The method uses desorption electrospray ionization (DESI)-tandem mass spectrometry and directly desorbs and detects analytes from surfaces without any sampling process. Typical transitions for MC and EC, m/z 241 to m/z 134 and m/z 269 to m/z 148, respectively, were used to improve the assay sensitivity. The testing found that MC and EC can be detected on various surfaces, with detection limits of 5-70 pg/square cm. Interferences, detection time after shooting, and the number of times hands were washed after shooting were also assessed. None of the materials interfered with the results, and the detection window for organic GSRs was up to 12 hours. Hands could be washed at least six times. Additional samples were analyzed in order to confirm the reliability of this method. The method successfully distinguished shooters from nonshooters. The method is useful for forensic analysis of GSRs because of its simplicity, high throughput, and the direct detection of MC and EC on suspects’ hands, clothes, and hair. This method supplies more characteristics information than other methods of GSR detection, such as chemical visualization and SEM/EDX method. The description of the experiment addresses the chemicals used; DESI source and mass spectrometry; ammunition, shooting, and sampling; and safety considerations. 3 figures, 2 tables, and 26 references