Improvement of EPA method 8330: complete separation using a two-phase approach

Evaluation of various natural weeds and reaction conditions for reductive degradation of 1,3-dinitrobenzene

1,3-Dinitrobenzene (1,3-DNB) is listed by the USEPA as a priority pollutant. 1,3-DNB has two nitro functional groups (-NO₂) bound to the benzene ring, with a +III nitrogen oxidation states, and strong electronegativity, and therefore can be reductively degraded by gaining electrons. Weeds that contain a high proportion of polyphenols can supply electrons and act as natural reducing agents. This study investigated the potential of various weeds to reductively remove 1,3-DNB from aqueous phase. The Taguchi L9 Orthogonal experimental design method was used to explore the optimum operational parameters. According to the analyzed characteristics of weeds, including total phenol content, antioxidant capacity, metal chelating capacity, reducing capacity, and environmental adaptability, the weed Sphagneticola trilobata, containing 11.93 mg of gallic acid equivalent per gram of weed (mg-GAE/g-weed), was selected for 1,3-DNB degradation experiments. The results showed that the optimum reaction conditions for the degradation of 1,3-DNB in the aqueous phase using Sphagneticola trilobata were: pH 3, a weed dose of 10 g/L, reaction time of 14 day, and initial 1,3-DNB concentration of 0.5 mM. According to ANOVA analysis, the weed dose was the most significant factor in the experiment, and each 1 mg of 1,3-DNB degraded required 120 mg of dry weeds.

Highly sensitive determination of 2,4,6-trinitrotoluene and related byproducts using a diol functionalized column for high performance liquid chromatography

In this work, a new detection method for complete separation of 2,4,6-trinitrotoluene (TNT); 2,4-dinitrotoluene (2,4-DNT); 2,6-dinitrotoluene (2,6-DNT); 2-aminodinitrotoluene (2-ADNT) and 4-aminodinitrotoluene (4-ADNT) molecules in high-performance liquid-chromatography (HPLC) with UV sensor has been developed using diol column. This approach improves on cost, time, and sensitivity over the existing methods, providing a simple and effective alternative. Total analysis time was less than 13 minutes including column re-equilibration between runs, in which water and acetonitrile were used as gradient elution solvents. Under optimized conditions, the minimum resolution between 2,4-DNT and 2,6-DNT peaks was 2.06. The recovery rates for spiked environmental samples were between 95-98%. The detection limits for diol column ranged from 0.78 to 1.17 µg/L for TNT and its byproducts. While the solvent consumption was 26.4 mL/min for two-phase EPA and 30 mL/min for EPA 8330 methods, it was only 8.8 mL/min for diol column. The resolution was improved up to 49% respect to two-phase EPA and EPA 8330 methods. When compared to C-18 and phenyl-3 columns, solvent usage was reduced up to 64% using diol column and resolution was enhanced approximately two-fold. The sensitivity of diol column was afforded by the hydroxyl groups on polyol layer, joining the formation of charge-transfer complexes with nitroaromatic compounds according to acceptor-donor interactions. Having compliance with current requirements, the proposed method demonstrates sensitive and robust separation.

Ion spectrometric detection technologies for ultra-traces of explosives: a review

In recent years, explosive materials have been widely employed for various military applications and civilian conflicts; their use for hostile purposes has increased considerably. The detection of different kind of explosive agents has become crucially important for protection of human lives, infrastructures, and properties. Moreover, both the environmental aspects such as the risk of soil and water contamination and health risks related to the release of explosive particles need to be taken into account. For these reasons, there is a growing need to develop analyzing methods which are faster and more sensitive for detecting explosives. The detection techniques of the explosive materials should ideally serve fast real-time analysis in high accuracy and resolution from a minimal quantity of explosive without involving complicated sample preparation. The performance of the in-field analysis of extremely hazardous material has to be user-friendly and safe for operators. The two closely related ion spectrometric methods used in explosive analyses include mass spectrometry (MS) and ion mobility spectrometry (IMS). The four requirements-speed, selectivity, sensitivity, and sampling-are fulfilled with both of these methods.

