Polar Degradation Products Research Articles

Aggregation behaviour of radiolytically degraded diglycolamide based solvent system

AbstractThe 0.1 M TODGA + 0.2 M DOHyA/n-DD phase was irradiated to various absorbed dose levels and the extraction behaviour of nitric acid and Nd(III) in the irradiated organic phases were studied. The organic phase was then subjected to dynamic light scattering studies to understand the aggregation behaviour in the organic phase. The results showed that the polar degradation products formed in the organic phase decreased the aggregation, while the higher homologue of n-DD enhanced aggregation.

Investigations on the unusual aggregation behaviour of tetra(2-ethyhexyl)diglycolamide in n-dodecane medium upon gamma irradiation

The limit of reverse micellar aggregation of amphiphilic ligands in n-dodecane medium, known as the third phase formation, is an undesirable event during the course of solvent extraction. The tetraalkyl diglycolamide (DGA) in n-dodecane (n-DD) is a promising solvent medium for the extraction of trivalent actinides from high-level nuclear waste, but it is susceptible to third phase formation. The DGAs in n-dodecane medium undergo a number of chemical transformations in organic phase, known as the radiolytic degradation products, when it was contacted with nuclear waste. While the effect of radiolytic degradation products on the solvent extraction behaviour of actinides was reasonably understood, the third phase formation and reverse micellar aggregation behaviour of the radiolytically degraded DGAs/n-DD has been not explored so far and unfamiliar to the solvent extraction community. To unravel the effect of radiolytic degradation on the aggregation behaviour(third phase formation) of DGAs in n-DD, the following categories of liquids comprising of (1) 0.2 M solution of tetra(2-ethylhexyl)diglycolamide (TEHDGA) present in n-DD, (2) TEHDGA alone, (3) n-dodecane alone, and (4) 0.2 M TEHDGA/n-DD in the presence of extracted nitric acid, were irradiated to a specified absorbed dose levels (10 kGy to 500 kGy) in a 60Co gamma irradiator. The irradiated liquids were made to a solution of 0.2 M TEHDGA in n-dodecane, if required, and the extraction behaviour of nitric acid in the irradiated organic phase was studied. The organic phase obtained after extraction was subjected to dynamic light scattering studies to explore the aggregation behaviour of TEHDGA in organic phase and compared with those obtained before extraction and irradiation. The results revealed that the formation of polar degradation products upon irradiation minimized the aggregation, and the production of higher homologs of n-paraffins enhanced aggregation. In reality, the formation of nitration and other polar radiolytic degradation products in organic phase, confirmed by FTIR spectroscopy, minimized the aggregation and therefore prevented the third phase formation to a significant extent in the present system.

An Insight into the Reactivity of the Electrogenerated Radical Cation of Caffeine

Controlled potential electrolyses of caffeine (CAF) were carried out at a Pt electrode in undried acetonitrile (ACN) and ACN-H2O and the products of the anodic oxidation were analyzed by HPLC-PDA-ESI-MS/MS. A higher current efficiency occurred in ACN-H2O, but an analogous chromatographic outline was found in both media, evidencing a reactive pathway of the electrogenerated radical cation CAF•+ with water, added or in trace, as nucleophile. No dimeric forms were evidenced, excluding any coupling reactions. Neither was 1,3,7-trimethyluric acid found, reported in the literature as the main oxidative route for CAF in water. Four main chromatographic peaks were evidenced, assigned to four proposed structures on the base of chromatographic and spectral data: a 4,5-diol derivative and an oxazolidin-2-one derivative were assigned as principal oxidation products, supporting a mechanism proposed in a previous work for the primary anodic oxidation of the methylxanthines olefinic C4 = C5 bond. Two highly polar degradation products were also tentatively assigned, that seemed generating along two different pathways, one opening the imidazolic moiety and another one opening the purinic one.

Noticeable Role of TFSI- Anion in the Carbon Cathode Degradation of Li-O2 Cells.

