A new high photoluminescent metal–organic complex is proposed as an optical marker for the indentification of
gunshot residues (GSR) produced from firearms. The marker containing Eu3+ ion was synthesized producing the
[Eu(PIC)3(NMK)3] complex, where PIC is picric acid and NMK is n-methyl caprolactam. It was chemically characterized
using emission spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric and differential
thermal analyses, and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESIFT-ICR
MS) and then added to conventional ammunition as function of its concentration (from 2 to 50 mg by ammunition).
Marked conventional GSR was visually and chemically detected by UV irradiation (λ = 395 nm) and
ESI-FT-ICR MS. The tests indicated that marked GSR is easily visible in proportions above of 25 mg on the target,
bullets and firearms regions and on the arm of shooter. It was also detected at lower concentrations using ESI-FTICR
MS. A final cost of the process is evaluated be lower than US$ 1.50/by ammunition, where 1 g of marker
suffices to tag approximately 40 .40 bullets.