Development of a new SPME-HPLC-UV method for the analysis of nitro explosives on reverse phase amide column and application to analysis of aqueous samples

A rapid, simple, sensitive and accurate quantitative method has been developed for the determination of eleven nitroaromatic components by solid phase microextraction (SPME) coupled to high performance liquid chromatography (HPLC) with UV detection from aqueous samples. PDMS/DVB resin fiber (60 microm) was used for concurrent extraction of all the analytes from aqueous matrix. Static desorption was carried out in the desorption chamber of SPME-HPLC interface containing mobile phase; methanol:water 43:57 (v/v) with subsequent liquid chromatographic analysis at isocratic flow rate of 1.3 mL/min and detection at 254 nm. A reverse phase amide column (5 microm) was used as a separation medium. The limit of detection (S/N=3) for TNT and Tetryl was found to be 0.35 and 0.54 ng/mL, respectively. Developed method has been applied successfully to the analysis of aqueous samples obtained from environmental and industrial sources like river water, ground water, drinking water and industrial waste water.

Use of porous graphitic carbon for the analysis of nitrate ester, nitramine and nitroaromatic explosives and by-products by liquid chromatography–atmospheric pressure chemical ionisation-mass spectrometry

A new LC/MS method was developed for the analysis of sixteen different analytes including the most common organic explosives encountered in forensic investigations. The separation was achieved using a porous graphitic carbon (PGC) column with a binary gradient elution. Molecular modeling suggested a possible interpretation for the elution order of explosive compounds on PGC. The introduction of ammonium formate in the mobile phase resulted in the formation of characteristic adduct ions thus enhancing the mass spectrometric detection of nitrate ester and nitramine compounds. Atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) were compared in terms of sensitivity. The final LC/APCI-MS method allowed easy identification of investigated compounds with limits of detection ranging from 0.04 to 1.06 ng/microl. The analysis of simulated forensic samples confirmed the performance of the method.

Development of new rat monoclonal antibodies with different selectivities and sensitivities for 2,4,6-trinitrotoluene (TNT) and other nitroaromatic compounds

Five new rat monoclonal antibodies (mAbs) for 2,4,6-trinitrotoluene (TNT) and other nitroaromatic compounds, including, especially, the metabolite 2-amino-4,6-dinitrotoluene (2-ADNT), are described. Five heterogeneous, competitive enzyme-linked immunosorbent assays (ELISAs) were developed. Assay 1 uses mAb DNT4 3F6 as recognition element and gives a standard curve for TNT in 40 mmol L(-1) phosphate buffered saline (PBS) with a test midpoint (IC50) of 0.26+/-0.08 microg L(-1) (n=20). Assay 2 (mAb DNT4 4G4) has an IC50 of 0.35+/-0.07 microg L(-1) (n=18), assay 3 (mAb DNT4 1A3) has an IC50 of 0.73+/-0.14 microg L(-1) (n=15), and assay 4 (mAb DNT4 1A7) has an IC50 of 2.32+/-0.70 microg L(-1) (n=15). Assay 5 (mAb DNT2 4B4) is very selective for 2-ADNT and has an IC50 of 8.5+/-1.7 microg L(-1) (n=15) in PBS. These antibodies for nitroaromatic compounds differ not only in their sensitivity but also in their selectivity. Major cross-reactants are 1,3,5-trinitrobenzene, 2-ADNT, 4-amino-2,6-dinitrotoluene (4-ADNT), 2,4-dinitroaniline, 3,5-dinitroaniline, and 2,6-dinitroaniline. Although assay 5 is not highly sensitive, the mAb DNT2 4B4 in this assay is highly selective for 2-ADNT. Of all the compounds tested, only 2,4-dinitroaniline and 3,5-dinitroaniline had relevant cross reactivities, 18% and about 26%, respectively. Two ELISAs, using mAbs DNT4 3F6 and DNT2 4B4, were used to analyze different concentrations of TNT and 2-ADNT, respectively, in three different surface water matrices (river and lake water). Both assays were affected by the matrix, but usually performed well (recovery within the range 70-120%). In addition, these ELISAs were used to analyze mixtures of TNT, 2-ADNT, and 4-ADNT, at three different concentrations, in the same water matrices. A different recognition pattern was clearly visible with both assays and depended on the cross reactivities of the corresponding mAb.