In this work we address the phenomena at the basis of the performance loss in a Li-O2 cell operating in the presence of a lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/tetraethylene glycol dimethyl ether (TEGDME) salt/solvent couple and a porous carbonaceous cathode. The cell was discharged/charged applying both voltage and capacity limits, and the effects of repeated galvanostatic cycling were addressed. The ex situ characterization of carbonaceous cathodes corresponding to different cutoff voltages was based on vibrational spectroscopies, transmission electron microscopy, and X-ray photoelectron spectroscopy. The reversible precipitation/decomposition of undesired products deriving from degradation of both carbon cathode and ethereal solvent is pointed out within a single voltage limited (2.0-4.6 V) discharge/charge cycle, whereas their irreversible accumulation on the surface of the electrode results after 100 capacity limited cycles. At the same time, the presence of polar degradation products (carbonates and carboxylates) at the cathode surface is accompanied by the buildup of a surface electric potential gradient, as revealed by differential binding energy shifts resulting from C 1s photoelectron spectra. This effect, seldom reported for Li-ion batteries, is for the first time put in evidence for a Li-O2 cell. Furthermore, the use of TFSI- anion is shown to lead to carbonate-based degradation products not involving the formation of Li2CO3. The peculiar occurrence of such degradation phenomena are attributed to the intrinsic low-donor number characteristic of the TFSI- anion.

A glass capillary based microfluidic electromembrane extraction of basic degradation products of nitrogen mustard and VX from water

In this work, a glass capillary based microfluidic electromembrane extraction (μ-EME) was demonstrated for the first time. The device was made by connecting an auxillary borosilicate glass tubing (O.D. 3mm, I.D. 2mm) perpendicular to main borosilicate glass capillary just below one end of the capillary (O.D. 8mm, I.D. 1.2mm). It generated the distorted T-shaped device with inlet ‘1’ and inlet ‘2’ for the introduction of sample and acceptor solutions, respectively. At one end of this device (inlet ‘2’), a microsyringe containing acceptor solution along with hollow fiber (O.D. 1000μm) was introduced. This configuration creates the micro-channel between inner wall of glass capillary and outer surface of hollow fiber. Sample solution was pumped into the system through another end of glass capillary (inlet ‘1’), with a micro-syringe pump. The sample was in direct contact with the supported liquid membrane (SLM), consisted of 20% (w/w) di-(2-ethylhexyl)phosphate in 2-nitrophenyl octyl ether immobilized in the pores of the hollow fiber. In the lumen of the hollow fiber, the acceptor phase was present. The driving force for extraction was direct current (DC) electrical potential sustained over the SLM. Highly polar (logP=−2.5 to 1.4) basic degradation products of nitrogen mustard and VX were selected as model analytes. The influence of chemical composition of SLM, extraction time, voltage and pH of donor and acceptor phase were investigated. The model analytes were extracted from 10μL of pure water with recoveries ranging from 15.7 to 99.7% just after 3min of operation time. Under optimized conditions, good limits of detection (2–50ngmL−1), linearity (from 5–1000 to 100–1000ngmL−1), and repeatability (RSDs below 11.9%, n=3) were achieved. Applicability of the proposed μ-EME was proved by recovering triethanolamine (31.3%) from 10μL of five times diluted original water sample provided by the Organization for the Prohibition of Chemical Weapons during 28th official proficiency test.

P-Tolyl isocyanate derivatization for analysis of CWC-related polar degradation products by mass spectrometry

Most of the precursors and/or degradation products related to the Chemical Weapons Convention (CWC) are polar. Identification of these molecules in environmental samples provides clues regarding the alleged usage and/or synthesis of the parent toxic chemicals. Such polar compounds need to be derivatized in order to analyze them by gas chromatography-mass spectrometry (GC-MS). In this study, we developed a new derivatizing reagent, para-tolyl isocyanate (PTI), for derivatization of polar CWC-related compounds. The PTI reagent selectively derivatizes the -OH and/or-SH functional groups with high efficiency, but does not react with carboxylic acid (-COOH) or phosphonic acid (-(O)P(OH)2) groups. The PTI derivatives of dialkyl aminoethanols, dialkyl aminoethanol-N-oxides, and 3-quinuclidinol were successfully eluted through GC, and their electron ionization (EI) mass spectra were distinct and provided the structure information by which the isomeric compounds can be easily distinguished. We also calculated the GC-retention index values that can be used for further confirmation of the target compounds. All the studied PTI derivatives can be analyzed by EI-MS with direct insertion probe and/or by direct electrospray ionization mass spectrometry (ESI-MS) together with the MS-MS data; both sets of data provide full structure information. The PTI reagent was found to be better in some respects than the conventional bistrimethylsilyl trifluoroacetamide (BSTFA), a trimethyl silylating reagent. The PTI reagent is commercially available, and the PTI derivatives are highly stable for months and are not sensitive to moisture. The applicability of the PTI derivatization for trace-level determination of the target CWC-related polar compounds in environmental matrices and in human plasma samples is also evaluated.

