Nitro-organic Compounds Research Articles

Non-aqueous onion like nano-carbons from waste diesel-soot used as FRET-based sensor for sensing of nitro-phenols

Herein, a simple-functionalization method is described to prepare the oleylamine functionalized non-aqueous version of onion-like nanocarbons (ONC-OA), where ONC was isolated from the waste pollutant soot exhausted from the diesel engine. The surface group analysis of ONC-OA has been investigated via Nuclear Magnetic Resonance and X-ray Photoelectron Spectroscopy. ONC-OA shows blue fluorescence with a quantum yield of ∼6% in tetrahydrofuran (THF). The fluorescence-based sensing applications of ONC-OA has been investigated for selective sensing of toxic aromatic nitro-phenols compounds (para-nitro, dinitro, and trinitro phenols) from the tested many nitro organic compounds. Based on the limit of detection values, ONC-OA shows much better results for tri-nitro phenol compared to di and mono nitrophenol. To understand the quenching mechanism, a time-resolved photoluminescence analysis of the sensor with and without the addition of quenchers is performed. The effective lowering in fluorescence lifetime of the sensor after the addition of quenchers concludes that the quenching observed is majorly due to the Förster Resonance Energy Transfer (FRET) mechanism. The real-life application of ONC-OA was analyzed by external spiking of N-PhOHs in soil samples.

Chemical-bath-deposited rutile TiO2 film for electrochemical detection of 2,4,6-trinitrotoluene

In this study, 2,4,6-trinitrotoluene (2,4,6-TNT) was detected electrochemically through cyclic voltammetry (CV) and differential pulse voltammetry (DPV) by using a rutile TiO2 layer under ambient conditions. To accomplish this, an electrode was fabricated in a short time by using the chemical bath deposition process under low-temperature conditions. A rutile TiO2 layer was grown on both fluorine-doped tin oxide and glass surfaces by using a precursor solution containing chloride ions. Following calcination, the crystallinity of the rutile phases in the TiO2 layer was enhanced. In the CV profiles (obtained over a potential range between −0.6 and −1.2 V (versus Ag/AgCl, 3 M KCl) in a 100 ppm 2,4,6-TNT solution under ambient conditions), the three main reduction peaks of 2,4,6-TNT were observed only for the calcined TiO2 layer owing to the increased crystallinity of the rutile phase and the increased active site density. Calcination facilitated high active site density, a large electrochemically active surface area, and short electrochemical reaction times under low charge transfer resistance, which were key for enhancing the performance of the rutile TiO2 layer as the electrode toward 2,4,6-TNT detection. The DPV results revealed that the limits of detection and quantitation were 10.8 ppm and 36.0 ppm, respectively, with a linear range of 10–100 ppm, for 2,4,6-TNT detection using the calcined TiO2 layer as the working electrode. The detection of 2,4,6-TNT using a crystallized transition metal without a noble metal support is an attractive approach that can be applied toward the detection of other explosive nitro-organic compounds such as nitroglycerin and pentaerythritol tetranitrate.

Abiotic reductive removal of organic contaminants catalyzed by carbon materials: A short review.

Since the observation that carbon materials can facilitate electron transfer between reactants, there is growing literature on the abiotic reductive removal of organic contaminants catalyzed by them. Most of the interest in these processes arises from the participation of carbon materials in the natural transformation of contaminants and the possibility of developing new strategies for environmental treatment and remediation. The combinations of various carbon materials and reductants have been investigated for the reduction of nitro-organic compounds, halogenated organics, and azo dyes. The reduction rates of a certain compound in carbon-reductant systems vary with the surface properties of carbon materials, although there are controversial conclusions on the properties governing the catalytic performance. This review scrutinizes the contributions of quinone moieties, electron conductivity, and other carbon properties to the activity of carbon materials. It also discusses the contaminant-dependent reduction pathways, that is, electron transfer through conductive carbon and intermediates formed during the reaction, along with possibly additional activation of contaminant molecules by carbon. Moreover, modification strategies to improve the catalytic activity for reduction are summarized. Future research needs are proposed to advance the understanding of reaction mechanisms and improve the practical utility of carbon material for water treatment. PRACTITIONER POINTS: Reduction rates of contaminants in carbon-reductant systems and modification strategies for carbon materials are summarized. Mechanisms for the catalytic activity of carbon materials are discussed. Research needs for new insights into carbon-catalyzed reduction are proposed.

