Fast-cycle trace analysis of dioxin in flue gas. Monitoring of the incineration of dioxin-containing waste from seveso

The fast trace analysis method used to monitor 2,3,7,8-TCDD in stack gas during the incineration of the waste from Seveso is described. The sampling of volatile organic compounds from flue gases, distributed between all three aggregation states, is based on a micromethod developed for the trace analysis of water using a specially dimensioned adsorptive charcoal filter (1.5 mg charcoal). In conjunction with subsequent GC/MS measurements the rapid “fast cycle trace analysis” ensured specific 2,3,7,8-TCDD detection down to 100 pg per m³ flue gas in cycle times of about 1–2 hours.     

Quantum chemistry study on the mechanism of the reaction between ozone and 2,3,7,8‐TCDD

Despite of its fundamental importance, the mechanism of the reaction between ozone and dioxins are still lack detailed investigation so far. It is well-known that quantum chemical calculation is a well-established method for investigating chemical reactions. In this article, quantum chemical calculation was employed to investigate the mechanism of the reaction between ozone and dioxins, as exemplified by 2,3,7,8-TCDD. The theoretical study showed that, 2,3,7,8-TCDD was gradually destructed by ozone via six cleavages of the CC bonds. All the six cleavages of the CC bonds were calculated and discussed in detail based on the theoretical calculations by the UB3LYP/6-31G(d) method. At the same time, the energies of stationary points along the reaction process were calculated by the UMP2/6-311g(d,p)//UB3LYP/6-31G(d) method and the activation energy was obtained. The obtained activation energy was 12.25 kcal/mol, which was lower than that of the reaction between benzene and O₃(16.64 kcal/mol). This indicated that, by comparison with benzene, 2,3,7,8-TCDD could be more efficiently destructed by O₃. The reason for this result was also discussed. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Theoretical study of structure, vibrational frequencies, and electronic spectra of polychlorinated dibenzo-p-dioxins

The structure, vibrational frequencies, and excited states of 2,3,7,8-tetrachloro-, 1,4,6,9-tetrachloro-, and octachlorodibenzo-p-dioxin (2,3,7,8-TCDD, 1,4,6,9-TCDD, and OCDD) were studied via complete active space SCF followed by the multireference second-order perturbative approach (CASSCF/CASPT2), as well as the time-dependent density functional theory (TD-B3LYP). The cc-pVDZ basis set and the full pi-electron active spaces of 16 electrons in 14 active orbitals were employed. Whereas 2,3,7,8-TCDD assumes a planar D(2)(h)() minimum, 1,4,6,9-TCDD and OCDD are slightly folded exhibiting the C(2)(v)() symmetry. The extra stabilization due to the folding is very small. In all three isomers the highly intensive band system in the 200-240 nm region is dominated by the transitions to the 2(1)B(2u) and 3(1)B(2u) states with by far the largest oscillator strengths. The low-intensity absorptions in the 280-320 nm region can be attributed to the 1(1)B(2u) <-- 1(1)A(g), with possible contribution of the vibronically allowed 2(1)A(g) <-- 1(1)A(g) transition. Both CASPT2 and TD-B3LYP convincingly predict 1(3)B(3g) to be the lowest lying triplet state, which contradicts the experimental assignments. Calculated harmonic wavenumbers and absorption spectra agree well with the experimental data, and are sufficiently distinct to allow for an unambiguous identification of the three isomers.     

Theoretical Study on Destruction Mechanism of 2,3,7,8-TCDD by O3 and NO3

In order to improve the destruction effciency of dioxins and also for developing new dioxin control technology, the destruction mechanisms of 2,3,7,8-tetrachlorodihenzo-p-dioxin (2,3,7,8-TCDD) by O₃ and NO₃, were investigated employing quantum chemical calcula-tions. For involved reactions, the microcosmic reaction processes were analyzed and de-picted in detail based on geometry optimizations made by the B3LYP/6-31G(d) method. At the same time, the reaction activation energies were also calculated at the MP2/6-311G(d,p)//B3LYP/6-31G(d) level. Configuration analysis indicated that 2,3,7,8-TCDD could be destroyed by O₃ and NO₃ in two different ways. The destruction of 2,3,7,8-TCDD by O₃ proceeded via the addition of O₃ and the cleavage of C=C while the destruction of 2,3,7,8-TCDD by NO₃ proceeded via the substitution of chlorine by NO₃. Calculated re-sults show that, the activation energy of the destruction reaction of 2,3,7,8-TCDD by NO₃ (267.48 kJ/mol) is much larger than that of the destruction reaction of 2,3,7,8-TCDD by O₃ (51.20 kJ/mol). This indicated that the destruction of 2,3,7,8-TCDD by O₃ is much more effcient than that of 2,3,7,8-TCDD by NO₃. The reason why the activation energy for the destruction reaction of 2,3,7,8-TCDD by NO₃ is so large, is also discussed.     