Ability of natural, acid-activated, and surfactant-modified Terra Rossa soils to sorb triazine herbicides and their degradation products

Two Terra Rossa soils that were collected in the Mediterranean region of Croatia and Turkey were tested in their natural, acid-activated, and surfactant-modified forms as sorbents for hydrophobic triazine groundwater pollutants in terms of their potential application to the multi-mineral landfill barriers. The soils were predominantly composed of kaolinite, followed by quartz, calcite, iron-bearing oxides/oxyhydroxides, and several other types of clay. The natural soils were poor in organic carbon (OC ≤2%), were similar in chemical composition, and were significantly different in their cation-exchange capacity (CEC). Sorption experiments were conducted with hydrophobic, weakly basic and ionisable triazine herbicides (atratone, ametryn, and atrazine) and three atrazine dealkylated degradation products. The Freundlich sorption parameters were evaluated and compared with respect to the physicochemical properties of the sorbates and sorbents. The low affinities of the natural soils for the sorption of all of the tested triazines were significantly enhanced by soil acid activation. The highest fractions of sorbed triazines were observed in the acid-activated soil with the higher CEC: 90% for the most basic and partially protonated atratone and ametryn and 78% and 61% for the more polar degradation products deisopropylatrazine and didealkylated atrazine, respectively. The enrichment of natural soils with OC by the sorption of the cationic surfactant hexadecyltrimethylammonium bromide (HDTMA) was more efficient in soil with higher CEC. The sorption intensities of all of the triazines except the most polar didealkylated atrazine increased significantly with increasing soil OC and correlated positively with the hydrophobicity of the compound. The sorption capacities of the HDTMA-modified soils were greater for most compounds than the capacities of the acid-activated soils. Based on the calculated sorbate fractions that were resistant to desorption, atratone and ametryn would be expected to be retained longest in the acid-activated soils, while the soil modification with HDTMA primarily prolonged the retention of ametryn and atrazine. The results indicated that, unlike natural Terra Rossa soils, their acid-activated or surfactant-modified forms could be applicable as components of an organophilic layer in multi-mineral barriers for retention of triazines and similar chemicals.

The influence of oxidation on the tribological performance of diester lubricant

ABSTRACTThe oxidative degradation test of di‐2‐ethylhexyl sebacate (DEHS) was carried out by a sealed stainless steel reactor. Fourier transform infrared spectroscopy and gas chromatography–mass spectrometry (GC–MS) were utilised to characterise the chemical composition and molecular structure of the oxidation products. The results revealed that 2‐ethyl‐1‐hexanol and mono(2‐ethylhexyl)sebacate were major degradation products in the liquid phase. Tribological behaviour was measured using a four‐ball tester. Scanning electron microscopy was employed to investigate the morphologies of the worn surface. Tribological results showed that anti‐wear and friction‐reducing performances of DEHS were highly dependent on the chemical composition of the oxidation products generated during the test. The hydroperoxides formed during the initial oxidation process could deteriorate lubrication properties of DEHS. However, certain amount of highly polar degradation products (acids and alcohols) generated could significantly improve the friction‐reducing performance of DEHS by the formation of boundary adsorption films on the rubbing surfaces. Copyright © 2013 John Wiley & Sons, Ltd.

