis methods often describe extensive extraction techniques before the analysis [14-16], but some have simply ground and sieved their samples [17]. The crushing procedure would be the preferable technique, but the feasibility of these methods will be tested to ensure reproducibility. In order to calculate the true ability of Py-GC/MS to distinguish between these samples, multivariate chemometric analysis of the spectra obtained will be performed with the aid of software such as Minitab 15, or similar. This will involve the use of hierarchical clustering and principal component analysis [18]. The proposed timeline for the year has been outlined in figure 2.

4 Figure 2: proposed timeline for 2010 Complete coursework Collect samples Learn how to operate Py-GC/MS Analyse Samples Analyse spectra using chemometrics Write up report

5 REFERENCES 1. Sobeih, KL, Baron, M & Gonzalez-Rodriguez, J 2008, Recent trends and developments in pyrolysis-gas chromatography, Journal of Chromatography A, vol. 1186, pp Ahmad, Z, Al-Sagheer, F & Al-Awadi, NA 2010, Pyro-GC/MS and thermal degradation studies in polystyrene-poly(vinyl chloride) blends, Journal of Analytical and Applied Pyrolysis, vol. 87, pp Sato, M, Hida, M & Nagase, H 2004, Analysis of pyrolysis products of methamphetamine, Journal of Analytical Toxicology, vol. 28, pp Cook, CE & Brine, DR 1985, Pyrolysis products of heroin, Journal of Forensic Sciences, vol. 30, no. 1, pp Aziz, N, Greenwood, PF, Grice, K, Watling, RJ & van Bronswijk, W 2008, Chemical fingerprinting of adhesive tapes by GCMS detection of petroleum hydrocarbon products, Journal of Forensic Sciences, vol. 53, no. 5, pp Egan, WJ, Galipo, RC, Kochanowski, BK, Morgan, SL, Bartick, EG, Miller, ML, Ward, DC & Mothershead, RF 2003, Forensic discrimination of photocopy and printer toners. III. Multivariate statistics applied to scanning electron microscopy and pyrolysis gas chromatography/mass spectrometry, Analytical and Bioanalytical Chemistry, vol. 376, pp PerkinElmer seminar files, Pyrolysis Instrumentation received via from Ken Swain, agent for PerkinElmer in South Australia, March 22, Dell, B & McComb, AJ 1979, Plant Resins Their Formation, Secretion and Possible Functions, Advances in Botanical Research, vol. 6, pp Blee, A 2008, Unravelling Secrets from the Past: A Chemical Investigation honours thesis, Flinders University, Adelaide 10. Tsuge, S 1995, Analytical pyrolysis past, present and future, Journal of Analytical and Applied Pyrolysis, vol. 32, pp Petraco, N, Kubic, TA & Petraco, NDK 2008, Case studies in forensic soil examinations, Forensic Science International, vol. 178, pp Cengiz, S, Karaca, AC, Çakir, I, Üner, HB & Sevindik, A 2004, SEM-EDS analysis and discrimination of forensic soil Forensic Science International, vol. 41, pp Thanasoulias, NC, Piliouris, ET, Kotti, MSE & Evmiridis, NP 2002, Application of multivariate chemometrics in forensic soil discrimination based on the UV-Vis spectrum of the acid fraction of humus, Forensic Science International, vol. 130, pp Saiz-Jimenez, C & deleeuw, JW 1984, Pyrolysis-gas chromatography- mass spectrometry of soil polysaccharides, soil fulvic acids and polymaleic acid, Organic Geochemistry, vol. 6, pp

6 15. Nierop, KGJ, van Bargen, PF, Buurman, P & van Lagen, B 2005, NaOH and Na 4 P 2 O 7 extractable organic matter in two allophonic volcanic ash soils of the Azores Islands a pyrolysis GC/MS study, Geoderma, vol. 127, pp Vancampenhout, K, Wouters, K, De Vos, B, Buurman, P, Swennen, R & Deckers, J 2009, Differences in chemical composition of soil organic matter in natural ecosystems from different climatic regions A pyrolysis-gc/ms study, Soil Biology & Biochemistry, vol. 41, pp Nierop, KGJ, Pulleman, MM & Marinissen, JCY 2001, Management induced organic matter differentiation in grassland and arable soil: a study using pyrolysis techniques, Soil Biology and Biochemistry, vol. 33, pp Miller, JN & Miller JC, Statistics and Chemometrics for Analytical Chemistry, 5 th edn.; Pearsons Education Limited: England, 2005