Scott D. Harvey

Analysis of 2,4,6-trinitrotoluene and its transformation products in soils and plant tissues by high-performance liquid chromatography

Abstract Previous studies have failed to provide an acceptable mass balance for 2,4,6-trinitrotoluene (TNT) in soils and plants due to deficiencies in analytical methodology. A high-performance liquid chromatographic (HPLC) method for soil analysis is reported which allowed for a mass balance in excess of 88% during a 2-month study. A method for plant analysis was developed which involved fractionation of organic extracts on Florisil adsorbent, to remove interfering pigments, followed by HPLC analysis of TNT and the primary metabolites, 2-amino-4,6-dinitrololuene and 4-amino-2,6-dinitrotoluene. Chromatographic recovery of TNT from spiked tissues was 85 ± 6%. The methodology was utilized to investigate TNT uptake and metabolism in plants grown in TNT hydroponic solutions.

Blind field test evaluation of Raman spectroscopy as a forensic tool

Analytical instrumentation for Raman spectroscopy has advanced rapidly in recent years to the point where commercial field-portable instruments are available. Raman analysis with portable instrumentation is a new capability that can provide emergency response teams with on-site evaluation of hazardous materials. Before Raman analysis is accepted and implemented in the field, realistic studies applied to unknown samples need to be performed to define the reliability of this technique. Studies described herein provide a rigorous blind field test that utilizes two instruments and two operators to analyze a matrix that consists of 58 unknown samples. Samples were searched against a custom hazardous materials reference library (Hazardous Material Response Unit (HMRU) Spectral Library Database). Experimental design included a number of intentionally difficult situations including binary solvent mixtures and a variety of compounds that yield medium-quality spectra that were not contained in the HMRU library. Results showed that over 97% of the samples were correctly identified with no occurrences of false positive identifications (compounds that were not in the library were never identified as library constituents). Statistical analysis indicated equivalent performance for both the operators and instruments. These results indicate a high level of performance that should extrapolate to actual field situations. Implementation of Raman techniques to emergency field situations should proceed with a corresponding level of confidence.

Selective Stationary Phase for Solid-Phase Microextraction Analysis of Sarin (GB)

A number of critical field applications require monitoring air samples for trace levels of chemical warfare agents. Solid-phase microextraction (SPME) is a convenient format to conduct these analyses. Measurements could be significantly improved if a SPME phase selective for nerve agents were substituted for non-selective polymers typically used (e.g., polydimethylsiloxane). This paper evaluates a novel stationary phase, previously developed for methylphosphonate sensor applications, for use with SPME sampling. The phenol-based polymer, BSP3, was found to offer far higher selectivity toward sarin (GB) than polydimethylsiloxane due to a pronounced affinity toward the target analyte and a lower affinity toward hydrocarbons.

Rapid on-line chromatographic determination of trace-level munitions in aqueous samples

Abstract An on-line trace enrichment system is described that combines a divinylbenzene-vinylpyrrolidone co-polymer precolumn with a reversed-phase C18 HPLC analytical column. This arrangement allows quantitative preconcentration of munitions on the resin sorbent, followed by complete transfer of analyte to the analytical column for separation, followed by UV absorbance detection at 254 nm. Detection limits were approximately 0.10 ng/ml for TNT and RDX when 10 ml of sample was analyzed. The feasibility of increasing sample volume (up to 50 ml) to obtain detection limits down to 20 pg/ml was also demonstrated for TNT. Analyses of aquifer samples collected in the vicinity of a military installation are presented to show system utility.

Capillary zone electrophoretic and micellar electrokinetic capillary chromatographic separations of polyaminopolycarboxylic acids as their copper complexes

Abstract Capillary zone electrophoretic (CZE) and micellar electrokinetic capillary chromatographic (MECC) separations with UV absorbance detection at 290 nm were developed for separation and detection of the negatively-charged copper complexes of the polyaminopolycarboxylic acids. A standard mixture that contained ethylenediaminetetraacetic (EDTA), nitrilotriacetic (NTA), ethylenediaminetriacetic (ED3A), diethylenetriaminepentaacetic (DPTA) and hydroxyethylenediaminetriacetic (HEDTA) acids was utilized to demonstrate these separation methods. MECC techniques were performed with either cationic (cetyltrimethylammonium bromide, CTAB) or anionic (sodium dodecyl sulfate, SDS) surfactants. All three separation techniques achieved separation of the standard components with baseline resolution. A fast separation (7.5 min) was obtained with CTAB surfactant that provided a detection limit of 38 pg for HEDTA. The cationic micellar strategy was also extended to separations of mixed-metal EDTA complexes.