Polar organic chemical integrative sampler (POCIS) uptake rates for 17 polar pesticides and degradation products: laboratory calibration

Polar organic chemical integrative samplers (POCIS) are useful for monitoring a wide range of chemicals, including polar pesticides, in water bodies. However, few calibration data are available, which limits the use of these samplers for time-weighted average concentration measurements in an aquatic medium. This work deals with the laboratory calibration of the pharmaceutical configuration of a polar organic chemical integrative sampler (pharm-POCIS) for calculating the sampling rates of 17 polar pesticides (1.15 ≤ logK(ow) ≤ 3.71) commonly found in water. The experiment, conducted for 21 days in a continuous water flow-through exposure system, showed an integrative accumulation of all studied pesticides for 15 days. Three compounds (metalaxyl, azoxystrobine, and terbuthylazine) remained integrative for the 21-day experiment. The sampling rates measured ranged from 67.9 to 279 mL day(-1) and increased with the hydrophobicity of the pesticides until reaching a plateau where no significant variation in sampling rate is observed when increasing the hydrophobicity.

O -Demethylation and Successive Oxidative Dechlorination of Methoxychlor by Bradyrhizobium sp. Strain 17-4, Isolated from River Sediment

O-Demethylation of insecticide methoxychlor is well known as a phase I metabolic reaction in various eukaryotic organisms. Regarding prokaryotic organisms, however, no individual species involved in such reaction have been specified and characterized so far. Here we successfully isolated a bacterium that mediates oxidative transformation of methoxychlor, including O-demethylation and dechlorination, from river sediment. The isolate was found to be closely related to Bradyrhizobium elkanii at the 16S rRNA gene sequence level (100% identical). However, based on some differences in the physiological properties of this bacterium, we determined that it was actually a different species, Bradyrhizobium sp. strain 17-4. The isolate mediated O-demethylation of methoxychlor to yield a monophenolic derivative [Mono-OH; 1,1,1-trichloro-2-(4-hydroxyphenyl)-2-(4-methoxyphenyl)ethane] as the primary degradation product. The chiral high-performance liquid chromatography (HPLC) analysis revealed that the isolate possesses high enantioselectivity favoring the formation of (S)-Mono-OH (nearly 100%). Accompanied by the sequential O-demethylation to form the bis-phenolic derivative Bis-OH [1,1,1-trichloro-2,2-bis(4-hydroxyphenyl)ethane], oxidative dechlorination of the side chain proceeded, and monophenolic carboxylic acid accumulated, followed by the formation of multiple unidentified polar degradation products. The breakdown proceeded more rapidly when reductively dechlorinated (dichloro-form) methoxychlor was applied as the initial substrate. The resultant carboxylic acids and polar degradation products are likely further biodegraded by ubiquitous bacteria. The isolate possibly plays an important role for complete degradation (mineralization) of methoxychlor by providing the readily biodegradable substrates.

Reduction of matrix effects and improvement of sensitivity during determination of two chloridazon degradation products in aqueous matrices by using UPLC-ESI-MS/MS

The development and validation of a sensitive and reliable detection method for the determination of two polar degradation products, desphenyl-chloridazon (DPC) and methyl-desphenyl-chloridazon (MDPC) in surface water, ground water and drinking water is presented. The method is based on direct large volume injection ultra-performance liquid chromatography electrospray tandem mass spectrometry. This simple but powerful analytical method for polar substances in the aquatic environment is usually hampered by varying matrix effects, depending on the nature of different water bodies. For the two examined degradation products, the matrix effects are particularly strong compared with other polar degradation products of pesticides. Therefore, matrix effects were studied thoroughly with the aim of minimising them and improving sensitivity during determination by postcolumn addition of ammonia solution as a modifier. An internal standard was used in order to compensate for remaining matrix effects. The calibration curve shows very good coefficients of correlation (0.9994 for DPC and 0.9999 for MDPC). Intraday precision values were lower than 5 % for DPC, 3 % for MDPC and the limits of detection were 10 ng/L for both substances. The method was successfully used in a national round robin test with a deviation between 3 and 8 % from target values. Finally, about 1,000 samples from different water bodies have been examined with this method in the Rhine and Ruhr region of North-Rhine-Westphalia (Germany) and in the European Union. Approximately 76 % of analysed samples contained measurable amounts of DPC at concentrations up to 8 μg/L while 53 % of the samples showed MDPC concentrations up to 2.3 μg/L.