DFT calculations for the structure and properties of polychlorodibenzo-<Emphasis Type="Italic">para</Emphasis>-dioxine anion-radicals

Calculations for molecules and anion-radicals (ARs) of polychlorodibenzo-para-dioxines (PCDDs) in gas phase have been performed by Becke-Lee-Yang-Parr (B3LYP) hybrid method. The peculiarity of PCDD AR structure consists in the fact that one of C-Cl bonds is approximately by 0.75 Å longer than the other C-Cl bonds and is about 2.6 Å. A symmetric structure of 2,3,7,8-tetrachlorodibenzo-para-dioxine (TCDD) AR is the local minimum on the potential energy surface, which is higher than the absolute minimum by 2.76 kcal/mol. The electron affinity values were computed. PCDDs with one or two chlorine atoms have negative values of the electron affinity, while those with three or more chlorine atoms have positive ones.     

Bioassay (CALUX) measurements of 2,3,7,8-TCDD and PCB 126: Interference effects

Interference effects in CALUX measurements were studied. 2,3,7,8-TCDD and PCB 126 solutions were added, according to an experimental design, to the genetically modified cells. CALUX responses were measured for pure solutions of each of these pollutants, for their mixtures and for successive additions where the first added pollutant is removed after 4 h and replaced by medium solution, the same pollutant or the other one. It appeared that in cases where the cells were exposed to TCDD and PCB 126 in series, additivity was obeyed. This was not the case when the pollutants were added to the cells simultaneously as these results show antagonistic effects.     

Comparison of immunoaffinity column recovery patterns of polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans on columns generated with different monoclonal antibody clones and polyclonal antibodies

Evaluation of immunoaffinity columns (IACs) for dioxin serum sample clean-up requires a determination of the recovery of various dioxin congeners. We compared the IAC performance of different monoclonal and polyclonal anti-dioxin antibodies, measuring the recovery of congeners of polychlorinated dibenzo-p-dioxins (PCDDs). In addition, we measured the recovery of congeners of the structurally related polychlorinated dibenzofurans (PCDFs).The polyclonal antibody based IACs evaluated had lower recovery for highly chlorinated dioxin congeners, but were more specific toward 2,3,7,8-TCDD. The resemblance of the hapten to 2,3,7,8-TCDD appeared to play a clear role, but chlorines in the 2-, 3- and 7-positions of the hapten were essential. Recovery of 2,3,7,8-TCDD from the IAC showed some relation to the affinity for the antibody measured by either the K_a from accelerator mass spectrometry (AMS) or with 50% inhibition of color activity (IC₅₀) determined from an ELISA analysis.The IACs prepared from four monoclonal antibodies (Mabs) derived from a common hapten showed differences in their retention patterns of PCDDs/PCDFs. Comparison of IC₅₀ from ELISA with recovery from the IACs indicated that a minimum IC₅₀ of 100 ppb was required for satisfactory recovery from the IAC, but the correlation was poor, indicating other factors were involved. Mab DD3 showed the broadest spectrum of the Mabs and showed satisfactory recoveries of all of the dioxin congeners, except OCDD. In addition, DD3 showed good recovery toward 2,3,4,8-TCDF, 2,3,4,7,8-PeCDF and 2,3,4,6,7,8-HxCDF but has poor recovery when PCDFs have a chlorine substitution in the 1-position.     

