Developing a quantitative extraction technique for determining the organic additives in smokeless handgun powder.

Compositional analysis of the organic additives in smokeless handgun powder can provide forensic information to associate known and questioned samples. A reliable method for the quantitative extraction of smokeless powder additives would strengthen these measurements. To achieve quantitative recovery, both supercritical fluid extraction (SFE) and ultrasonic solvent extraction (USE) were evaluated as candidate techniques. Following a detailed evaluation of the solvent choice, the recovery of spiked additive compounds, and the effect of the powder matrix, a reliable USE technique was developed. When quantitative USE recovery of the target analytes, nitroglycerin (NG), diphenylamine (DPA), and ethyl centralite (EC), is coupled with additive measurement by micellar capillary electrophoresis (CE), compositional information can be obtained in less than 1 h.

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.

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.

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.

Fabrication of plastic microfluid channels by imprinting methods.

Microfluidic devices have been fabricated on poly(methyl methacrylate) substrates by two independent imprinting techniques. First-generation devices were fabricated using a small-diameter wire to create an impression in plastics softened by low-temperature heating. The resulting devices are limited to only simple linear channel designs but are readily produced at low cost. Second-generation devices with more complex microchannel arrangements were fabricated by imprinting the plastic substrates using an inverse three-dimensional image of the device micromachined on a silicon wafer. This micromachined template may be used repeatedly to generate devices reproducibly. Fluorescent analtyes were used to demonstrate reproducible electrophoretic injections. An immunoassay was also performed in an imprinted device as a demonstration of future applications.

NIST/NCI Micronutrients Measurement Quality Assurance Program: measurement repeatabilities and reproducibilities for fat-soluble vitamin-related compounds in human sera.

The NIST/NCI Micronutrient Measurement Quality Assurance Program has conducted 33 interlaboratory comparison exercises for fat-soluble vitamin-related compounds in human sera over the past 12 years. Periodic reanalysis of lyophilized serum samples prepared from more than 70 different sera has enabled estimation of the short- and long-term measurement characteristics. Median- and interquartile-range-based statistics adequately estimate the distribution of results from laboratories that are in analytical control from total distributions that include a significant minority of outlier data. Short-term interlaboratory reproducibility standard deviations (SDs) are predictable functions of analyte concentration, with an asymptotic limit at low analyte concentration and a linear relationship at high concentrations. Long-term trends in the interlaboratory reproducibility can be estimated by standardizing the short-term SD at the observed analyte concentration to an expected SD at a given physiologically significant analyte concentration. The "average" laboratory's same-day analytical repeatability SD is about one-third of the estimated interlaboratory reproducibility; repeatability for longer periods between analyses is, on average, on better than the reproducibility. While a few exceptional laboratories have maintained excellent repeatability over the entire decade, long-term study measurements generated within a single laboratory are not generally more internally consistent than results from multiple laboratories. Enhanced and more consistently implemented intralaboratory quality control and quality assurance methods are required to further improve and maintain interlaboratory measurement comparability.

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-ß-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.

Determination of vitamin K1 in serum using catalytic-reduction liquid chromatography with fluorescence detection.

A new method for the liquid chromatographic-fluorescence determination of serum vitamin K1 is described using reduction of the K-quinone to the fluorescent K-hydroquinone. The reduction reaction occurs "on-line" in the LC system using a catalytic reducer column and an alcohol mobile phase as reductant. A procedure for serum determination utilizes a liquid-liquid serum lipid extraction followed by normal-phase fractionation on a solid-phase extraction cartridge. The final measurement uses a reversed-phase (C18) separation with a ethanol-methanol mobile phase and provides a detection limit of approximately 20 pg/ml.

Determination of retinol, alpha-tocopherol, and beta-carotene in serum by liquid chromatography with absorbance and electrochemical detection.

We describe a method for the determination of retinol, alpha-tocopherol, and beta-carotene in serum, using a liquid-chromatographic separation with wavelength-programmed ultraviolet/visible absorbance and amperometric electrochemical detection with a glassy carbon electrode. After protein denaturation and addition of an internal standard, tocol, 250-microL samples are twice extracted with hexane. The reversed-phase, gradient-elution chromatographic separation provides baseline resolution of: the all-trans isomer of retinol from the cis isomers, alpha- from gamma-tocopherol, and all-trans-beta-carotene from alpha-carotene and from cis-beta-carotene isomers. The linearity of response and the detection limits for the two detectors for the three analytes are measured. A comparison of the values obtained for serum extracts shows good agreement between the absorbance and electrochemical detectors.

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.

Organic electrochemical techniques having potential clinical application.

The Organic Electrochemistry Group at the National Bureau of Standards is pursuing several avenues of research of potential application to problems of clinical chemists. With one development, electrochemical detectors for liquid chromatography, organomercury species can be determined in biological tissues and other matrices. Spectroelectrochemistry is being used to characterize the redox behavior of metal complexes of bleomycin, an antitumor drug. Chemically modified electrodes are being developed as selective electrocatalytic sensors for organohalogen compounds and may lead to new sensors for clinically important analytes. Surface-enhanced Raman spectroscopy is helping characterize the polymer films used to modify the electrode surfaces. Another sensor is being developed for the detection of carboxylic acids: after the photocatalytic oxidation of the acids at a semiconductor electrode, the carbon dioxide produced is subsequently determined with a flow-through gas-sensing electrode. Finally, mathematical modeling may provide a better understanding of the fundamental processes involved in several of the above techniques.

Preconcentration and determination of cadmium in water by reversed-phase column chromatography and atomic absorption.

Studies were made of the solvent extraction of cadmium(II) from hydrochloric acid into a tri-n-octylamine-cyclohexene mixture. Distribution ratios, as a function of amine and acid concentration, were determined and this information was used to establish optimum extraction conditions and the probable nature of the extracted species. This system was used as the basis for the development of a reversed-phase column chromatographic technique for preconcentrating Cd(II). The amine-cyclohexene phase was coated on an inert macroreticular resin (XAD-2) to provide a stable column. With this system, Cd(II) in acidified water samples as large as 31. may be concentrated to 10 ml and determined by conventional atomic absorption. Interferences were studied, and the method was applied to the analysis of fresh-water streams for Cd(II).