Christopher R. Dockery

Speciation of Chromium via Laser-Induced Breakdown Spectroscopy of Ion Exchange Polymer Membranes

A new method for the speciation of ng/mL concentrations of Cr(III) and Cr(VI) solutions with analysis by laser-induced breakdown spectroscopy (LIBS) is reported. Speciation is achieved by pre-concentration of the chromium onto commercially available cation exchange polymer membranes. Chromium(III) is removed directly by cation exchange; chromium(VI) in the filtrate is reduced to Cr(III) and concentrated onto a second cation exchange membrane, affording independent measurement of both species. Large volumes of waters containing Cr(III) and Cr(VI) can be concentrated onto the membranes and directly analyzed by laser-induced breakdown spectroscopy. The estimated limit of detection corresponds to 500 ng of Cr on the membrane: if a solution volume of 1 L is used, then the detection limit corresponds to a solution concentration of 0.5 ng/mL. Excellent separation of the chromium species is attained. Results show that overall method efficiencies range from 94–116% and are independent of the matrix. The influence of pH has been measured, and although Cr(VI) converts to Cr(III) in acidic solutions, the total Cr recoveries are not appreciably influenced by pH over the range of natural waters (4 to 9). In addition, speciation was performed in the presence of a number of different cations and showed that the method is robust in many different and complex matrices.

Laser-induced breakdown spectroscopy for the detection of gunshot residues on the hands of a shooter

Laser-induced breakdown spectroscopy (LIBS) has been used to determine whether the hands of a suspected gun user contain traces of gunshot residue. Samples are obtained by pressing adhesive tape against the skin of the suspect and analyzing the tape directly. When the suspect has fired multiple shots, or if the gun has not been cleaned, the gunshot residue provides a spectral signature that is readily apparent, but a person who has fired a single shot from a clean gun is not so easy to identify. The error rates associated with the LIBS identification of a subject who fired one shot from a clean gun have been evaluated by Monte Carlo simulation techniques, and criteria are proposed for defining a positive or a negative test result.

Determining the Lifetime of Detectable Amounts of Gunshot Residue on the Hands of a Shooter Using Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) has been used to determine the period of time that a shooter will test positive for gunshot residue (GSR) after firing a revolver. Multiple rounds of primer were fired and samples collected at multiple hour intervals using an adhesive tape pressed against the skin. Samples were analyzed directly using a commercially available laser-induced breakdown spectrometer where barium emission (originating from barium nitrate in the primer) was observed. Population statistics were used to compare suspected GSR to a library of blank samples from which a threshold value was established. Statistically significant results, positive for GSR, are obtained 5.27 days after a firearm discharge using these techniques.

Detecting gunshot residue by laser induced breakdown spectroscopy

Laser induced breakdown spectroscopy was used to detect gunshot residue (GSR) on a shooter’s hand. Double sided tape pressed to the skin of the shooter was directly analyzed. Characteristic emission lines identified GSR presence.

Antibacterial Activities of Wasabi Against Escherichia coli O157:H7 and Staphylococcus aureus

Escherichia coli O157:H7 and Staphylococcus aureus are two of the major pathogens frequently involved in foodborne outbreaks. Control of these pathogens in foods is essential to food safety. It is of great interest in the use of natural antimicrobial compounds present in edible plants to control foodborne pathogens as consumers prefer more natural “green” foods. Allyl isothiocyanate (AITC) is an antimicrobial compound naturally present in wasabi (Japanese horseradish) and several other edible plants. Although the antibacterial effects of pure AITC and wasabi extract (essential oil) against several bacteria have been reported, the antibacterial property of natural wasabi has not been well studied. This study investigated the antibacterial activities of wasabi as well as AITC against E. coli O157:H7 and S. aureus. Chemical analysis showed that AITC is the major isothiocyanate in wasabi. The AITC concentration in the wasabi powder used in this study was 5.91 ± 0.59 mg/g. The minimum inhibitory concentration (MIC) of wasabi against E. coli O157:H7 or S. aureus was 1% (or 10 mg/ml). Wasabi at 4% displayed higher bactericidal activity against S. aureus than against E. coli O157:H7. The MIC of AITC against either pathogen was between 10 and 100 μg/ml. AITC at 500 μg/ml was bactericidal against both pathogens while AITC at 1000 μg/ml eliminated E. coli O157:H7 much faster than S. aureus. The results from this study showed that wasabi has strong antibacterial property and has high potential to effectively control E. coli O157:H7 and S. aureus in foods. The antibacterial property along with its natural green color, unique flavor, and advantage to safeguard foods at the point of ingestion makes wasabi a promising natural edible antibacterial plant. The results from this study may be of significant interest to the food industry as they develop new and safe foods. These results may also stimulate more research to evaluate the antibacterial effect of wasabi against other foodborne pathogens and to explore other edible plants for their antimicrobial properties. To our knowledge, this is the first report on the antibacterial activity of wasabi in its natural form of consumption against E. coli O157:H7 and S. aureus.

