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Quantico Station, VA, United States

Muehlethaler C.,University of Lausanne | Massonnet G.,University of Lausanne | Deviterne M.,University of Lausanne | Bradley M.,Chemistry Unit | And 12 more authors.
Forensic Science International | Year: 2013

This study represents the most extensive analysis of batch-to-batch variations in spray paint samples to date. The survey was performed as a collaborative project of the ENFSI (European Network of Forensic Science Institutes) Paint and Glass Working Group (EPG) and involved 11 laboratories. Several studies have already shown that paint samples of similar color but from different manufacturers can usually be differentiated using an appropriate analytical sequence. The discrimination of paints from the same manufacturer and color (batch-to-batch variations) is of great interest and these data are seldom found in the literature. This survey concerns the analysis of batches from different color groups (white, papaya (special shade of orange), red and black) with a wide range of analytical techniques and leads to the following conclusions. Colored batch samples are more likely to be differentiated since their pigment composition is more complex (pigment mixtures, added pigments) and therefore subject to variations. These variations may occur during the paint production but may also occur when checking the paint shade in quality control processes. For these samples, techniques aimed at color/pigment(s) characterization (optical microscopy, microspectrophotometry (MSP), Raman spectroscopy) provide better discrimination than techniques aimed at the organic (binder) or inorganic composition (fourier transform infrared spectroscopy (FTIR) or elemental analysis (SEM - scanning electron microscopy and XRF - X-ray fluorescence)). White samples contain mainly titanium dioxide as a pigment and the main differentiation is based on the binder composition (C-H stretches) detected either by FTIR or Raman. The inorganic composition (elemental analysis) also provides some discrimination. Black samples contain mainly carbon black as a pigment and are problematic with most of the spectroscopic techniques. In this case, pyrolysis-GC/MS represents the best technique to detect differences. Globally, Py-GC/MS may show a high potential of discrimination on all samples but the results are highly dependent on the specific instrumental conditions used. © 2013 Elsevier Ireland Ltd. Source


Faparusi F.,Biology Unit | Bello-Akinosho M.M.,Biology Unit | Oyede R.T.,Chemistry Unit | Adewole A.,Biology Unit | And 2 more authors.
Research Journal of Phytochemistry | Year: 2012

Brillantaisia patula is a medicinal plant used for different ailments in Africa. Phytochemical constituents and antibacterial potential of the plant were investigated. In vitro antibacterial activity using agar-well diffusion method was carried out against Staphylococcus aureus (ATCC 25923), Enterococcus faecalis (ATGC 24212), Proteus hauseri (ATCG 13315), Pseudomonas aeruginosa ATCC 27853 and Escherichia coli (ATCC 38218). The phytochemistry of both methanol and ethanol extracts of Brillantaisia patula leaf revealed the presence of alkaloids, glycosides, terpenoids, steroids, flavonoids, tannins, steroids, flavonoids and saponins. Terpenoids and flavonoids were found in the methanolic extract but not in the ethanolic extract while steroid was found in the ethanolic extract but not in the methanolic extract. The ethanolic extract was active against all the five pathogenic bacteria while the methanolic extract inhibited all the test bacteria but Staphylococcus aureus. Ethanolic extract zones of inhibition ranged from 15.3±0.6 to 20.7±0.6 mm, whereas methanolic extract zones of inhibition ranged from 18.0±1.0 to 30.0±1.0 mm. The Minimum Inhibitory Concentration (MIC) of ethanolic extract ranged from 25 to 200 mg mL -1 while that of methanolic extract was from 50 to 100 mg mL -1. The Minimum Bactericidal Concentration (MBC) of methanolic extract ranged from 100 to 200 mg mL -1. The least MBC value (50 mg mL -1) of ethanolic extract was against Escherichia coli while the highest value (>200 mg mL -1) was against Proteus hauseri. Leaf of Brillantaisia patula could be a novel source of antibacterial agent (s) that might have broad spectrum activity. © 2012 Academic Journals Inc. Source