Characterization of Diesel Fuel by Chemical Separation Combined with Capillary Gas Chromatography (GC) Isotope Ratio Mass Spectrometry (IRMS)

The purpose of this study was to perform a preliminary investigation of compound-specific isotope analysis (CSIA) of diesel fuels to evaluate whether the technique could distinguish diesel samples from different sources/locations. The ability to differentiate or correlate diesel samples could be valuable for discovering fuel tax evasion schemes or for environmental forensic studies. Two urea adduction-based techniques were used to isolate the n-alkanes from the fuel. Both carbon isotope ratio (δ(13)C) and hydrogen isotope ratio (δD) values for the n-alkanes were then determined by CSIA in each sample. The samples investigated had δ(13)C values that ranged from -30.1‰ to -26.8‰, whereas δD values ranged from -83‰ to -156‰. Plots of δD versus δ(13)C with sample n-alkane points connected in order of increasing carbon number gave well-separated clusters with characteristic shapes for each sample. Principal components analysis (PCA) with δ(13)C, δD, or combined δ(13)C and δD data was applied to extract the maximum information content. PCA scores plots could clearly differentiate the samples, thereby demonstrating the potential of this approach for distinguishing (e.g., fingerprinting) fuel samples using δ(13)C and δD values.

Evaluation of Copper-1,3,5-benzenetricarboxylate Metal-organic Framework (Cu-MOF) as a Selective Sorbent for Lewis-base Analytes

The metal-organic framework copper-1,3,5-benzenetricarboxylate (Cu-BTC) was evaluated for its ability to selectively interact with Lewis-base analytes by examining retention on gas-chromatographic columns packed with Chromosorb W HP that contained 3.0% SE-30 along with various loadings of Cu-BTC. Scanning electron microscopy images of the support material showed the characteristic Cu-BTC crystals embedded in the SE-30 coating on the diatomaceous support. The results indicated that the Cu-BTC-containing stationary phase had limited thermal stability (220 °C) and strong general retention for analytes. Kováts index calculations showed selective retention (amounting to about 300 Kováts units) relative to n-alkanes for many small Lewis-base analytes on a column that contained 0.75% Cu-BTC compared with an SE-30 control. Short columns that contained lower loadings of Cu-BTC (0.10%) allowed elution of nitroaromatics; however, selectivity was not observed for aromatic compounds (including nitroaromatics) or nitroalkanes. Observed retention characteristics are discussed.

Determination of the explosive 2,4,6-trinitrophenylmethylnitramine (tetryl) and its transformation products in soil

Abstract Soils amended with uniformly ring-labeled [14C]-2,4,6-trinitrophenylmethylnitramine (tetryl) were subjected to exhaustive Soxhlet extraction followed by high-performance liquid chromatographic analysis immediately after amendment and at 11, 30, and 60 days post-amendment. Transformation of tetryl was found to be extremely rapid. Tetryl was below the detection limit in soil extracts by 30 days post-amendment. Radiochromatographic profiles revealed the presence of a variety of transformation products. The primary transformation product appeared in soil extracts immediately after amendment and was subsequently identified as N-methyl-2,4,6-trinitroaniline. A minor transformation pathway was identified that involved direct ring nitro reduction of tetryl, resulting in the production of an aminodinitrophenylmethylnitramine isomer. The mass balance of the soil system was greater than 79% over the 60-day study, with 43% of the amended radiolabeled found to be non-extractable at the conclusion of the study.

Safety Considerations for Sample Analysis Using a Near-Infrared (785 nm) Raman Laser Source

Raman spectroscopy is often considered a nondestructive analytical technique; however, this is not always the case. The 300-mW 785-nm near-infrared (NIR) laser source used with many commercially available instruments has sufficient power to burn samples. This destructive potential is of special concern if the sample is irreplaceable (e.g., fine art, forensic evidence, or for in vivo medical diagnostics) or a hazardous energetic material (explosive or pyrophoric samples). This study quantifies the heat resulting from illuminating an extensive color array with a 785-nm NIR laser and relates these values to the hazards associated with Raman analysis. In general, darker colors were found to be more problematic. Since visible colors are not ideally correlated with absorptive characteristics at 785 nm, predictions based on thermography are not perfect; however, this approximation gives a useful method for predicting the thermal response of unknown samples to NIR exposure. Additionally, experimental studies evaluated the analysis of flammable organic solvents, propellants, military explosives, mixtures containing military explosives, shock-sensitive explosives, and gunpowders (i.e., smokeless, black, and Pyrodex powders). Safety guidelines for analysis are presented.

Analysis of the explosive 2,4,6-trinitrophenylmethylnitramine (tetryl) in bush bean plants

Abstract Previous attempts to delineate the metabolism of the explosive 2,4,6-trinitrophenylmethylnitramine (tetryl) in plants have been unsuccessful. Development of an appropriate analytical methodology has been thwarted due to the extreme thermal and base lability of tetryl as well as its propensity to undergo photodecomposition. This study presents a methodology based on solvent extraction of plant tissue followed by fractionation of the organic extract on silica gel with subsequent determination of tetryl by HPLC. This methodology allowed 82.70 ± 5.54% recovery of tetryl from fortified bush bean leaves. The developed methodology was applied to study tetryl uptake and metabolism in bush bean plants exposed to tetryl-amended hydroponic cultures.