Gunshot Residue Analysis in the Undergraduate Laboratory Using Toy Cap Guns

ABSTRACT The authors developed an experiment for the undergraduate analytical or forensic chemistry laboratory in which gunshot residues (GSRs) produced from toy cap guns are analyzed by laser-induced breakdown spectroscopy (LIBS). Alternatively, the experiment is readily adaptable to any emission spectroscopy technique. This project allows students to investigate the development of a forensic method while addressing proper sampling techniques used in forensic investigations. Students were able to develop a library of blank samples, establish signal detection limits to address legal considerations for determination of false-positive and -negative error rates, and optimize an emission spectrometer.

Thermogravimetric Analysis of Target Inhibitors for the Spontaneous Self-Heating of Coal

ABSTRACT Self-oxidation of coal can result in spontaneous combustion events at any time during mining, transporting, or processing causing environmental, economical, and safety concerns. Spontaneous coal combustion is a naturally occurring phenomenon that often causes damage to industrial and commercial facilities and freight, reduces the caloric value of coal, releases noxious gases and particulate matter, and increases pollution. As heat accumulates through self-oxidation, the internal temperature of the coal continues to rise over time and if left unaltered will lead to spontaneous coal fires. In this study, we investigated thermogravimetric properties of target compounds for the inhibition of the spontaneous self-heating of coal. Coal was treated with inorganic phosphate and sulfonate salts combined with anionic and non-ionic surfactant blends. Each ingredient was applied to the surface individually and systematically varied to reach a cost-effective and efficient formulation. Thermal and microscopic analyses were used to characterize these effects. Results showed that novel formulations can significantly increase the onset temperature for pyrolysis and oxidation of coal.

Laser-Induced Breakdown Spectroscopy for the Rapid Characterization of Lead-Free Gunshot Residues

This study investigated the use of laser-induced breakdown spectroscopy (LIBS) and scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDX) as means of characterizing gunshot residue (GSR) originating from commercially available lead-free rounds. Data from two experiments are presented in this work. One experiment focused on identifying prominent analytical markers present in lead-free GSR by LIBS while the other applied SEM-EDX to determine the degree of evidence preservation after LIBS analysis. Samples of GSR were collected via tape-lift method from the hands of volunteer shooters and instrumental analyses were conducted in triplicate. As a result, the lead-free ammunition analyzed in this work generated GSRs comprising primarily Ba, Al, Si, and/or K. Trace amounts of Ti, Fe, and S were also apparent in some compositions. Through SEM-EDX analysis, a spheroidal geometry consistent with traditional lead-containing GSR was observed. Additionally, it was determined that evidence is preserved after LIBS analysis which supports the implementation of LIBS as a rapid preliminary screening method followed by confirmatory testing via SEM-EDX on the preserved evidence.

Characterization of lead-free gunshot residue analogs

Modern forensic analyses of inorganic gunshot residues rely on the detection of three key elements from the primer: barium, antimony, and lead. However, recent environmental concerns are trending toward an industry-wide shift to the manufacture and distribution of lead-free ammunition. Consequently, this change will require new methods that can be used to fully characterize the composition of lead-free gunshot residues. Spectrochemical analysis of simulated lead-free gunshot residues, in a proof of concept study, was used to identify statistically significant analytical markers present in each composition by Laser-Induced Breakdown Spectroscopy. Rates of error associated with each simulation were determined by leave-one-out cross-validation. Laser-Induced Breakdown Spectroscopy proved to be an effective and rapid screening method in the analysis of simulations of lead-free gunshot residues prior to confirmatory testing by Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy.