William A. MacCrehan

Detection of Smokeless Powder Residue on Pipe Bombs by Micellar Electrokinetic Capillary Electrophoresis

Improvised explosive devices are an increasing concern among law enforcement agencies within the United States because of their destructive capability. Capillary electrophoresis has been used previously for the forensic analysis of inorganic constituents in explosives. Micellar electrokinetic capillary electrophoresis (MECE), also known as micellar electrokinetic chromatography (MEKC), is well suited for the forensic analysis of organic constituents of these materials because of its high sensitivity and small sample requirements. In the present study, pipe bombs filled with known types of smokeless gun powder were detonated under controlled conditions. Samples of explosive residue were collected from the post-blast fragments and analyzed using MECE. The results were compared to the known types and analyzed to investigate the feasibility of matching post-blast residue to a specific powder used as explosive charge.

Liposome Behavior in Capillary Electrophoresis

The behavior of liposomes in capillary electrophoresis is studied for the purpose of developing a potential method for characterizing liposomes prepared for use in industrial and analytical applications. This study characterizes the electrophoretic behavior of liposomes under various conditions to provide information about electrophoretic mobility and liposome-capillary surface interactions. The results of this method are compared with the results obtained using traditional laser light-scattering methods to obtain size information about liposome preparations. Additionally, reactions of liposomes and the surfactant n-octyl-β-d-glucopyranoside are performed off-line in bulk solution experiments and on-line in the capillary. Automated delivery of lysis agents by multiple electrokinetic injections is demonstrated as a general method for inducing on-capillary reactions between liposomes and other reagents. Furthermore, some preliminary evidence on the use of liposomes as a hydrophobic partitioning medium for analytical separations is presented.

Electrochemical Detection in Liquid Chromatography: Application to Organometallic Speciation

Abstract The development of a new technique for the measurement of organometallic species is presented. It combines the resolution of high performance liquid chromatography with sensitive electrochemical detection used in a reductive mode. Past difficulties with this detection system have been overcome including the choice of a suitable working electrode and purification of the solvent. The redox behavior of the organometals in the chromatographic solvent was studied by cyclic voltammetry in order to optimize the detector cell potential. A separation of organomercurials and a multielement organometal mixture demonstrate the applicability of the system. Linear calibration curves can be obtained over a wide concentration range the detection limit for trimethyllead cation is about 0.1 ng.

Comparing the additive composition of smokeless gunpowder and its handgun-fired residues.

Detecting the use of handguns via the determination of the organic additives in smokeless gunpowder residues (OGSR) presents a promising alternative to primer metal residue analysis. Compositional analysis of the gunpowder additives nitroglycerin, diphenylamine, and ethyl centralite provides information that can associate residue samples with unfired gunpowder. We evaluated the composition of seven reloading smokeless gunpowders, both in bulk and as single particles, by ultrasonic solvent extraction/capillary electrophoresis. Handgun-fired residues obtained from three common weapon calibers loaded with the known reloading powders were compared with the unfired powders. In general, the composition of the residues was similar to that found in the unfired powders. For double-base powders, comparing the ratio of the propellant (P) to the total amount of stabilizer (S) for both residue and gunpowder samples proved to be a useful measurement for identification. This P/S ratio demonstrated that the additives in the residues did not greatly change relative to the unfired powder, providing a useful indicator to aid in forensic powder and residue evaluation.

Reversed-phase high-performance liquid chromatographic separation and electrochemical detection of retinol and its isomers

Baseline separation of the isomers of retinol using reversed-phase high-performance liquid chromatography (HPLC) in less than 30 min is presented. A new approach to the detection of retinol using electrochemical detection is developed. The oxidative electrochemistry of retinol is studied at a glassy-carbon electrode using coulometry, ultraviolet-visible spectrophotometry and HPLC. Amperometric detection in HPLC for retinol provided a linear response from 0 to 1.5 micrograms/ml and a detection limit of 4.1 ng/ml. Electrochemical detection was compared to ultraviolet-visible absorbance detection for the determination of retinol in human serum extracts. Good agreement is found for the results obtained with the two detectors.

A NIST standard reference material (SRM) to support the detection of trace explosives.