Supercritical fluid extraction of 2,3,7,8-tetrachlorodibenzo-p-dioxin from sediment samples

Supercritical fluid extraction (SFE) is a promising technique for the extraction of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) from environmental matrices such as contaminated sediments. The ability of SFE to solubilize many organic contaminants is well documented in industrial processes but its analytical applications were exploited just recently. In this study supercritical carbon dioxide and nitrous oxide and their mixtures with 2% methanol were used to extract 2,3,7,8-TCDD from aquatic sediments. An attractive feature of this process is that the carbon dioxide, being a virtually inert fluid, leaves no solvent residue on the processed sediment. Almost 100% of the 2,3,7,8-TCDD can be extracted from a sediment spiked with 200 μg/kg 2,3,7,8-TCDD in 30 minutes by using supercritical carbon dioxide + 2% methanol. Cleanup procedure is compared with the Soxhlet extraction procedure currently used as a standard method for extracting dioxins from sediment samples.     

Reactions ofP-cyanospirophosphoranes with derivatives of phosphorous acid

5-Cyano-2,3,7,8-tetramethyl-1,4,6,9-trioxathia-5-phosphaspiro[4.4]nonane reacts with some chlorophosphites and amidophosphites to give the correspondingP ^III-cyano derivatives.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1669–1670, September, 1994.     

Reactions ofP-cyanospirophosphoranes with some thiols and alcohols

5-Cyano-2,3,7,8-tetrarnethyl-1,4,6,9-trioxathia-5-phosphaspiro[4.4]nonane reacts with thiols and secondary alcohols only in the presence of Et₃N.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 946–947, May, 1994.     

Mechanism for semiquinone formation in the oxygen negative chemical ionization mass spectrometry of 2,3,7,8-tetrachlorodibenzo-p-dioxin

The high toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) has led to the development of selective and highly sensitive quantitative methods for mass spectral analysis. Analytical selectivity has been demonstrated for the oxygen negative chemical ionization (ONCI) reaction of TCDD in an oxygen-rich plasma. While the reaction product (4,5-dichloro-1,2-benzoquinone anion) of 2,3,7,8-TCDD and oxygen is well known, the mechanism of its formation has not been studied thoroughly. In this report the results of a study involving the reaction of ¹⁸O₂ with 2,3,7,8-TCDD under high pressure and low pressure ONCI conditions are reported. A mechanism is proposed which is compatible with the observation that one ¹⁸O atom is incorporated into the product anion.     

Determination of 2,3,7,8-tetrachlorodibenzo-p-dioxin in commercial chlorophenols and related products

Summary We have recently published a procedure [1] which allows the selective determination of 2,3,7,8-TCDD in the presence of a large excess of other polychlorinated dibenzodioxins (PCDD) and polychlorinated dibenzofurans (PCDF). This method was applied for the determination of 2,3,7,8-TCDD in several samples of chlorophenols and related products.Analytical results are reported for pentachlorophenol, sodium pentachlorophenate, 2,3,4,5-tetrachlorophenol, 2,4-dichlorophenoxyacetic acid, hexachlorophene, and chloranil. While 2,3,7,8-TCDD could not be detected at a limit of detection of about 0.03 ng/g (ppb) in pentachlorophenol and chloranil, 2,3,7,8-TCDD could be shown to be present in all samples of sodium pentachlorophenate and also in the samples of 2,3,4,5-tetrachlorophenol, 2,4-D, and hexachlorophene. With the exception of 2,4-D, the concentration of 2,3,7,8-TCDD in these samples was below 1 ng/g (pbb).

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Bestimmung von 2,3,7,8-Tetrachlordibenzo-p-dioxin in handelsüblichen Chlorphenolen und verwandten Produkten

Zusammenfassung Ein von uns beschriebenes Verfahren [1] erlaubt die selektive Abtrennung von 2,3,7,8-TCDD von den übrigen PCDD und PCDF durch Fraktionierung an Alumina Woelm B Super I. Diese Methode wurde nun zur Bestimmung von 2,3,7,8-TCDD in verschiedenen Proben von Chlorphenolen und verwandten Produkten angewandt.Analysenergebnisse für Pentachlorphenol, Pentachlorphenol-Natrium, 2,3,4,5-Tetrachlorphenol, 2,4-Dichlorphenoxyessigsäure, Hexachlorophen und Chloranil werden berichtet. Während in Pentachlorphenol und Chloranil 2,3,7,8-TCDD bei einer Nachweisgrenze von ca. 0,03 ng/g (ppb) nicht nachgewiesen werden konnte, wurde 2,3,7,8-TCDD in allen übrigen Proben nachgewiesen. Mit Ausnahme von 2,4-Dichlorphenoxyessigsäure lagen die Konzentrationen an 2,3,7,8-TCDD unter 1 ng/g (ppb).

