Anal. Chem. 1991, 63, 1210-1217
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Determination of Polychlorodibenzothiophenes, the Sulfur Analogues of Polychlorodibenzofurans, Using Various Gas Chromatographic/Mass Spectrometric Techniques Hans-Rudolf Buser* Swiss Federal Research Station, CH-8820 Wadenswil, Switzerland Christoffer Rappe
Institute of Environmental Chemistry, University of Umeil, S-90187 Umeil, Sweden
Polychlorodl~nzothlo~enes (PCDTs), the sulfur analogues of the polychlorodlbenzofurans(PCDFs), were analyzed by gas chromatography/mafo spectrometry (GWMS). Varlow, lonlzatkn (electron bnlzatbn (EI)and negatlvekn chemical lonlzatlon (NCI)) techniques and MS/MS experiments monltorlng dlfferent daughter Ions on a hybrid Instrument were used to dktlngukh PCDTs from the polychlorodlbenzodbxlns (PCDDs) wlth the same nominal molecular mass. PCDTs were synthesized vla dkect chlorhatlon of dlbenzothlophme and vla a novel thermal reactlon of polychloroblphenyls (PCBs) wlth elemental sulfur (dlsplacement of two ortho CI subetltuents by sulfur). The new compounds have molecular masses dlfferlng only by 0.0177 mass unlt from those of the PCDDs, and hlgh-resolutlon MS at resolutlons of 18000 or more would be requlred to resolve molecular Ions of the PCDTs and PCDDs. E1 fragmentath of the two compounds, however, Is dlfferent wlth formatlon of M+ - 2CI and M' COCl fragment Ions from the PCDTs and PCDDs, rwpectlvdy. QUAD MS/MS was hlghly selectlve for detecting PCDDs and PCDFs vla reactlon M' (M - COCI)', and MIKE MS/MS was valuable for detectlng PCDTs vla reactlon M' (M 2CI)'. I n NCI, some PCDTs Indudhg 2,3,7,8-tetrachlorodIbenzothlophene (2,3,7,8-tetra-CDT) showed hlgh sendtlvlty wtth formatkn of stable dlbenzothbphene anknr, whereas the tetrachlorodlbenzodloxlns showed poor sensltlvlty. Varlous methods were applled to the analyds of envlronmental samples. Aquatlc organlsms (crabs, lobsters, and worms) from the Newark Bay area showed the presence of hlgh levels of some PCDTs; In these samples, however, 2,3,7,8-tetra-CDT was not present.
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INTRODUCTION The presence of polychlorodibenzodioxins (PCDDs) and polychlorodibenzofurans (PCDFs; structures, see Figure 1) in environmental, biological, and a variety of industrial (incineration) samples has been widely reported (1-5). These compounds are present in many parts of the industralized world, and they are also detectable in the general human population (2, 4-6). In biological samples, including human tissue and milk, the toxic 2,3,7,8-substituted isomers are predominant (1-6).This occurrence has been of much scientific and public concern. The high toxicity of some of these compounds requires ultratrace analyses. A large number of studies have been initiated in recent years, many times targeted exclusively a t these two series of compounds. Generally, gas chromatography/mass spectrometry (GC/MS) is used for the detection and identification of these compounds. Recently, mass spectrometry/mass spectrometry (MS/MS) has also been applied (7,8). In these analyses, the mass spectrometers are 0003-2700/9 1/0363-1210$02.50/0
operated a t highest sensitivity and most of the time only a few ions or selected reactions, characteristic of PCDDs and PCDFs, are monitored. Other compounds present in a sample may thus escape detection. There have appeared reports on the presence of additional compounds related to PCDDs and PCDFs in some samples. Other halogenated (brominated and brominated/chlorinated) dibenzodioxins and dibenzofurans have been found in incineration samples and car emissions (9, lo),and in pyrolyzates of flame retardants (11). Methylated and other alkylated chlorodibenzofurans have been observed in sediment and sludge samples at pulp mills using chlorine bleaching (12).In this paper we report on the analysis of polychlorodibenzothiophenes (PCDTs; structure, see Figure l),the sulfur analogues of the PCDFs, and their occurrence in environmental samples. These new compounds were initially detected in aquatic organisms (crustaceans) from the New York Bight/ Newark Bay area because they responded at the m / z values used to monitor PCDDs, particularily in the analysis of 2,3,7,8-tetrachlorodibenzodioxin(2,3,7,8-tetra-CDD). Here we report on the microsynthesi of these new compounds and on various MS techniques including MS/MS for the identification and distinction of the PCDTs from the PCDDs and PCDFs. Finally, the application of these techniques to environmental samples will be described.