Degradation of reactive dyes in wastewater from the textile industry by ozone: Analysis of the products by accurate masses

The present work describes the use of ozone to degrade selected reactive dyes from the textile industry and the analysis of the resulting complex mixture by liquid chromatography/mass spectrometry (LC–MS). To allow certain identification of the substances detected in the wastewater, the original dyes were also investigated either separately or in a synthetic mixture of three dyes (trichromie). Since the reactive dyes are hydrolyzed during the dyeing process, procedures for the hydrolysis were worked out first for the individual dyes. The ozonated solutions were concentrated by solid-phase extraction, which separated very polar or ionic substances from moderately polar degradation products. The latter, which are the primary degradation products, were investigated by liquid chromatography/mass spectrometry with a tandem quadrupole time-of-flight mass analyzer. Accurate masses, which in most cases could be determined with a deviation of ≤5 ppm from the exact value, were also measured. In addition, a diode-array detector was placed before the mass analyzer to provide UV–vis spectra of the products in the same run. With retention times, mass spectra, accurate masses, UV–vis spectra and, of course, knowledge of the structures of the original dyes, plausible structures could be proposed for most of the components of the moderately polar fraction. These structures were confirmed by 1H NMR in cases where it was practical to isolate the degradation products by preparative HPLC.

IDENTIFICATION, QUANTIFICATION AND DISTRIBUTION OF PAC-METABOLITES, HETEROCYCLIC PAC AND SUBSTITUTED PAC IN GROUNDWATER SAMPLES OF TAR-CONTAMINATED SITES FROM GERMANY

Four tar-contaminated sites in Germany (Lünen, Castrop Rauxel, Stuttgart and Wülknitz) were investigated and 42 polycyclic aromatic compounds (PAC) were detected in significant concentration ranges including polycyclic aromatic hydrocarbons (PAH), substituted PAC, heterocyclic PAC containing nitrogen, sulphur and oxygen as well as their metabolites. A similar composition and pattern of PAH heterocyclic PAC and metabolites were found in corresponding groundwater samples. Identification and quantification were performed using liquid-liquid extraction and analyses with gas chromatography – electron impact – mass spectrometry. Detailed investigation (in Castrop Rauxel, Germany) showed that the distribution of non-polar compounds can only be detected close to the source of contamination, whereas the distribution of more polar compounds and degradation products is more widespread downstream of an aquifer.

Characterization and quantification of biomarkers from biomass burning at a recent wildfire site in Northern Alberta, Canada

The composition of organic matter (OM) in pine vegetation and soil samples from a pine forest which was charred by a wildfire was analyzed using solid-state nuclear magnetic resonance ( 13C NMR) and gas chromatography–mass spectrometry (GC–MS) of solvent extracts to study the effects of thermal alteration on soil organic matter (SOM). The NMR data revealed the presence of unaltered biomolecules (cellulose, proteins) and low contents of aromatic C (15%) in the charred pine wood and cones while the charred soil samples exhibited higher contents of aromatic C (39–56%). The solvent extraction of charred and uncharred plant and soil samples yielded diterpenoids, triterpenoids, steroids, a series of aliphatic lipids, phenols and carbohydrates indicating the predominant input of higher plant OM and minor contributions from microorganisms and/or fauna. The lower yield of solvent extractable aliphatic lipids in the charred samples versus the uncharred samples suggests that these compounds are thermally degraded during a wildfire. Molecular markers for the burning of cellulose (levoglucosan, mannosan, galactosan) were detected in all charred samples. The comparison of charred and uncharred samples allowed the identification of unaltered pine derived biomolecules and their thermal alteration products in the charred samples. Terpenoid and steroid biomolecules were in part altered during incomplete combustion to aromatic, unsaturated and polar derivatives (“pyromolecules”) that still retained the characteristic skeleton of their precursors. Since some of the polar degradation products found in the charred soils can be generated either from thermal or microbial degradation, the aromatic and unsaturated hydrocarbon products are preferred as molecular markers for SOM burning. Ratios of biological precursors to aromatic (diterpenoids) or unsaturated products (steroids) indicate that the cyclic lipids in the pine wood and the soil surface horizon were highly altered. In conclusion, the solvent extractable lipids and carbohydrates in charred SOM are valuable, source-specific molecular markers for the burning of plant biomass and for tracing the biogeochemistry of charred residues in soils.

