Desorption Electrospray Tandem MS (DESI‐MSMS) Analysis of Methyl Centralite and Ethyl Centralite as Gunshot Residues on Skin and Other Surfaces

Abstract

A direct and sensitive method for the detection of methyl centralite (MC) and ethyl centralite (EC) as gunshot residues (GSRs) has been developed. This 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. It has been shown that MC and EC can be detected on various surfaces, with detection limits of 5-70 pg/cm(2). Interferences, detection time after shooting and the number of times hands were washed after shooting were also evaluated. None of the materials interfered with the results and the detection window for organic GSRs was up to 12 h and hands could be washed at least six times. Further samples were analyzed to confirm the reliability of this method, and showed that it could discriminate shooters from nonshooters. This method should be of significance in forensic science, especially in analyzing GSRs, because of its simplicity, high throughput, and the direct detection of MC and EC on suspects' hands, clothes, and hair.

Recent trends in organic gunshot residue analysis

“…The evidential value of this technique would significantly increase with the inclusion of several additional OGSR compounds. The authors stated, however, that the capability for this is present, based on previous studies that used DESI-MS for the detection of for example diphenylamine (DPA) and its nitration products from propellant powders [68,69].…”

“…The major advantages associated with desorption electrospray ionisation (DESI) are its capability of direct analysis of solid surfaces without the need for sample preparation and the compatibility with portable mass spectrometers [68]. These advantages, in conjunction with the real time analysis capability of DESI-MS, its simplicity and the high throughput, give rise to a potential screening application of this technique.…”

“…These advantages, in conjunction with the real time analysis capability of DESI-MS, its simplicity and the high throughput, give rise to a potential screening application of this technique. Furthermore, the potential of DESI-MS to supply structural information in real time [68] could enable the combined function as a screening and confirmatory technique, possibly even in a single run.…”

“…Zhao et al [68] used DESI-MS/MS successfully for the detection of subnanogram levels of OGSR compounds, based on the presence of methyl centralite (MC) and ethyl centralite (EC), from several solid surfaces including a human hand. They reported no interference from the tested surfaces and were able to detect OGSR for up to 12 hours and hands could be washed at least six times.…”

Preliminary classification of characteristic organic gunshot residue compounds

“…Nitro-208 glycerin and nitrocellulose are both used in pharmaceutical prepara-209 tions [26,27]. Nitrocellulose also occurs in lacquers, varnishes and 210 celluloid films [26,27] and in printing [26].…”