A novel extraction device, capillary microextraction of volatiles (CMV) was coupled to a TRIDION-9 GC–MS with a needle trap (NTD) and evaluated for the analysis of ignitable liquids fire debris. The performance of the
TRIDION-9 was compared to a benchtop GC–MS using CMV. A system detection limit of ~10 ng for each of 20 key ignitable liquid residue (ILR) compounds was determined for the T9 GC–MS. Dynamic headspace sampling of simulated ILRs was performed in closed and open-air systems. Closed system evaluations the CMV/NTD technique resulted in extraction performance similar to the CMV alone; however, ILR analysis on the T9 was
impacted by limited chromatographic resolution. Compound identification was possible for 14 out of the 20 selected compounds on the T9 when 1 μL of a 1% standard accelerant mixture (SAM) was sampled, compared to
17 compounds on the benchtop GC–MS for the same mass loading. Open-air sampling with a modified vapor source resulted in the retention of most compounds with as low as 5 min. sampling, and equilibrium concentrations
were reached after 10 min. No significant differences were observed between CMV and CMV/NTD sampling suggesting that the combined technique does not suffer from affinity bias. While the potential of the CMV/NTD extraction coupled to a T9 GC–MS for fire debris analysis was limited by the chromatographic resolution of the instrument, this study serves as proof of concept for the CMV’s potential for the extraction of ILRs in combination with portable GC–MS systems.
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Combining Gas Chromatography-Mass Spectrometry and Principal Component Analysis to Facilitate Complete Detection and Identification of Ignitable Liquids
This paper reports an approach that developed instrumental parameters with two different GC-MS instruments. Data from the two devices were combined with principal component analysis (PCA) to analyze genuinely and ignited ignitable liquid residues (ILR). We simulate the field samples by burning seasoned pinewood soaked with each ignitable liquid (IL). Enough unburnt components from an IL remained on the burnt wood. These components were enough to reveal the chromatographic fingerprint of an IL. Most importantly, the chromatographic profile from a pure IL and IL poured onto a wooden substrate and ignited was identical. The chromatographic profiles reported from each instrument for each IL were reproducible to within 3% RSD. The MS data from both GC-MS instruments showed similar m/z peaks from all ILs, indicating similar hydrocarbon(s) and or fragmentation cluster patterns in the ILs studied ingredients. The PCA data showed characteristic differences giving rise to the separation between incendiaries, albeit some were overshadowed by clustering. In some cases, ILs that showed similar components in their mass spectra profile grouped as a class on the PCA display. We demonstrate an approach using direct headspace injection to individualize ILs recovered from crime scenes. Direct headspace injection and GC-MS combined with PCA are shown as promising facile methods for the qualitative determination of specific ILs in real-world arson samples. Initially, our project started as an undergraduate instrumental analysis guided-inquiry (GI) project. Such labs have been reported to enhance student learning and improve students' critical and problem-solving abilities. We plan to incorporate this approach in both an undergraduate instrumental analysis class and a graduate-level analytical chemistry class.
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- Award ID(s):
- 1900124
- NSF-PAR ID:
- 10328296
- Editor(s):
- Henry Charlier
- Date Published:
- Journal Name:
- The chemical educator
- Volume:
- 27
- ISSN:
- 1430-4171
- Page Range / eLocation ID:
- 33-43
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Analysis of lignin in seawater is essential to understanding the fate of terrestrial dissolved organic matter (DOM) in the ocean and its role in the carbon cycle. Lignin is typically quantified by gas or liquid chromatography, coupled with mass spectrometry (GC‐MS or LC‐MS). MS instrumentation can be relatively expensive to purchase and maintain. Here we present an improved approach for quantification of lignin phenols using LC and absorbance detection. The approach applies a modified version of parallel factor analysis (PARAFAC2) to 2ndderivative absorbance chromatograms. It is capable of isolating individual elution profiles of analytes despite co‐elution and overall improves sensitivity and specificity, compared to manual integration methods. For most lignin phenols, detection limits below 5 nmol L−1were achieved, which is comparable to MS detection. The reproducibility across all laboratory stages for our reference material showed a relative standard deviation between 1.47% and 16.84% for all 11 lignin phenols. Changing the amount of DOM in the reaction vessel for the oxidation (dissolved organic carbon between 22 and 367 mmol L−1), did not significantly affect the final lignin phenol composition. The new method was applied to seawater samples from the Kattegat and Davis Strait. The total concentration of dissolved lignin phenols measured in the two areas was between 4.3–10.1 and 2.1–3.2 nmol L−1, respectively, which is within the range found by other studies. Comparison with a different oxidation approach and detection method (GC‐MS) gave similar results and underline the potential of LC and absorbance detection for analysis of dissolved lignin with our proposed method.
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Accepted Manuscript1.0
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