Coupled LC-GC-MS for on-line clean-up, separation, and identification of chlorinated polycyclic aromatic hydrocarbons at picogram levels in urban air

Role of hydrogen abstraction acetylene addition mechanisms in the formation of chlorinated naphthalenes. 2. Kinetic modeling and the detailed mechanism of ring closure

The dominant formation mechanisms of chlorinated phenylacetylenes, naphthalenes, and phenylvinylacetylenes in relatively low pressure and temperature (∼40 Torr and 1000 K) pyrolysis systems are explored. Mechanism elucidation is achieved through a combination of theoretical and experimental techniques, the former employing a novel simplification of kinetic modeling which utilizes rate constants in a probabilistic framework. Contemporary formation schemes of the compounds of interest generally require successive additions of acetylene to phenyl radicals. As such, infrared laser powered homogeneous pyrolyses of dichloro- or trichloroethylene were perturbed with 1,2,4- or 1,2,3-trichlorobenzene. The resulting changes in product identities were compared with the major products expected from conventional pathways, aided by the results of our previous computational work. This analysis suggests that a Bittner-Howard growth mechanism, with a novel amendment to the conventional scheme made just prior to ring closure, describes the major products well. Expected products from a number of other potentially operative channels are shown to be incongruent with experiment, further supporting the role of Bittner-Howard channels as the unique pathway to naphthalene growth. A simple quantitative analysis which performs very well is achieved by considering the reaction scheme as a probability tree, with relative rate constants being cast as branching probabilities. This analysis describes all chlorinated phenylacetylene, naphthalene, and phenylvinylacetylene congeners. The scheme is then tested in a more general system, i.e., not enforcing a hydrogen abstraction/acetylene addition mechanism, by pyrolyzing mixtures of di- and trichloroethylene without the addition of an aromatic precursor. The model indicates that these mechanisms are still likely to be operative.

Experimental and theoretical studies into the formation of C4-C6 products in partially chlorinated hydrocarbon pyrolysis systems: a probabilistic approach to congener-specific yield predictions

This work presents a study of the pyrolytic formation of vinylacetylene and benzene congeners formed from chlorinated hydrocarbon precursors, a complex, multipath polymerization system formed in a monomer-rich environment. (Co-)pyrolyses of dichloro- and trichloroethylene yield a rich array of products, and assuming a single dominant underlying growth mechanism, this (on comparing expected and observed products) allows a number of potentially competing channels to C4 and C6 products to be ruled out. Poor congener/isomer descriptions rule out even-carbon radical routes, and the absence of C3 and C5 products rule out odd-carbon processes. Vinylidenes appear unable to describe the increased reactivity of acetylenes with chlorination noted in our experiments, leaving molecular acetylene dimerization processes and, in C6 systems, the closely related Diels-Alder cyclization as the likely reaction mechanism. The feasibility of these routes is further supported by ab initio calculations. However, some of the most persuasive evidence is provided by congener-specific yield predictions enabled by the construction of a probability tree analogue of kinetic modeling. This approach is relatively quick to construct, provides surprisingly accurate predictions, and may be a very useful tool in screening for important reaction channels in poorly understood congener- or isomer-rich reaction systems.

Identification of organic compounds in atmospheric aerosol particles by on-line supercritical fluid extraction–liquid chromatography–gas chromatography–mass spectrometry

Atmospheric particles were collected with a high-volume sampling system at an urban site in Helsinki (Finland). The samples were analysed by on-line coupled supercritical fluid extraction-liquid chromatography-gas chromatography-mass spectrometry (SFE-LC-GC-MS). The aerosol sample was first extracted by SFE. The extract was then transferred to a liquid chromatograph where it was fractionated into four fractions according to polarity. Each fraction from the liquid chromatograph was transferred to a gas chromatograph by large-volume injection, where final separation was carried out. The first LC fraction (280 microl) contained nonpolar compounds, such as n-alkanes, hopanes and steranes. The second fraction (840 microl) included polycyclic aromatic hydrocarbons (PAHs) and alkyl-PAHs, while the third and fourth fractions (840 microl each) contained more polar compounds, such as n-alkan-2-ones, n-alkanals, oxy-PAHs and quinones.

On-line coupled liquid chromatography-gas chromatography

On-line coupled liquid chromatography-gas chromatography (LC-GC) is a powerful technique that combines the best features of LC and GC and is ideal for the analysis of complex samples. This review describes the unique features of on-line coupled LC-GC. The different interfaces and evaporation techniques are presented, along with their advantages and disadvantages. Guidelines are given for selecting a suitable LC-GC technique and representative applications are noted.

Lethality and EROD-inducing potency of chlorinated chrysene in chick embryos

Chrysene was non-specifically chlorinated and the toxic potency of the mixture formed was studied. The chlorinated mixture was considerably more potent than the parent compound in terms of embryolethality and EROD and AHH induction in a 2-week test in chick embryos. The chlorinated chrysene caused anomalies, including edema and beak defects, similar to those previously found after treatment of chick embryos with coplanar PCBs. Chlorinated chrysene was also much more potent than chrysene as an inducer of EROD in a 72-hour test in chick embryos in ovo and in chick embryo liver in vitro. It seems that the mechanism of toxicity of chlorinated chrysene in chick embryos is similar to that of the coplanar PCBs and other Ah receptor ligands. The effects of the chlorinated mixture were mainly accounted for by 6- chlorochrysene and 6,12-dichlorochrysene.