EXPERIMENTAL SECTION Materials and Reference Compounds. Sulfur, dibenzothiophene, various hexachlorobiphenyls, Aroclor 1254,and a seriea of PCDDs and PCDFs were from commerical sources. The PCBs were dissolved in methylene chloride (1-5 mg/mL), sulfur in carbon disulfide (10mg/mL). Sample Description and Sample Preparation. Aquatic samples (hepatopancreas of crabs and lobsters, and worms) were from the Newark Bay area near Elizabeth, NJ, and from Viiro, Sweden. Sample preparation was carried out for PCDDs and PCDFs according to standard procedures; this and the resulte on PCDDs and PCDFs have been previously described (13). The fractions containing the planar aromatic compounds were a n a l y d here. An extract of fly ash containing PCDDs and PCDFs from a municipal solid waste incinerator (MSWI) in Switzerland was obtained by courtesy of the Swiss Federal Institute for Material Testing and Research, Dubendorf, Switzerland. Synthesis of PCDTs via Chlorination of Dibenzothiophene. A series of PCDTs was prepared by chlorination of dibemthiophene. An aliquot of 1 mg of dibemthiophene (Fluka, Buchs, Switzerland) was dissolved in 500 FL of carbon tetrachloride; a few cryatals of anhydrous FeC&and 200 r L of chlorine solution (Clz bubbled in CCl, until a yellow-greenish solution, unknown concentration) were then added. The mixture was kept in the dark at room temperature with occasional shaking for 30 min. After reaction the solution was flash-evaporated (vacuum and slight heating). The residue was then extracted with a few portions of methylene chloride (total of 8 mL), which were p w e d through an alumina minicolumn (0.5 g of basic alumina in a Pasteur pipet). The eluate was concentrated and the residue 0 1991 Amerlcan Chemical Society
ANALYTICAL CHEMISTRY, VOL. 63, NO. 13, JULY 1, 1991
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Table 11. Congeners and Elution Temperatures Observed for the PCDTs from the Chlorination of Dibenzothiophene and from the Reaction of Aroclor 1254 with Sulfur
II
congener 111
IV
Figure 1. Structure of tetraCDFs ( I ) and tetraCDOs (11) and their SUM.. analogues, tetracDTs (111) and tetraCTAs (IV). The SUbstiMkn is notnecessaryYsy"eWcal. The PCDTs identified In this study have molecular masses very close to the FCDDs.
Table I. Ions and Reactions Monitored ( m / z Values) for Tetra-CDDs, Tetra-CDFs, and Tetra-CDTs
compds tetra-CDDs
tetra-CDFs
tetra-CDTs
[1aC,2]-tetra-CDDs
QUAD MS/MS and SIM MIKE MS/MS (ions monitored) (reactions monitored) 319.9 321.9 256.9 258.9 303.9 305.9 240.9 242.9 319.9 321.9 249.9 251.9 331.9 333.9
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319.9' 321.9' 319.9' 321.9' 303.9'
319.9' 321.9' 319.9+ 319.9' 333.9'
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319.9' 321.9' 257' 259' 241'
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319.9' 321.9' 241' 250' 270'
redissolved in 1mL of toluene. This solution, or a further dilution thereof, was used for GC/MS analysis. It consisted of a complex mixture of various PCDT congeners and isomers. Synthesis of PCDTs via the Thermal Reaction of PCBs with Sulfur. Aroclor 1254 and a series of hexachlorobiphenyls were thermally reacted with sulfur in separate quartz minivials (volume ca. 0.4 mL) in an electrical oven at 540-570 "C. The conditions were as previously described, with reaction periods of 60 s, of which 3-5 s were within 20 "C of the stated final temperature (14). Quantities of 100 pg of a PCB (20-100 pL of methylene chloride solution) and 100 pg of sulfur (10 p L of CS2 solution) were placed into the vials. After evaporation of the solvents the vials were flame-sealed with vacuum applied (
