then combined with the sample extract, and concentrated to 5 ml. 

 The extracts were then transferred to a tandem arrangement of 

 silica gel columns containing activated silica gel, 44 percent 

 concentrated sulfuric acid on silica gel, and 33 percent IM 

 sodium hydroxide on silica gel. The purpose of these columns was 

 to remove acidic and basic compounds and easily oxidized 

 materials from the extracts. The silica gel support provided a 

 large surface area for contact with the sample extracts, thus 

 improving the cleanup efficiency. The PCDD/PCDF isomers were 

 eluted from the columns with 70 ml of hexane and the entire 

 eluates, including the original extract volume, were collected. 

 The hexane eluates were concentrated to 2-3 ml with a gentle 

 stream of nitrogen gas. 



Elemental sulfur, naturally occurring in sediments, was 

 removed by shaking with an aqueous solution of tetrabutylammonium 

 sulfite. The hexane solutions were dried with sodium sulfate and 

 chromatographed through columns containing approximately 5 g of 

 activated basic alumina with hexane/methylene chloride (97:3, 

 v/v) , and hexane/methylene chloride (1:1, v/v) as elution 

 solvents. The eluates were collected, concentrated to near 

 dryness and then diluted to 2 ml with hexane. Because the 

 sediment extracts were still highly colored and contained 

 precipitated material, the hexane solutions were chromatographed 

 through columns containing 1 g of activated florisil. The 

 columns were eluted with 15 ml of hexane, 25 ml of ethyl 

 ether/hexane (6:94, v/v) and 7 5 ml of methylene chloride/hexane 

 (3:1, v/v). The 3:1 methylene chloride/hexane eluates were 

 collected, concentrated to near dryness, and dissolved in 50 1 

 of n-decane containing 5 ng of an absolute recovery standard, 

 2,3,7,8-tetrachlorodibenzo-p-dioxin-^^Cl4 (2,3,7,8-tetra- 

 CDD--^^Cl4) . All solutions were stored at 0°C and protected from 

 light until analyzed. 



Analysis 



The extracts were analyzed and quantified for PCDD/PCDF 

 by combined capillary column gas chromatography/high resolution 

 mass spectrometry (HRGC/HRMS) . The HRGC/HRMS system consists of 

 a Carlo Erba Model 4160 gas chromatograph interfaced directly 

 into the ion source of a VG Model 7070 high resolution mass 

 spectrometer. The chromatographic column was a 60 M DB-5 fused 

 silica column. Helium was used as the carrier gas at a flow 

 velocity of 3 cm/sec. The mass spectrometer was operated in the 

 electron impact (EI) ionization mode at a mass resolution of 

 9,000-12,000 (M/ M, 10 percent valley definition). The operating 

 parameters of the HRGC/HRMS system are summarized in Table 1. 

 All HRGC/HRMS data were acquired by multiple-ion-detection (MID) 

 with a VG Model 11-250J Data System. The exact masses that were 

 monitored are shown in Table 3. 



