## 3 Results and Discussions
### Interferences  
Due to the trace nature of this type of profiling, it was necessary to include samples that would allow the assessment of potential contamination or interferences with the ability to successfully obtain a volatile signature. Two samples were included in the analysis which allowed an initial assessment of such a situation.  
Plastiline, an oil-based modelling clay used for mounting artefacts for microscopic analysis, was extracted and the extraction liquid was placed in a vial. Plastiline is a proprietary product whose composition is protected by patents. It generally contains oils, waxes, clay minerals, and in some cases a small portion of sulfur [34]. This is important in determining the workflow for a particular archaeological item of interest. In the situation where plastiline (or other mounting product) generates an interfering signal, the volatile signature may possibly be overwhelmed by plastiline volatiles and be unidentifiable.  
The plastiline was found to contain minimal but identifiable levels of some volatiles such as hydrocarbons, aldehydes, ethers, ketones, and aromatics. No sulfur compounds were detected in the volatile profile, indicating that the ingredients of this particular brand likely did not include any sulfur additives. Based on this initial analysis, plastiline could potentially provide an interference with volatile signatures of interest, especially when sample residues are present in trace quantities. In fact, many archaeological workflows no longer include this material due to the fact that it can cause damage to the physical appearance and chemical composition of the residues on a stone tool under examination [34].  
Figure 4: Comparison of total ion current (TIC) contour plots for three hide samples prepared by direct analysis (top); extraction in a mixture of solvents (middle); and extraction in water (bottom) on the Rtx-5 MS \(\times\) Rci-17 Sil MS column set.  
This may also be the case for the volatile signature being created by the item of interest. This type of background signal, if known to be present during the workflow of an archaeological investigation, could be subtracted from the signal of the residue being analyzed. The nature of the GC\(\times\)GC selectivity also reduces the risk that compounds of interest will co-elute with interfering compounds such as those found in plastiline. Future work may therefore require a comparison of different compositions of mounting materials, the method of application to archaeological artefacts, and the interference of these. This is less of an issue for more recent archaeological excavations, in particular those that took into account the necessary precautions for residue analysis; however, for some older excavations these potential contaminations may occur.  
Due to the fact that GC\(\times\)GC-TOFMS is a very sensitive technique, it was also necessary to determine whether the handling of archaeological artefacts without gloves may also interfere with the volatile signature from specimens of interest. The hand residue sample was produced by handling a tool with bare hands and then washing the tool with solvent to see if a background signal from the handling appeared. In this case, only trace levels of volatiles were contributed to the profile in comparison with a blank vial (Figure 1). However, it is still recommended that gloves are worn when handling specimens prior to volatile profiling. It is possible that with the sensitivity of this technique may cause the detection of secondary transfer of contaminant residues and interfere with the volatile profile of the target residue.