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This work was supported by the Ministerium für Ernährung, Landwirtschaft, Umwelt und Forsten, Baden-Württemberg. The skilful technical assistance of Roland Kerzenmacher and Heinz Tichaczek is acknowledged.     

Ab initio calculations on small hydrides including electron correlation

The two lowest electronic states (³ B ₁ and ¹ A ₁) of the methylene radical (CH₂) are calculated both in SCF-approximation and with the IEPA-PNO method (including electron correlation). The influence of polarization functions and electronic correlation on the shape of the potential curves of the two states is discussed. The calculated equilibrium geometries agree very well with experiment, but the results for transition energies (e.g. ³ B ₁¹ A ₁ excitation energy=9.2 kcal/mole, total binding energy=187 kcal/mole) are more reliable than the existent experimental values.     

Carbon–nitrogen bond dissociation energy values in C-nitrosocompounds

Measurements of the D(R? NO) bond strength in some C-nitrosocompounds have been made using an electron impact method. The appearance potential of the radical ion (R⁺) has been determined, the D(R? NO) bond energy being obtained from the relation The values obtained are: D(C₆H₅? NO) = 41 kcal/mole, D(t-C₄H₉? NO) = 34 kcal/mole, D(t-C₅H₁₁? NO) = 36 kcal/mole and D(i-C₃H₇? NO) = 36.5 kcal/mole. These values are in good agreement with the numerous estimations of Benson and coworkers and confirm that the C? N bond strength in C-nitrosocompounds is very much less than in nitrocompounds or in amines.     

The study of cis - and trans -2 butene using mass spectrometry

Using mass spectrometric technique, the effect of geometrical isomerism on the first and higher appearance energy values for C₄H₃ ⁺, C₄H₇ ⁺ and C₃H,₃ ⁺ ions obtained from cis-2-butene andtrans-2-butene is reported. The structure in the ionization efficiency curves (studied for 9 eV above threshold) for the same ions obtained from the two isomers is reported and compared. It is believed that at threshold C₄H₇ ⁺ fragment is formed from the two isomers as methallyl ion. For C₃H₃ ⁺ fragment formed from the cw-isomer at threshold the proposed structure is the propargyl ion with ΔH_f equal to 279-4 kcal/mole while for that ion obtained fromtransisomer the proposed structure is the allenyl ion with ΔH_f equal to 296.6 kcal/mole.     

Rapid determination of 2,3,7,8-tetrachlorodibenzo-p-dioxin in thermally treated soil

Summary Remedial action at an industrial site contaminated with chlorinated organic compounds including PCDD/PCDF involves thermal treatment of soil to reduce levels of 2,3,7,8-TCDD below a target value of 60 ng/kg. To guarantee the required quick turnaround for the analyses, a problem-oriented method was developed for the selective determination of 2,3,7,8-TCDD on a time scale of 2 – 4 h. Treated soil is extracted with an acidic solvent mixture (ethoxyethanol/toluene/6 mol/l sulphuric acid). The 2,3,7,8-TCDD in the extract is separated from matrix components and other PCDD/PCDF congeners by flash chromatography on alumina. The selectivity attained in this step allows final determination using isotope dilution GC/MS on a non-polar column. The method is in routine operation in an on-site laboratory. With a bench top quadrupole instrument, detection limits around 3 – 5 ng/kg are obtained. Previously: Institut biocontrol, now amalgamated with Institut Fresenius     

Selective determination of 2,3,7,8-tetrachlorodibenzo-p-dioxin in the presence of a large excess of other polychlorinated dibenzodioxins and polychlorinated dibenzofurans

Summary A procedure is described for the selective separation of 2,3,7,8-TCDD from all other PCDDs and PCDFs. For this purpose the mixture of PCDDs and PCDFs is fractionated on Alumina Woelm B Super I in such a manner that all PCDDs and PCDFs are eluted prior to 2,3,7,8-TCDD. This procedure allows a more sensitive quantitative determination of 2,3,7,8-TCDD in samples which contain 2,3,7,8-TCDD only as a very minor fraction of the other TCDDs or PCDDs and PCDFs. Determination of 2,3,7,8-TCDD in pentachlorophenol and in a waste sample from 2,4-dichlorophenol production by this procedure is described.