Optimization of Liquid Chromatography and Micellar Electrokinetic Chromatography for the Determination of Atrazine and its First Degradation Products in Humic Waters Without Sample Preparation

Liquid chromatographic method and micellar electrokinetic chromatographic method were optimized for determination of atrazine, desethylatrazine, desisopropylatrazine, hydroxyatrazine and their polar degradation products in solutions with humic acid without previous sample preparation step. Reversed-phase HPLC method was satisfactory in terms of repeatability and detection limits, which were ± 1.7–12.5% (RSD) and 0.1–0.5 mg L−1, respectively. However, the most polar products could not be separated from the front peak pertaining to humic acid. With MEKC, excellent separation of both chloro and hydroxy degradation products and parent compounds was achieved in a single analysis, and possible interferences of humic acid were successfully avoided by its retention at the anode. Drawbacks were detection limits, estimated to be 2–4 mg L−1, and RSD of the migration times was 20% compared to 0.5% with HPLC method. HPLC method was used to monitor degradation of atrazine and its first degradation products in the presence of humic acids, and MEKC was used for confirmation purposes.

Simultaneous determination of methyl tert.-butyl ether and its degradation products, other gasoline oxygenates and benzene, toluene, ethylbenzene and xylenes in Catalonian groundwater by purge-and-trap-gas chromatography–mass spectrometry

In Catalonia (northeast Spain), a monitoring program was carried out to determine methyl tert.-butyl ether (MTBE), its main degradation products, tert.-butyl alcohol (TBA), tert.-butyl formate (TBF), and other gasoline additives, the oxygenate dialkyl ethers ethyl tert.-butyl ether, tert.-amyl methyl ether and diisopropyl ether and the aromatic compounds benzene, toluene, ethylbenzene and xylene (BTEX) in 21 groundwater wells that were located near different gasoline point sources (a gasoline spill and underground storage tank leakage). Purge-and-trap coupled to gas chromatography–mass spectrometry was optimised for the simultaneous determination of the above mentioned compounds and enabled to detect concentrations at ng/l or sub-μg/l concentrations. Special attention was given to the determination of polar MTBE degradation products, TBA and TBF, since not much data on method performance and environmental levels are given on these compounds in groundwater. All samples analysed contained MTBE at levels between 0.3 and 70 μg/l. Seven contaminated hot spots were identified with levels up to US Environmental Protection Agency drinking water advisory (20–40 μg/l) and a maximum concentration of 670 μg/l (doubling the Danish suggested toxicity level of 350 μg/l). Samples with high levels of MTBE contained 0.1–60 μg/l of TBA, indicating (but not proving) in situ degradation of parent compound. In all cases, BTEX was at low concentrations or not detected showing less solubility and persistence than MTBE. This fact confirms the suitability of MTBE as a tracer or indicator of long-term gasoline contamination than the historically used BTEX.

Optimization of the class-selective extraction of triazines from aqueous samples using a molecularly imprinted polymer by a comprehensive approach of the retention mechanism

Direct, selective solid-phase extraction of triazines from aqueous samples is presented using a molecularly imprinted polymer (MIP) made with terbutylazine as template molecule. After optimization of the steps of the procedure, 14 triazines including degradation products were studied and satisfactory extraction recoveries were obtained except for thiotriazines. By comparing results obtained with the terbutylazine MIP and a similar non-imprinted polymer, it was determined that retention was achieved via specific interactions except for hydroxyterbutylazine. Selectivity of the extraction procedure was also verified by applying the MIP for the extraction of phenylureas that were not retained on it. The effects of the charge distribution and of molecular volume of the triazines (obtained by molecular modeling) on the selectivity of interactions between the analytes and the MIP were studied. However, when the optimized procedure was applied to real samples, low extraction recoveries were obtained due to strong matrix effects: ion-exchange occurs between the carboxylate groups of the MIP and the ionic species of the sample, that prevents subsequent specific interactions. By introducing an acid wash step, the procedure was successfully applied for the class-selective extraction of triazines from industrial effluent and surface water samples. Finally, increased extraction recoveries were achieved for the polar degradation products of triazines by using a mixed-phase composed of a polymeric sorbent and the MIP.