Eco-friendly synthesis of lignin mediated silver nanoparticles as a selective sensor and their catalytic removal of aromatic toxic nitro compounds.

The development of an eco-friendly and reliable process for the production of nanomaterials is essential to overcome the toxicity and exorbitant cost of conventional methods. As such, a facile and green synthesis method is introduced for the preparation of lignin mediated silver nanoparticles (L-Ag NPs). This is produced by reducing Ag precursors using lignin biopolymers which are formulated by pulsed laser irradiation and an ultrasonication process. Lignin operates as both a reducing and stabilizing agent. The various analytical techniques of ultraviolet-visible spectroscopy, transmission electron microscope and X-ray diffractometer studies were employed to verify the formation of non-aggregated spherical L-Ag NPs with an average size as small as 7-8nm. The selective sensing capability of the synthesized L-Ag NPs was examined for the detection of hydrogen peroxide and mercury ions in an aqueous environment. Furthermore, the superior catalytic performance of L-Ag NPs was demonstrated by the rapid conversion of toxic 4-nitrophenol and nitrobenzene as targeted pollutants to the corresponding amino compounds. A plausible catalytic reduction mechanism for the removal of toxic nitro-organic pollutants over L-Ag NPs is proposed. This research coincides with existing studies and affirms that L-Ag NPs are an effective sensor that be applied as a catalytic material within environmental remediation and also alternative biomedical applications.

Bioremediation of Explosive TNT by Trichoderma viride.

Nitroaromatic and nitroamine compounds such as 2,4,6-trinitrotoluene (TNT) are teratogenic, cytotoxic, and may cause cellular mutations in humans, animals, plants, and microorganisms. Microbial-based bioremediation technologies have been shown to offer several advantages against the cellular toxicity of nitro-organic compounds. Thus, the current study was designed to evaluate the ability of Trichoderma viride to degrade nitrogenous explosives, such as TNT, by microbiological assay and Gas chromatography–mass spectrometry (GC–MS) analysis. In this study, T. viride fungus was shown to have the ability to decompose, and TNT explosives were used at doses of 50 and 100 ppm on the respective growth media as a nitrogenous source needed for normal growth. The GC/MS analysis confirmed the biodegradable efficiency of TNT, whereas the initial retention peak of the TNT compounds disappeared, and another two peaks appeared at the retention times of 9.31 and 13.14 min. Mass spectrum analysis identified 5-(hydroxymethyl)-2-furancarboxaldehyde with the molecular formula C6H6O3 and a molecular weight of 126 g·mol−1 as the major compound, and 4-propyl benzaldehyde with a formula of C10H12O and a molecular weight of 148 g mol−1 as the minor compound, both resulting from the biodegradation of TNT by T. viride. In conclusion, T. viride could be used in microbial-based bioremediation technologies as a biological agent to eradicate the toxicity of the TNT explosive. In addition, future molecular-based studies should be conducted to clearly identify the enzymes and the corresponding genes that give T. viride the ability to degrade and remediate TNT explosives. This could help in the eradication of soils contaminated with explosives or other toxic biohazards.