SRM 2905 Trace Particulate Explosives was developed to simulate the residues produced by handling plastic and military explosives. A series of nine candidate materials were prepared by coating chromatographic supports with either Composition C-4 (containing RDX (hexahydro-1,3,5-trinitro-1,3,5-Triazine) and HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-Tetrazocine)) or TNT (2,4,6-trinitrotoluene). Criteria for selection of the best material for the SRM included: coating efficiency, extractability with organic solvents, thermal storage stability, consistency of the particle size with fingerprint residues, and suitability for calibration of trace explosives detectors. The final base material selected for the SRM was octadecylsilane-modified silica (C(18)) with a nominal 20-30 microm particle size. Four materials comprise the SRM, with two nominal concentrations of explosive, 0.01% and 0.1% (mass fraction) for both C-4 and TNT, respectively. The final certified concentrations were determined by liquid chromatography (LC) with ultraviolet absorbance detection (LC/UV) and a liquid chromatography with mass spectrometric (LC/MS) method using negative ion atmospheric pressure ionization (APCI(-)) with an acetate ionization additive that improves quantitation. The SRM was tested on a table-top field explosives detector based ion mobility spectrometry (IMS).

Role of biogenic thiols in the solubility of sulfide minerals

Abstract Efforts to account for observed trace metal concentrations in anoxic marine waters have had only limited success due in part to the lack of knowledge of the identity and concentration of the organic sulfur compounds that are present. There have been no previous attempts to measure trace metals concentrations simultaneously with the inorganic and organic sulfur species in marine waters. In addition to the conventional methods for the determination of the inorganic species, we are developing methods for the determination of the biogenic thiols and disulfides using an HPLC separation coupled to selective electrochemical detection. Preliminary results on the analysis from anoxic sediment pore waters will be presented. Current thermodynamic models describing the solubility of sulfide minerals in anoxic marine waters will be refined to include complexation of chalcophile trace metals by organic thiols.

Investigating the effect of changing ammunition on the composition of organic additives in gunshot residue (OGSR).

The measurement of the organic additives in smokeless gunpowder is an attractive approach for the detection of handgun use because it provides compositional information that can help associate residues and unfired gunpowder. We investigate several factors that will be required to advance the characterization of organic gunshot residue (OGSR) as a useful forensic tool, including evaluating residue contamination from previously fired ammunition, particle-to-particle compositional variability, and compositional features resulting from the type of firing primer used. Using ammunition loaded with known smokeless powders containing different stabilizers, a sequence of shots was fired from a .357 magnum revolver, and the muzzle exit residues were collected. Compositional analysis of the residues, both in bulk and as single particles, showed only a trace of the previously fired powder in the first shot and none in subsequent shots. In an additional experiment testing conventional leaded and the new lead-free firing primers, the OGSR composition was found not to depend on the primer type.

Sampling Protocols for the Detection of Smokeless Powder Residues Using Capillary Electrophoresis

Present techniques for the detection of gunshot residue rely primarily metallic primer components such as lead, barium and antimony. With the advent of reformulated primers that reduce or eliminate these elements, new methods for the detection of organic residue compounds will be needed. Micellar electrokinetic capillary electrophoresis (MECE) is one technique that has been successfully applied to the analysis of these smokeless powder residue compounds. Protocols for the recovery of the organic residue components under a variety of sampling conditions were evaluated and improved for MECE analysis. The collection of residue samples where external contaminants such as grease or blood were present on the residue substrate were investigated using both tape lifts and solvent swab protocols. In addition, residue component recovery using supercritical fluid extraction techniques was preliminarily evaluated for samples contaminated with blood.

Hair combing to collect organic gunshot residues (OGSR)

A protocol is presented for the collection and analysis of gunshot residues (GSR) from hair. A fine-toothed comb is used for collection of the residues. A small zip-closure bag serves as a container for both sample storage and extraction of the characteristic organic powder additives. The success of this residue recovery approach was tested on simulated shooters and victims using mannequin-supported human wig hair as well as on human shooters. Residues were collected from four weapons: a revolver and semi-automatic pistol, rifle and shotgun. One characteristic additive, nitroglycerin, was detected by capillary electrophoresis (CE) in the majority of the collection experiments.