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SummaryA simple dual-column gas chromatographic system with a six-port switching valve has been used to separate the atropisomers of PCB congeners 84, 91, and 95 in technical PCB formulations and in extracts of soil and river sediment. A capillary column coated with a methylphenylsiloxane stationary phase (CP-Sil8) was used as the first column, for retention window selection, and a permethylated P-cyclodextrin (ChirasilDex) capillary column as the main separation column. Because peak overlap could not be eliminated by optimization of column temperature, the enantiomeric ratios of PCB congeners could not be determined from the original chromatograms. The correct enantiomer ratio was determined from the peak areas obtained by deconvolution of the chromatograms. Whereas the PCB atropisomers considered were present in equal concentrations in the technical PCB formulations, analysis of a river sediment sample confirmed different residual concentrations of the atropisomers of congener 95.

SummaryAn improved optimization criterion has been introduced for computer assisted optimization of selectivity of two different capillary columns coupled in series and placed in two independently heated ovens. The suitability of this criterion, which incorporates the change of resolution power with the change of working conditions, has been verified by simultaneously tuning the temperatures of two columns differing in retention mechanism for separation of isomeric branched CB hydrocarbons.

Gas chromatographic study on chiral separation of PCBs was performed in a series of capillary columns coated with 0.1-µm film of modified cyclodextrin (CD) stationary phases. The preparation of columns included the investigation into the effect of the content of cyclodextrin derivative in polysiloxane, the type of polysiloxane and temperature of analysis on the quality of separation and retention of atropisomers of 15 selected PCB congeners. The separation properties towards PCBs of stationary phase heptakis(2,3-di-O-methyl-6-O-tert-butyl-dimethylsilyl)-␤-CD dissolved in SE-30, SE-54, and OV-1701, were compared with those of 6-monokis-octamethylene-permethyl-␤-CD anchored to polydimethylsiloxane polymer (ChirasilDex column, Chrompack, Middelburg, The Netherlands) and octakis(2,6-di-O-methyl-3-O-pentyl)-␥-CD in OV-1701 (MEGA, Legnano (MI), Italy). The correctness of quantitative enantiomer ratio determination was assesed by splitless analysis of PCBs reference solutions in concentration of 1.25-125 ng/ml (PCBs 45 and 91) and 2.5-250 ng/ml (PCB 95) (the PCB congeners are numbered according to IUPAC). Chirality 10: 540-547, 1998. © 1998 KEY WORDS: chiral capillary columns; PCB enantiomers; temperature dependence of enantioselectivity; effect of polysiloxane polarity on enantioselectivity; enantiomeric ratioGas chromatographic separation of polychlorinated biphenyls (PCBs) is based on the varying volatility and relatively low polarity of these compounds. PCBs are resistant enough to degradation, which, together with their lipophillic character, contributes to the persistence of PCBs in the environment and accumulation in living organisms. Toxicology studies of PCBs have pointed out the enantioselective character of their biological activity, 1 and possibly their biodegradation.Enantiomers of PCBs exist due to hindered rotation around single 1−1Ј C−C bond and are called atropisomers. The stability of atropisomers was documented by synthesis and subsequent separation of atropisomers of three polychlorinated biphenyls.2 It has been predicted that 19 of 78 PCB congeners, containing three or four chlorine atoms in ortho positions on phenyl groups, form stable enantiomers. 3Recent PCB atropisomers analyses were performed on stationary phases containing cyclodextrin (CD) derivatives in single or dual column systems. [4][5][6][7][8][9][10][11][12] The cyclodextrin derivatives used for analysis were mainly alkyl-or tertbutyldimethylsilyl-substituted. The experimental conditions reported for the single column separation [4][5][6][7][8]13 are reviewed in Table 1. An analysis of PCB atropisomers on ChirasilDex column 13 included the confirmation of the retention order by analysis of pure (+) and (−) atropisomers of PCB 84, 132, 135, 136, 174, and 176. The atropisomers were isolated by chiral RP-HPLC on permethylated CD.14 As reported for Chirasil-Dex column 7,9 containing 6-monokis-octamethylene-permethyl-␤-CD-polydimethylsiloxane, described in detail by Schmalzing et al., 15 and oktakis(2,6-di-O-methyl-3-O-pentyl)-␥-CD ...

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