Selective catalytic reduction of NOx with ethanol and other C1–4 oxygenates over Ag/Al2O3 catalysts: A review

Research results regarding selective catalytic reduction (SCR) of NOx with ethanol and other C1-4 oxygenates as reductants over silver-alumina catalysts are summarized. The aspects of the process mechanism, nature of active sites, role of alumina and silver (especially in the formation of bifunctional active sites), effects of reductants and reaction conditions are discussed. It has been determined that key stages of the process include formation of reactive enolic species, their interaction with NOx and formation of nitroorganic compounds which transform to NCOads species and further to N2. The results obtained over various silver-alumina catalysts demonstrate the perspectives of their application for reducing the level of nitrogen oxides in engine emissions, including in the presence of water vapor and sulfur oxides. Ways to improve the catalysts for the SCR of NOx with C1-4 oxygenates are outlined.

Draft Genome Sequence of Aspergillus oryzae ATCC 12892.

ABSTRACTThe draft genome sequence of Aspergillus oryzae ATCC 12892 is presented here. A. oryzae produces 3-nitropropionic acid, which has been investigated with regard to understanding the biosynthesis of nitroorganic compounds.

Hydrogenation of Nitro and Unsaturated Organic Compounds over Catalysts Containing Nanosized Palladium Particles

The activity of palladium catalysts prepared on the basis of ZnO modified with polyethylene glycol (1 wt % Pd–PEG/ZnO) with molecular weights of 4000 and 6000 in the hydrogenation reaction of a series of nitro and unsaturated organic compounds has been studied. The catalysts are characterized by the formation of small metal particles with a size from 3 to 8 nm which uniformly coat the support surface. The results obtained have been compared to the catalytic properties of palladium-containing nanodiamonds and activated carbon under similar conditions.

Synthesis and Characterization of Water Stable ZnO Quantum Dots Based-Sensor for Nitro-Organic Compounds

Here we propose luminescent ZnO QDs synthesized by a simple method in an unusual, powerful and ‘green’ solvent at low temperature, for the detection of aniline (e.g. 4-nitroanilina) compounds in water environment. To provide aqueous stability, ZnO QDs have been capped by (3-aminopropyl)triethoxysilane (APTES). The synthesized ZnO QDs have been characterized using X-ray diffraction, Transmission Electron Microscopy, Raman, UV-visible, Photoluminescence and Infrared Spectroscopy. This study demonstrates that the as synthesized ZnO QDs are highly luminescent, emitting yellow colour when exposed to UV radiation. Under UV radiation the nanoparticles exhibit high sensitivity to the presence of nitro-compounds in solution when they have a zwitterionic structure, even at very low concentration. In particular, this property makes APTES capped ZnO QDs very effective as sensor for p-nitroaniline.

Investigation on VOC Emissions from Automobile Sources by Means of Online Mass Spectrometry

This study reviews recent research on volatile organic compound (VOC) emissions from motorized vehicle sources by means of online mass spectrometry. Chemical ionization is a powerful tool that usually permits soft ionization of chemical species and it allows the time-resolved measurement of multiple VOCs, even in complex samples where many kinds of VOCs coexist. The vehicular exhaust gasses are investigated using H3O+, NO+, Hg+, and CH3C(O)O− as a reagent ion in online chemical ionization mass spectrometry. The proton transfer using H3O+ as a reagent ion was used for the detection of nitro-organic compounds such as nitromethane and nitrophenol. The time-resolved measurement of the nitro-organic compounds in the laboratory experiments with a chassis dynamometer system revealed their emission properties, such as the dependence of the emissions as a function of vehicular velocity and acceleration/deceleration, as well as the effect of various types of exhaust gas treatment. The data regarding the nitromethane and nitrophenol emissions obtained in the field measurements were consistent with the results of the laboratory experiments done with a chassis dynamometer system. In the experiments involving evaporative emissions from gasoline-powered cars, NO+ was used as a reagent ion. Online measurements showed that the adsorption of hydrocarbons in a sealed housing evaporative determination unit could result in emissions being underestimated, if the concentrations are monitored only before and after a diurnal breathing loss test. The composition analysis gave an estimated ozone formation potential (OFP) approximately 20 % higher for breakthrough emissions and refueling emissions than for the gasoline that was tested, but the OFP for the permeation emissions was almost the same as the OFP for the test fuel.

