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Mass Number Figure 4. NCI mass spectrum of planar polychlorinated aromatic hydrocarbons isolated from Tittabawassee River (Michigan) carp
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Reagent gases were isobutane, methylene chloride, and oxygen. Only negative mass defect ions are shown. C-13 isotopes are eliminated for low intensity clusters
p-dioxin (TCDD) and that of the related tetrachlorodibenzofuran are well known. To screen for the presence of the planar polychlorinated aromatics using direct probe NCIMS, it is necessary to eliminate the nonplanar polychlorinated organics from the matrix. This requirement is imposed because the nonplanar polychlorinated organics in environmental samples, for example, those detected in the spectrum in Figure 3, exist in environmental samples at concentrations up to three orders of magnitude higher than the planar molecules. The total ionization in NCIMS is limited by space charge. That is, there is an absolute maximum to the number of ions that can exit the ion source for any set of ion source conditions. Therefore, if the mixture to be analyzed contains abundant quantities of compounds that produce intense negative ion mass spectra, these are the only compounds that will be seen. By removing the abundant components from the mixture, it is possible to detect orders of magnitude lower quantities of other components that are also present. We isolated these compounds by adsorption on activated carbon. The carbon was then washed with a solvent sequence to remove nonplanar polychlorinated organics and neutral lipids, and the planar polychlorinated organics were desorbed using toluene as a solvent. Figure 4 illustrates the NCI screening mass spectrum of an extract of carp that was obtained from the Tittabawassee River in Michigan adjacent to the Dow Chemical manufacturing facility. This spectrum indicates the presence of polychlornaphthalenes as oxygen exchange ions and a series of polychlordibenzodioxins (15). The mass spectrum in Figure 4 does not
CIRCLE 8 ON READER SERVICE CARD 634 A · ANALYTICAL CHEMISTRY, VOL. 53, NO. 4, APRIL 1981
accurately reflect the relative abundance of the specific dioxins in the mixture. The sensitivity of NCIMS for TCDD is lower than for any of the other tetrachlorodioxin isomers, and it is also lower than the sensitivity of NCIMS for the higher chlorinated dioxins. The confirmation that the tetrachlorodioxin that appears at m/e 301 in the spectrum in Figure 4 is in fact the 2,3,7,8 isomer has been obtained by capillary gas chromatography, with both positive and negative ion detection (15,16). In a survey of fish samples taken from freshwater sources in the Midwest and Northeast for planar polychlorinated organics, we were able to detect polychlorinated naphthalenes (Halowax) in every fish sample. Polychlorinated dibenzofurans were detected in extracts of fish that contained concentrations of polychlorobiphenyls exceeding 2.5 ppm. The polychlorinated dibenzodioxins illustrated in Figure 4 were detected only in samples of fish taken from the Tittabawassee River. It seems highly unlikely that the trace chemistry of ordinary combustion is responsible for this dioxin contamination (17). We have been interested in screening human seminal plasma for the presence of toxic substances because of observations in the literature that suggest that male fertility potential in the U.S. has decreased during the past 30 years (15,18,19). Figure 5 illustrates the 12C negative mass defect ions that appeared in the NCI mass spectrum of an extract of human seminal plasma that was obtained using steam distillation with continuous liquid-liquid extraction as the clean-up procedure (14). This spectrum showed evidence of the presence of polychlorobenzenes, polychlorophenols, poly-
