# Chemical Analysis of Gunpowder and Gunshot Residues
## 4 Summary  
Recent legislative proposals in several countries indicate a change in the paradigm that will lead to the removal of heavier metals from ammunition. These changes eliminate the inorganic compound mixture characteristic of GSR and may force researchers to shift the focus of their analysis to OGSR compounds. Therefore, methods more suitable for analysing OGSR compounds, such as chromatography and spectroscopy, are being developed.  
Several studies have reported the successful use of alternative methods to detect, identify, and quantify OGSR compounds. Nonetheless, some researchers point to better efficiency when combining both OGSR compounds and IGSR particles analysis. For this reason, combination of the standard analysis method of IGSR particles (SEM-EDX) with chromatographic or spectroscopy analysis of OGSR compounds could be a suitable avenue for future research for forensic laboratories dealing with GSR analysis. The combination of two techniques with different target analytes--or a single technique with the capability of analysing both organic and inorganic GSR, such as Raman or FTIR spectroscopy [50; 74; 116; 120; 121]--could help to accomplish this goal. The results of the combined analysis of organic and inorganic residues could be used, in the best scenario, to correlate a sample with reference material, aiding in the investigation of a crime in which firearms were used.  
Up to now, no standard analytical methodology for OGSR compounds has been implemented. SPME followed by GC-MS is one of the most promising methodologies for achieving standardisation, as it has consistently yielded superior results according to numerous authors [102; 107; 109; 132]. In addition, a standardized method for data analysis must also be defined. Chemometrics showed that it can be a suitable method of studying the data and creating databases. This information can potentially be used with several statistical procedures [135; 140; 141; 142; 143; 54; 144; 145; 146; 147; 148] to compare and identify samples based on those databases.  
These alternative analytical methods can be extremely helpful in forensic ballistics, particularly for firearm-related elements found in crime scenes in which the conventional forensic ballistic visual comparison cannot be used. In addition, these methods produce a considerable number of data points that have driven, and currently are driving, the exploration of new approaches to answer other vital questions within this field. These include the development of predictive models to determine time since shooting and firing distances and to identify ammunition's manufacturer and its model. These methods can take advantage of the most recent statistical and machine learning tools currently available for model development and of modern computational database systems for efficient storage and data access.  
Conceptualisation, M.S., S.M.A. and C.F.; writing--original draft preparation, M.S.; writing--review and editing, S.M.A., A.Q. and C.F.; supervision, S.M.A. and C.F.; project administration, A.Q.; funding acquisition, A.Q. All authors have read and agreed to the published version of the manuscript.  
The authors would like to thank FCT--Foundation for Science and Technology, I.P. for financial support under the project UIDB/04585/2020.  
Data Availability Statement: Data sharing not applicable.  
The authors declare no conflict of interest.  
Not applicable.