Aqueous-phase story of isoprene – A mini-review and reaction with HONO

Isoprene is a major biogenic hydrocarbon emitted to the atmosphere and a well-recognized player in atmospheric chemistry, formation of secondary organic aerosol and air quality. Most of the scientific work on isoprene has focused on the gas-phase and smog chamber processing while direct aqueous chemistry has escaped the major attention because physical solubility of isoprene in water is low. Therefore, this work recollects the results of genuine research carried on atmospherically relevant aqueous-phase transformations of isoprene. It clearly shows that isoprene dissolves in water and reacts in aqueous solutions with common atmospheric oxidants such as hydrogen peroxide, ozone, hydroxyl radicals, sulfate radicals and sulfite radicals. The reactions take place in the bulk of solutions or on the gas–liquid interfaces and often are acid-catalyzed and/or enhanced by light. The review is appended by an experimental study of the aqueous-phase reaction of isoprene with nitrous acid (HONO). The decay of isoprene and formation of new products are demonstrated. The tentative chemical mechanism of the reaction is suggested, which starts with slow decomposition of HONO to NO2 and NO. The aqueous chemistry of isoprene explains the formation of a few tropospheric components identified by scientists yet considered of unknown origin. The reaction of isoprene with sulfate radicals explains formation of the MW 182 organosulfate found in ambient aerosol and rainwater while the reaction of isoprene with HONO explains formation of the MW 129 and MW 229 nitroorganic compounds identified in rainwater. Thus, aqueous transformations of isoprene should not be neglected without evidence but rather considered and evaluated in modeling of atmospheric chemical processes even if alternative and apparently dominant heterogeneous pathways of isoprene transformation, dry or wet, are demonstrated.

Improved accuracy and precision in δ15NAIR measurements of explosives, urea, and inorganic nitrates by elemental analyzer/isotope ratio mass spectrometry using thermal decomposition

Elemental analyzer systems generate N(2) and CO(2) for elemental composition and isotope ratio measurements. As quantitative conversion of nitrogen in some materials (i.e., nitrate salts and nitro-organic compounds) is difficult, this study tests a recently published method - thermal decomposition without the addition of O(2) - for the analysis of these materials. Elemental analyzer/isotope ratio mass spectrometry (EA/IRMS) was used to compare the traditional combustion method (CM) and the thermal decomposition method (TDM), where additional O(2) is eliminated from the reaction. The comparisons used organic and inorganic materials with oxidized and/or reduced nitrogen and included ureas, nitrate salts, ammonium sulfate, nitro esters, and nitramines. Previous TDM applications were limited to nitrate salts and ammonium sulfate. The measurement precision and accuracy were compared to determine the effectiveness of converting materials containing different fractions of oxidized nitrogen into N(2). The δ(13) C(VPDB) values were not meaningfully different when measured via CM or TDM, allowing for the analysis of multiple elements in one sample. For materials containing oxidized nitrogen, (15) N measurements made using thermal decomposition were more precise than those made using combustion. The precision was similar between the methods for materials containing reduced nitrogen. The %N values were closer to theoretical when measured by TDM than by CM. The δ(15) N(AIR) values of purchased nitrate salts and ureas were nearer to the known values when analyzed using thermal decomposition than using combustion. The thermal decomposition method addresses insufficient recovery of nitrogen during elemental analysis in a variety of organic and inorganic materials. Its implementation requires relatively few changes to the elemental analyzer. Using TDM, it is possible to directly calibrate certain organic materials to international nitrate isotope reference materials without off-line preparation.