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Selektive Bestimmung von 2,3,7,8-Tetrachlordibenzo-p-dioxin in Gegenwart eines großen Überschusses anderer polychlorierter Dibenzodioxine und polychlorierter Dibenzofurane

Zusammenfassung Ein Verfahren wird beschrieben, das die selektive Abtrennung von 2,3,7,8-TCDD aus einer Mischung von allen PCDDs und PCDFs erlaubt. Dies geschieht durch Fraktionierung an Alumina Woelm B Super I, wodurch eine getrennte Elution aller PCDDs und PCDFs von 2,3,7,8-TCDD erreicht werden kann. Dieses Verfahren erlaubt die quantitative Bestimmung von 2,3,7,8-TCDD mit höherer Nachweisempfindlichkeit in Proben, die andere TCDDs bzw. PCDDs und PCDFs in extremen Überschüssen im Vergleich zu 2,3,7,8-TCDD enthalten. Am Beispiel der Bestimmung von 2,3,7,8-TCDD in Pentachlorphenol und in einem Produktionsrückstand von 2,4-Dichlorphenol wird die praktische Anwendbarkeit nachgewiesen.

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This work was supported by the Ministerium für Ernährung, Landwirtschaft, Umwelt und Forsten, Baden-Württemberg.The skilfull technical assistance of Roland Kerzenmacher is acknowledged.     

Specific features of the resonant electron attachment to the chlorodibenzo-p-dioxin molecules

The processes of resonant dissociative electron attachment to the molecules of dibenzo-p-dioxin and its chlorinated derivatives containing one to four chlorine atoms (totally eight compounds) were investigated. It was established that 2,3,7-trichlorodibenzo-p-dioxin; 1,2,3,4-tetrachlorodibenzo-p-dioxin; 1,3,7,8-tetrachlorodibenzo-p-dioxin, and 2,3,7,8-tetrachlorodibenzo-p-dioxin molecules are chatacterized by positive electron affinities. At electron energies below 2 eV, the electron attachment is caused by the shape resonances. Based on the energy correlation between the negative ion resonance peaks at 3—4 eV and the UV band maxima, it was suggested that electron attachment in this energy region occurs by the mechanism of inter-shell resonance with the molecular singlet-excited states as parents. The possibility for the rearrangement processes resulting in oxy-anionic structures to occur is substantiated.     

On the theory of processes in reaction centers of polyatomic molecules

Based on general principles of quantum theory of chemical transformations for polyatomic molecules, the notion of the reaction center (RC) was revised. The presence of RCs is a necessary condition for occurrence of all types of chemical transformations in complex systems. The physical picture of processes in RCs, conditions for maximum probability of transformations, the local character of a chemical reaction and its relation to the characteristic vibrations, and the methods of a priori search for RCs based on normal coordinate analysis of coupled states and on calculations of overlap integrals between vibrational wave functions were studied. Specific features of manifestation of characteristic vibrations in vibrational and vibronic spectra were investigated and the possibility of search for RCs using optical spectroscopy was considered. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1267–1273, August, 2006.     

Potential energy surface for Li+Li2: AN AB initio valence-bond calculation

A potential energy surface, calculated using the ab initio multistructure valence-bond technique, is reported for the collinear Li + Li₂ system. The ground state potential surface of the system is predicted to have no barrier to reaction and to possess a well of 4.62 kcal/mole (0.200 eV) relative to the infinitely separated reactants with the Li₂ at its equilibrium separation. An analytic potential energy surface is derived, which includes empirical corrections for the “diatomic” errors in the ab initio calculation. The empirically corrected surface dissociates to the experimental Li₂ potential energy curve when any one of the three lithium atoms is removed to a large distance. Cuts in the ab initio potential energy surface of the lowest electronically excited states of the system are also reported.