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.

A novel method for determination of diphenylamine (DPA) and its nitrated derivatives, which are considered as characteristic components in smokeless powder and gunshot residues, is described. A tandem mass spectrometric method is established and mass spectrometer parameters optimized for each compound to obtain higher sensitivity. Under optimum conditions, quantitative analysis was carried out. The linear ranges are 5.0-200.0, 2.0-200.0 and 5.0-250.0 ng ml-1 and the detection limits are 1.0, 0.5 and 2.5 ng ml-1 for diphenylamine (DPA), N-NO-diphenylamine (N-NO-DPA) and 4-NO2-diphenylamine (4-NO2-DPA), respectively. Intra-assay and inter-assay precision and accuracy of analysis of these three samples were investigated. Based on the regression lines obtained above, smokeless samples were analyzed. It was found that there are 0.952% DPA, 0.384% N-NO-DPA and 0.128% 4-NO2-DPA in smokeless powder. Recovery tests showed that using cotton swabs, 80.3 +/- 4.9% DPA, 79.6 +/- 3.1% N-NO-DPA and 83.1 +/- 5.4% 4-NO2-DPA could be recovered from human hands.

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This paper describes a novel method to detect gunshot residues (GSRs). The components contained in the double-based smokeless powder were separated by using a HPLC system with UV detection at 223 nm. The result indicated that there are mainly two kinds of organic ingredients in the double-base smokeless powder used. These two organics do not include nitrocellulose because it has no evidential value in the HPLC-UV trace of the smokeless powder sample. By matching retention times of these two compounds with that of the five standards occurring in smokeless powder, the compounds are tentatively identified as methyl centralite (MC) and nitroglycerin (NG). These two compounds were finally identified by using MS spectrum. This MS-MS method was developed to detect MC since MC is less commonly found in the environment than NG. In Chinese ammunition, MC is widely used as a stabilizer instead of EC. Sixteen samples were used to evaluate the reliability of the method. The mean (±SD) MC level in the eight samples is 520.1 ± 271.9 pg/µL and that in the blanks is 31.0 ± 20.8 pg/µL. The result (P = 0.0007) shows that there is a significant difference between the two serial data. Sampling hands over a 24 h period showed that GSR could be detected even after 8 h with a 75% decrease in the level of MC. The result of the washing test shows that it is still possible to apply the proposed method to detect GSRs on a shooter's hands even if their hands have been washed three times. Another test shows that if the shooters wear gloves while firing, MC on the gloves can be easily detected using the proposed method.

This study aimed to investigate the effect of water content on the properties and structure of oleogels by developing walnut oleogel based on potato starch and candelilla wax (CW).