4-Nitrophenol, 1-nitropyrene, and 9-nitroanthracene emissions in exhaust particles from diesel vehicles with different exhaust gas treatments

The dependence of nitro-organic compound emissions in automotive exhaust particles on the type of aftertreatment used was investigated. Three diesel vehicles with different aftertreatment systems (an oxidation catalyst, vehicle-DOC; a particulate matter and NOx reduction system, vehicle-DPNR; and a urea-based selective catalytic reduction system, vehicle-SCR) and a gasoline car with a three-way catalyst were tested. Nitro-polycyclic aromatic hydrocarbons (nitro-PAHs) and nitrophenols in the particles emitted were analyzed by thermal desorption gas chromatography/mass spectrometry and liquid chromatography/mass spectrometry. The secondary production of nitro-organic compounds on the filters used to collect particles and the adsorption of gaseous nitro-organic compounds by the filters were evaluated. Emissions of 1-nitropyrene, 9-nitroanthracene, and 4-nitrophenol in the diesel exhaust particles were then quantified. The NOx reduction process in vehicle-DPNR appeared to remove nitro-hydrocarbons efficiently but not to remove nitro-oxygenated hydrocarbons efficiently. The nitro-PAH emission factors were lower for vehicle-DOC when it was not fitted with a catalyst than when it was fitted with a catalyst. The 4-nitrophenol emission factors were also lower for vehicle-DOC with a catalyst than vehicle-DOC without a catalyst, suggesting that the oxidation catalyst was a source of both nitro-PAHs and 4-nitrophenol. The time-resolved aerosol mass spectrometry data suggested that nitro-organic compounds are mainly produced when an engine is working under load. The presence of 4-nitrophenol in the particles was not confirmed statistically because of interference from gaseous 4-nitrophenol. Systematic errors in the estimated amounts of gaseous 1-nitropyrene and 9-nitroanthracene adsorbed onto the filters and the estimated amounts of volatile nitro-organic compounds that evaporated during sampling and during post-sampling conditioning could not be excluded. An analytical method in which all gaseous compounds are absorbed before particles are collected, and in which the volatile compounds are derivatized, would improve the precision and the accuracy of the data.

Field measurement of nitromethane from automotive emissions at a busy intersection using proton-transfer-reaction mass spectrometry

Field measurements of seven nitro-organic compounds including nitromethane and ten related volatile organic compounds were carried out using proton-transfer-reaction mass spectrometry at a busy intersection of an urban city, Kawasaki, Japan from 26th February to 6th March, 2011. Among the nitro-organic compounds, nitromethane was usually observed along with air pollutants emitted from automobiles. The mixing ratios of nitromethane varied substantially and sometimes clearly varied at an approximately constant interval. The interval corresponded to the cycle of the traffic signals at the intersection and the regular peaks of nitromethane concentrations were caused by emissions from diesel trucks running with high speed. In addition to the regular peaks, sharp increases of nitromethane concentrations were often observed irregularly from diesel trucks accelerating in front of the measurement site. For other nitro-organic compounds such as nitrophenol, nitrocresol, dihydroxynitrobenzene, nitrobenzene, nitrotoluene, and nitronaphthalene, most of the data fluctuated within the detection limits.

The repertoire of nitrogen assimilation in Rhodococcus: catalysis, pathways and relevance in biotechnology and bioremediation

AbstractThe Rhodococcus genus exhibits diverse enzymatic activity that can be exploited in the conversion of natural and anthropogenic nitrogenous compounds. This catalytic response provides a selective advantage in terms of available nutrients while also serving to remove otherwise harmful xenobiotics. This review provides a critical assessment of the literature on bioconversion of organo‐nitrogen compounds with a consideration of applications in bioremediation and commercial biotechnology. By examining the major nitro‐organic compounds (amino acids, amines, nitriles, amides and nitroaromatics) in turn, the considerable repertoire of Rhodococcus spp. is established. The available published enzyme reaction data is coupled with genomic characterisation to provide a molecular basis for Rhodococcus enzyme activity with an assessment of the cellular properties that aid substrate accessibility and ensure stability. The metabolic gene clusters associated with the observed reaction pathways are identified and future directions in enzyme optimisation and metabolic engineering are assessed. © 2014 Society of Chemical Industry.

