Organic FDR detection

Devise a method to enable organic FDR detection to be readily incorporated into our existing systems for inorganic FDR and organic explosive residue detection. 

On the basis of this work there is poor correlation between the detection of inorganic and organic FDR in casework, and organic detection appears to be more sensitive than the detection of inorganics. However, one of the cases examined (FI) was atypical and consisted of 100 exhibits consequently there are insufficient data to draw firm conclusions about the value of organic FDR detection. 

Organic FDR detection is a useful additional technique, despite the fact that single-based propellant constituents cannot be reliably detected. The current system uses GC/TEA as a rapid screening technique for NG and 2,4-DNT, and only positive samples need to be subjected to the SPE cleanup/ concentration procedure. The method is flexible in that the extract can be analyzed by a range of analytical instrumentation. There does not appear to be good correlation between the detection of organic and inorganic FDR which emphasizes the need for combined instrumentation, that is, GC/TEA, GC/MS, and SEM/EDX. Details of the method devised are as follows. 

Although there is extensive literature on the identification and detection of propellants, little work has been devoted to the combined analysis of organic and inorganic FDR recovered from hands and clothing in forensic casework. The analysis of organic FDR has concentrated on the detection of NG and 2,4-DNT by HPLC/PMDE. The HPLC/PMDE system requires a... 

For a trial period of 3 months, clothing submitted to the laboratory for inorganic FDR analysis was also examined for organic FDR. Organic residues detected during the trial period were not used as evidence in criminal proceedings. In all 13 different firearm-related incidents (cases FI through F13) a total of 186 exhibits were examined. One case FI accounted for 100 exhibits. The positive results are listed in Table 26.7. 

Only one exhibit, mask (a) in case F13, was positive for inorganic FDR, although no organic FDR was detected on this item. The indicative inorganic particles lead, barium were detected in 17 exhibits from four cases but, in the absence of any unique inorganic particles, they were reported as negative. 

Despite all the considerable improvements, the particle analysis method remains a lengthy and costly procedure. These disadvantages have renewed interest in the possibility of detecting the organic components of FDR, either as a primary method or as a screening technique. 

Chromatographic techniques are the main methods that have been used to separate, detect, and identify organic components of FDR.152 162 Other methods considered include molecular luminescence,163 infrared spectroscopy,164 Raman spectroscopy,165 electron spin response spectrometry,166 microchemical crystal tests,167 168 ultraviolet spectroscopy/nuclear magnetic resonance/polarography.169... 

Many of the organic constituents of FDR are explosive or explosive-related compounds and much of the work already done on the detection of explosive residues can be extended to include FDR. Explosives and their residues are usually analyzed using chromatographic techniques. Chromatography is the general name given to the methods by which two or more compounds in a mixture physically separate by distributing themselves between two phases (a) a stationary phase, which can be a solid or a liquid supported on a solid, and (b) a mobile phase, either a gas or a liquid which flows continuously around the stationary phase. The separation of individual components results primarily from differences in their affinity for the stationary phase. 

The detection and identification of the organic constituents in FDR has the potential to be used either as a screening technique or, much more likely, as a complementary technique to the particle analysis method. The particle analysis method has proved very satisfactory and has been well tried and tested in casework and court. The objective is to devise an efficient system for organic firearm residue detection that is entirely compatible with the particle analysis method. As a suspect may need to be examined for both firearm and explosive residue the method must also be compatible with organic explosive residue detection techniques. 

It would be desirable to examine environmental and occupational particles containing one or more of the elements strontium, titanium, and zinc and to compare them with discharge particles, in order to establish whether or not it is possible to differentiate the FDR particles. If not, the particle analysis method may still be a useful tool to provide supporting evidence, particularly if organic propellant constituents are also detected on the suspect. 

The ability to detect organic constituents in FDR from ammunition with single-based propellant was the ultimate goal. If this proved impossible, the investigation would at least clarify the situation and improve the detection method for NG, which could serve as a useful complementary technique to SEM/EDX. If particles in the indicative category were accompanied by NG, it would substantially raise the significance level of such particles. 

The suction sampling and analysis techniques were repeated to determine if organic and inorganic FDR could be detected on clothing worn during the firing of one round of ammunition from a revolver. The results are listed in Table 26.6. 

Detectable quantities of organic and inorganic residues were recovered from the laboratory coats. The amounts of NG, DPA, and EC detected were well above the detection limits of the systems. A smaller number of inorganic FDR particles were recovered from the laboratory coats compared to the garments doped with six shots. 

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