Determination of Al(III), Pb(II), and Cu(II) in Gunshot Residue Using Amino-Functionalized Silica Adsorbents in Dispersive Solid Phase Microextraction (DSPME) with Capillary Electrophoresis (CE)

Here is reported the design, synthesis, and application of an amino silica adsorbent for the extraction and determination of Al(III), Pb(II), and Cu(II) in gunshot residue (GSR) from the dorsal and palmar zones by capillary electrophoresis. The extraction procedure was used to determine the adsorbent composition by varying the molar ratio of the cross-linking agent tetramethyl orthosilicate (TMOS) and the functional monomer 3-aminopropyl trimethoxysilane (APTMS). (5.0:0.0 to 0.0:5.0). The optimal composition (3.0:2.0) was characterized using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and adsorption isotherm analysis. A univariate method was used to optimize critical factors in dispersive solid phase microextraction (DSPME), including the adsorbent mass, contact time, sample volume, and elution solution. Using the optimal conditions (adsorbent, 10 mg; contact time, 10 min; sample volume, 5 mL; eluent solution, methanol/10(-1) mol L-1 HNO3), the method provides limits of detection of 0.06 mg L-1 for Pb(II), 0.08 mg L-1 for Cu(II), and 0.11 mg L-1 for Al(III). The precision and accuracy were evaluated in terms of inter- and intra-day repeatability (n = 3) with a relative standard deviation below 10%. The developed method was applied for gunshot residue analysis, providing concentrations from 12.6 to 702 mg L-1 for Al(III), 11.8 to 280 mg L-1 for Pb(II), and 29.8 to 395.6 mg L-1 for Cu(II).