One-year study of nitro-organic compounds and their relation to wood burning in PM10 aerosol from a rural site in Belgium

Nitro-organic compounds were determined in a one-year set of atmospheric PM10 filter samples that were collected at a rural background site in Hamme, Belgium. In an earlier study, it was found that the site was substantially impacted by wood burning, making the filter samples appropriate for further investigations on wood burning indicators. In total, four groups of nitro-aromatic compounds (with molecular weights (MWs) of 139, 155, 169, and 183), α-pinene-related nitrooxy-organosulfates (MW 295), and the resin acid dehydroabietic acid (DHAA, MW 300) were quantified using liquid chromatography combined with negative ion electrospray ionization mass spectrometry. The annual mean concentrations were 0.94, 6.0, 7.7, 4.8, 7.8, and 1.76 ng m−3 for the sum of the nitrophenols (MW 139), 4-nitrocatechol (MW 155), the sums of the methyl-nitrocatechols (MW 169), of the dimethyl-nitrocatechols (MW 183), and of the α-pinene-related nitrooxy-organosulfates (MW 295), and DHAA (MW 300), respectively. 4-nitrocatechol, the sum of the methyl-nitrocatechols, and the sum of the dimethyl-nitrocatechols were substantially correlated with levoglucosan (r-values of 0.71, 0.66, and 0.65, respectively), consistent with their proposed origin from biomass burning. The nitro-aromatic compounds were also observed during the summer months, indicating a non-negligible usage of wood burning for domestic purposes at the site. The α-pinene-related nitrooxy-organosulfates (MW 295) were detected in high concentrations during the winter period, but they were poorly correlated with the biomass burning tracers. All of the targeted species showed a clear seasonal variation with highest concentrations in winter, followed by autumn, spring, and summer. Based on the DHAA measurements, it is suggested that burning of softwood is likely an important source for the formation of all the nitro-organic compounds measured.

Potential of zerovalent iron nanoparticles for remediation of environmental organic contaminants in water: a review

Zerovalent iron (ZVI) has the potential to degrade different organic contaminants. Nanoscale zerovalent iron (NZVI) can reduce the contaminants even more rapidly due to its small size and large specific surface area (SSA), compared to granular ZVI. The main objective of this paper is to assess and compare the potential of NZVI for degradation of different contaminants in water under specific environmental conditions. As a first step, the potential reactive functional groups/bonds associated with different contaminants are identified and possible reaction mechanisms are discussed. Thereafter, the reaction efficiencies of different organic contaminants with NZVI are compared. Mass of ZVI and reaction time required to transform a certain amount of contaminated water are calculated based on literature data. Sources of contaminants in the environment and their environmental occurrences are discussed to understand the potential locations where NZVI could be applied for removal of different contaminants. Overall it is observed that azo-compounds are readily transformed in the presence of NZVI particles. Reaction efficiencies of ZVI for reduction of nitro-organic compounds are also reasonably high. However, halogenated compounds with high molecular weights or complex structures (i.e., iodinated contrast media, DDT, polychlorinated biphenyls, etc.) show lower reaction rates with NZVI compared to the widely studied chlorinated hydrocarbons (i.e., trichloroethylene).

On-line measurements of gaseous nitro-organic compounds in diesel vehicle exhaust by proton-transfer-reaction mass spectrometry

Nitro-organic compounds, some of which cause adverse health effects in humans, are emitted in diesel engine exhaust. Speciation and quantification of these nitro-organic compounds in diesel engine exhaust particles have been extensively conducted; however, investigations into the emissions of gaseous nitro-organic compounds in diesel engine exhaust have not. In the present study, the properties of gaseous nitro-organic compounds in diesel engine exhaust were investigated through time-resolved measurement with a proton-transfer-reaction mass spectrometer and a chassis dynamometer. Three diesel trucks were tested, each with a different type of exhaust-gas treatment system (i.e., aftertreatment). Among the nitro-organic compounds detected, the emission of nitromethane was commonly observed and found to be related to the emissions of carbon monoxide, benzene, and acetone. The emission of other nitro-organic compounds, such as nitrophenol, depended on the vehicle, possibly due to the type of aftertreatment installed.