Mehltretter A.H.,Chemistry Unit | Parish A.,Latent Prints Operations Unit
Science and Justice | Year: 2012

Forensic interest in adhesive tapes with polyvinyl chloride (PVC) backings (electrical tape) derives from their use in a variety of illicit activities. Due to the range of physical characteristics, chemical compositions, and homogeneity within a single roll of tape, traditional microscopic and chemical analyses can offer a high degree of discrimination between tapes, permitting the assessment of potential associations between evidentiary tape samples. The carbon isotope ratios of tapes could provide additional discrimination among tape samples. To evaluate whether carbon isotope ratios may be able to increase discrimination of electrical tapes, particularly with regards to different rolls of tape of the same product, we assessed the δ 13C values of backings from 87 rolls of PVC-based black electrical tape (~20 brands, >60 products) Prior to analysis, adhesives were removed to prevent contamination by adhering debris, and plasticizers were extracted because of concern over their potential mobility. This result is consistent with each of these tapes having approximately the same plasticizer δ 13C value and proportion of carbon in these plasticizers. The δ 13C values of the 87 PVC tape backings ranged between -23.5 and -41.3 (‰, V-PDB), with negligible carbon isotopic variation within single rolls of tape, yet large variations among tape brands and tape products. Within this tape population, carbon isotope ratios permitted an average exclusion power of 93.7%, using a window of +/-0.3‰; the combination of carbon isotope ratio measurement with additional chemical and physical analyses raises the discrimination power to over 98.9%, with only 41 out of a possible 3741 pairs of tape samples being indistinguishable. There was a linear relationship between the δ 13C value of tape backings and the change in δ 13C value with the extraction of plasticizers. Analyses of pre- and post-blast tape sample pairs show that carbon isotope signatures are within 0.3‰ of pre-blast values, indicating that carbon isotope values are largely preserved during an explosion. © 2011. Source


Olumayede E.G.,Chemistry Unit | Okuo J.M.,University of Benin
Polish Journal of Environmental Studies | Year: 2012

The living patterns of people may create different variations in concentrations of air pollutants in urban setting. Ambient VOCs measured in the Nigerian urban center of Benin City were analyzed and evaluated for variation characteristics; spatial, seasonal, and diurnal patterns of air pollutants. For this purpose samples were collected (from June 2009 to May 2010) at seven locations selected to represent local activities in the city. To determine the diurnal pattern of VOCs, four hourly samplings were carried out at six-day intervals. Samples were analyzed using gas chromatography. Among the VOC species detected are 4 alkanes, 6 aromatic compounds, 4 chlorinated hydrocarbons, and 1ketone. The results showed that ambient VOC levels in the atmosphere of Benin City are driven by high traffic; hence high concentrations were observed in most traffic junctions sampled. The examination of the average of total VOC accumulation showed significant spatial and easonal variability (p<0.01) in all sites. The diurnal pattern showed higher concentrations in the morning, and then evening, indicating that fresh emissions impact the air mass in the city. Analyses of the weekly variations of the pollutants showed the weekday's maxima and the weekend's minima, an indication of traffic influence. Source


Bentley T.W.,Chemistry Unit | Koo I.S.,Korea National University of Education
Arkivoc | Year: 2012

Rate constants are reported at 25 °C for solvolyses of p-Z-substituted benzoyl chlorides (Z = O2N, Cl, H, Me, and MeO) in 2,2,2-trifluoroethanol (TFE) in binary mixtures with water or ethanol. Product selectivities (kTFE/kwater) are also reported. Previous work in which rate constants for solvolyses of benzoyl chlorides are correlated with σ constants is re-evaluated. V-shaped plots (assuming concurrent reactions) are constructed from logarithms of rate constants vs. σ (not σ ) for substituent effects or a suitable parameter for solvent effects. Conditions are established for which it is predicted that concurrent mechanisms (one dissociative, one associative) each contribute 50% towards the observed rate constants. © ARKAT-USA, Inc. Source

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