Use of reversed-phase high-performance liquid chromatography-diode array detection for complete separation of 2,4,6-trinitrotoluene metabolites and EPA Method 8330 explosives: influence of temperature and an ion-pair reagent

Explosives such as 2,4,6-trinitrotoluene (TNT), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) are widely distributed environmental contaminants. Complete chromatographic separation is necessary in order to accurately determine and quantify explosives and their degradation products in environmental samples and in (bio)transformation studies. The present study describes a RP-HPLC method with diode array detection using a LC-8 guard column, a Supelcosil LC-8 chromatographic column, and a gradient elution system. This gradient method is capable of baseline separating the most commonly observed explosives and TNT transformation metabolites including 2,4,6-triaminotoluene (TAT) in a single run. The TNT metabolites separated were 2-hydroxylamino-4,6-dinitrotoluene, 4-hydroxylamino-2,6-dinitrotoluene, 2,4-dihydroxylamino-6-nitrotoluene, 4,4',6,6'-tetranitro-2,2'-azoxytoluene, 2,2',6,6'-tetranitro-4,4'-azoxytoluene, 4,4',6,6'-tetranitro-2,2'-azotoluene, 2,2',6,6'-tetranitro-4,4'-azotoluene, 2-amino-4,6-dinitrotoluene, 4-amino-2, 6-dinitrotoluene, 2,6-diamino-4-nitrotoluene, 2,4-diamino-6-nitrotoluene, and TAT. The same gradient method at a different column temperature can also be used to baseline separate the explosives targeted in the Environmental Protection Agency (EPA) Method 8330 with approximately 22% reduction in total run time and 48% decrease in solvent consumption compared to previously published methods. Good separation was also obtained when all TNT metabolites and EPA Method 8330 compounds (a total of 23 compounds) were analyzed together; only 2,6-DANT and HMX co-eluted in this case. The influence of temperature (35-55 degrees C) and the use of an ion-pair reagent on the chromatographic resolution and retention were investigated. Temperature was identified as the key parameter for optimal baseline separation. Increased temperature resulted in shorter retention times and better peak resolution especially for the aminoaromatics investigated. The use of an ion-pair reagent (octanesulfonic acid) generally resulted in longer retention times for compounds containing amine functional groups, more baseline noise, and decreased peak resolution.

Comparison of chromatographic properties of cyanopropyl-, diol- and aminopropyl- polar-bonded stationary phases by the retention of model compounds in normal-phase liquid chromatography systems

Polar-bonded stationary phases, such as CN-, diol- and NH2-silica, have been characterised by the retention of model solutes (phenols, aromatic amines and quinoline bases) in normal-phase systems using n-heptane--polar modifier (2-propanol, tetrahydrofuran or dioxane) mixtures as eluents. The selectivity of separation for the particular groups of substances has been analysed by the log kI versus log kII relationships for CN- and diol, CN- and NH2- and NH2- and diol phases in examined eluent systems by the plotting of correlation lines. The values of regression coefficient r indicate either the similarity of the retention mechanisms of model solutes in some examined systems where r>0.9, or differences among various systems where r<<0.9. The values of slopes of correlation lines show the selectivity of separation for particular group of compounds. The selectivity of separation has also been characterised by deltalog k values. The effect of modifier (2-propanol, tetrahydrofuran and dioxane) on selectivity of model solutes on these phases has also been discussed.