The Role of Stationary Phase Selection on Performance For Explosives Analysis Using GC-ECD

Gas chromatography with electron capture detection (GC-ECD) analysis of explosive-related nitro organic compounds was performed using four different column stationary phases with the focus being on their impact on analyte stability and transfer efficiency during analysis. All four columns used were 6 m x 0.53 mm, and the four stationary phases were a 1.0-microm thick 5% phenyl siloxane/95% methyl siloxane non-polar phase, a 1.5-microm thick 5% phenyl siloxane/95% methyl siloxane non-polar phase optimized for explosives analysis, an intermediate polarity 0.5-microm thick trifluoropropylmethyl siloxane phase, and a proprietary intermediate polarity 0.5-microm thick phase. Although all exhibited similar recovery (as defined as the detector signal per injected mass) when new, the intermediate polarity phases maintained higher sample recovery over the course of analyzing hundreds of samples than the non-polar phases, particularly for the nitramines hexahydro-1,3,5-trinitro-1,3,5-triazine and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, for which a 7x and 3x decrease in recovery were observed, and the nitrate esters nitroglycerin and pentaerythritol tetranitrate, for which a 7x and 11x decrease in recovery were observed. For most other explosive-related compounds, the differences in recovery were between 1.5x and 3x over the same course. Although the detailed chemical formulation of the stationary phases have not been disclosed by their manufacturers, we attribute the observed differences in performance to the stability of their passivation chemistries with regard to other mobile-phase compounds contained in complex field samples. Although these effects have been qualitatively noted in the past and in response, maintenance procedures have been developed to help account for this behavior, the analyst's preference is to use an explosives analysis method that does not require these time-consuming measures. Our desire to prolong this maintenance interval provided the motivation for the assessment reported in this paper. From our assessment, we conclude that manufacturers of GC columns should focus more attention on the stationary phase and passivation chemistries that can lead to the development of a column that is better able to maintain passivation against explosive compound degradation; and users intending to perform large numbers of analyses using GC-ECD should make this a consideration when selecting a column.

Theoretical study of the adsorption of 2-nitro-1-propanol on smectite surface models

Because their layered structure, high specific surface and natural occurrence, specifically in soils, clay minerals play an important role in the adsorption of pollutants, especially organic compounds. Different nitroorganic compounds are adsorbed in soils coming from pesticides, agrochemical and other different sources. Adsorption of nitrobenzene derivatives on phyllosilicates has been studied by experimental and theoretical techniques. In this work, the adsorption of 2-nitro-1-propanol on Na–smectite surface cluster models was theoretically studied at HF/6-31+G** and B3LYP/6-31+G** levels of theory. Three cluster models were designed in order to elucidate the different contributions of the mineral part of the system to the adsorption process, finding a very localized interaction between the adsorbate and the surface, mainly through an interaction between the NO 2 group with the surface cation and an hydrogen bond of the hydroxyl group with the basal oxygens; in addition, some weak CH…O and O…O interactions are also found. The adsorption energies have been estimated between −10 and −14 kcal/mol, depending on the model and level of theory. With Atoms In Molecules analysis the bonding structure of the Na + with the surface was characterized, finding the surface cation show four or five (3, −1) bond critical points with the oxygens of the surface (four for the interaction with the basal oxygens and one with the oxygen of the hydroxyl in the ditrigonal cavity). Adsorption process is able to produce some modifications in the geometry of the surface, increasing the rotation of the siloxane tetrahedral units, together with the vertical distance Na-surface, and the weakening of the Na⋯O hydroxyl interaction. All these facts suggest that the deformation of the surface is in part related with the bonding cation-surface.