On the possible origin of humic matter in fine continental aerosol

In this paper we present a novel hypothesis for a possible formation mechanism of humic‐like substances, which were shown to be ubiquitous in fine continental aerosol. It tentatively relates the formation of atmospheric humic matter to the vast pool of soil organic matter via the evaporation, condensation, and aerosol‐phase polymerization of low molecular weight polar degradation products of organic debris in the soil. The theory is based on a comparative study on the chemical structure of bulk organic matter in fine aerosol and natural humic and fulvic acids and involves simplified mass flux calculations with estimated air‐water equilibrium data. Although the total soil flux of all degradation products is estimated to be of the order of ng m−2s−1, which is very low and difficult to measure, it is sufficient to sustain a mass concentration comparable to that of fine organic aerosol. The results imply that the proposed formation mechanism may be a significant natural source for fine organic aerosol at continental sites. We also suppose that precursors from other anthropogenic and natural sources contribute to producing secondary humic‐like polymeric matter in continental fine aerosol.

Alkaloid tolerance in Manduca sexta and phylogenetically related sphingids (Lepidoptera: Sphingidae)

Nicotine tolerance is well known for Manduca sexta. It also occurs in several other sphingids of the subfamilies Macroglossinae and Sphinginae. Only members of the subfamily Smerinthinae appear to be more susceptible to nicotine intoxication. Phylogenetic trees have been reconstructed from mitochondrial 16S rDNA and nuclear DNA to map nicotine tolerance.¶The nicotine binding site of both α-subunits of nicotinic acetylcholine receptors (nAChR) have been amplified and sequenced. No apparent amino acid substitution can be seen in the putative nicotine binding site of the α-subunits of nAChR from nicotine tolerant and nicotine sensitive sphingids. Thus, a simple target-site modification can be ruled out as a cause for nicotine tolerance. This finding agrees with feeding experiments: larvae of M. sexta and other sphingids of the Macroglossinae and Sphinginae not only tolerated nicotine, but also many other alkaloids that affect neuroreceptors other than acetylcholine receptors (nAChR, mAChR).¶Only 10 to 20% of nicotine injected into larvae of nicotine-tolerant taxa could be recovered later as free nicotine, nicotine N-oxide or cotinine, i.e., 80 to 90% must have been converted to polar conjugates or degradation products which are not detectable with the methods applied. Usually more than 98% of the recoverable alkaloids were found in the faeces. Excretion reached a maximum 6 h after injection in tolerant taxa. Larvae of Manduca sexta, which were reared on a nicotine-rich diet, showed higher nicotine degradation and faster nicotine elimination than naive larvae. Application of the cytochrome P450 inhibitor SKF 525A (proadifen) reduced the formation of nicotine N-oxide and the rate of alkaloid degradation. Thus, an inducible detoxification mechanism, coupled with a rapid and inducible excretion, appear to be a strategy in Sphingidae that helps them to live on host plants rich in otherwise toxic secondary metabolites.

Determination of triazine herbicides by capillary liquid chromatography with on-column focusing and temperature gradient

The combination of capillary liquid chromatography, temperature gradient and on-column focusing with large injection volumes offers a powerful tool for the determination of very low concentrations of triazines and their degradation products when very polar degradation products are present. A temperature gradient from subambient temperatures up to 70°C allows separation of eight triazines in 24 min. The focusing step makes it possible to increase 50 times the sample volume that can be injected into a capillary column. Detection limits (3×noise) are improved by a factor between 50 and 125 to 9 ng l −1 for hydroxyatrazine and 45 ng l −1 for atrazine. The chromatographic method, combined with solid phase extraction, was applied to the determination of eight triazines in ground water.