# Chemical Analysis of Gunpowder and Gunshot Residues
## 3 Analysis of Gunpowder and Gunshot Residue
### Liquid Chromatography
However, GC is a destructive technique that can only be used to analyse volatile and semivolatile compounds, thus excluding NC and NG [14; 15; 16; 126]. Moreover, NC may decrease the GC column's lifetime [16]. In addition, thermally unstable compounds, such as nitrate esters (e.g., pentaerythnitol tetranitrate), can decompose during the analysis [15]. Furthermore, this technique cannot analyse both inorganic and organic compounds, although this can be circumvented through sampling or extraction techniques that could allow separate analysis of these compounds [15]. GC has been coupled with several detectors to analyse SG and GSR, including a flame ionisation detector (FID) [93; 103; 132], mass spectroscopy (MS) [31; 51; 93; 100; 133; 130], ion mobility spectroscopy (IMS) [100; 134], a nitrogen phosphorous detector (NPD) [26], and thermal energy analysis (TEA) [100; 103]. \begin{table}
\begin{tabular}{c c c c c} \hline
**Technique** & **Objectives** & **Target analytes** & **Matrix** & **Conclusions** & **Ref.** \\ \hline \multirow{8}{*}{SPME/GC-FID} & Estimate the time & & & Successfully detected the \\  & since discharge & & organic compounds in the \\  & and environmental & & cartridge up to 14 days \\  & effects on the & Naphthalene; & after firing; reliable \\  & estimation based & 2,6-DNT; 2,4-DNT; & Spent cartridges & determination of time \\  & on the degradation & DPA; DBP & & since discharged based on \\  & of organic & & & DPA, DBP and \\  & compounds on & & naphthalene \\ \hline \multirow{8}{*}{SPME/GC-MS} & Determination of & & & Detection of 32 OSGR in \\  & the time since & & spent cartridges; DPA and \\ \cline{1-1}  & discharge of spent & & 1,2-dicyanobenzes \\ \cline{1-1}  & cartridges & & & decrease the slowest over \\ \cline{1-1} \cline{2-5}  & Obtain chemical & & & 32 h \\ \cline{1-1}  & profiles of single & OGSR (GC) and & Unburnt & Successfully determined \\ \cline{1-1}  & GSR samples & IGSR (SEM-EDX) & gunpowder and & the chemical profile of \\ \cline{1-1}  & collected from the & & GSR & samples, using the two \\ \cline{1-1}  & shooter’s hands & & & techniques combined \\ \hline \end{tabular}
\end{table} 
Table 3: Summary of some GC techniques employed in GSR analysis. GC can also be combined with thermal desorption (TD/GC), mainly when using HSSE or SPME [29]. For example, [PERSON] et al. [132] developed an SPME/GC-FID procedure to analyse discharged cartridges and establish the time since discharge based on the degradation of organic compounds. The quantity of these analytes was also evaluated as a function of time to estimate GSR persistence upon exposure to environmental factors [132]. The results show that the authors successfully determined the time since discharge up to 14 days after firing, using several constituents of SG, namely naphthalene, 2,6-DNT, 2,4-DNT, DPA, and DBP. Environmental factors, such as sunlight exposure to discharged materials, were also studied [132]. [PERSON] et al. [102] also developed a SPME/GC-MS method with similar goals. This approach detected 32 OSGR compounds in 9 mm cartridges after discharge over 32 h. The results showed that the concentration of some compounds quickly decreased after the discharge (e.g., phenol, 2-ethyl-1-hexanol, and naphthalene), while others could still be detected 32 h after shooting (e.g., DPA and 1,2-dicyanobenzene) [102]. [PERSON] et al. [31] developed a methodology of analysing IGSR and OGSR collected from a suspect's hands. This methodology included an SPME/GC-MS analysis of OGSR compounds and an SEM-EDX analysis of IGSR particles. This combined analysis allowed the authors to obtain a complete chemical profile from the GSR samples. [PERSON] and [PERSON] [133] also combined two different rapid methodologies to characterise OGSR and IGSR detected on a suspect's hand. This approach consisted of a capillary microextraction of volatiles (CMV) followed by GC-MS and LIBS [133]. GC offers significant advantages for analysing GSR in forensic ballistics.