DETERMINATION OF POLYCHLORODIBENZOTHIOPHENES, THE SULFUR ANALOGS OF POLYCHLORODIBENZOFURANS, USING VARIOUS GAS-CHROMATOGRAPHIC MASS-SPECTROMETRIC TECHNIQUES

Polychlorodibenzothiophenes (PCDTs), the sulfur analogues of the polychlorodibenzofurans (PCDFs), were analyzed by gas chromatography/mass spectrometry (GC/MS). Various ionization (electron ionization (EI) and negative-ion chemical ionization (NCI) techniques and MS/MS experiments monitoring different daughter ions on a hybrid instrument were used to distinguish PCDTs from the polychlorodibenzodioxins (PCDDs) with the same nominal molecular mass. PCDTs were synthesized via direct chlorination of dibenzothiophene and via a novel thermal reaction of polychlorobiphenyls (PCBs) with elemental sulfur (displacement of two ortho Cl masses differing only by 0.0177 mass unit from those of the PCDDs, and high-resolution MS at resolutions of 18 000 or more would be required to resolve molecular ions of the PCDTs and PCDDs. EI fragmentation of the two compounds, however, is different with formation of M+ - 2Cl and M+ - COCl fragment ions from the PCDTs and PCDDs, respectively. QUAD MS/MS was highly selective for detecting PCDDs and PCDFs via reaction M+ --> (M - COCl)+, and MIKE MS/MS was valuable for detecting PCDTs via reaction M+ --> (M - 2Cl)+. In NCI, some PCDTs including 2,3,7,8-tetrachlorodibenzothiophene (2,3,7,8-tetra-CDT) showed high sensitivity with formation of stable dibenzothiophene anions, whereas the tetrachlorodibenzodioxins showed poor sensitivity. Various methods were applied to the analysis of environmental samples. Aquatic organisms (crabs, lobsters, and worms) from the Newark Bay area showed the presence of high levels of some PCDTs; in these samples, however, 2,3,7,8-tetra-CDT was not present.