Long chain alkyl-polysiloxanes as non-polar stationary phases in capillary gas chromatography

Summary

A new methyl-octadecyl polysiloxane phase with a distinct selectivity in PCB separation and a significantly improved temperature range has been developed. The basic structural element of the separation of PCBs on methyl-octadecyl-polysiloxane is the elution according to the number of the substituents in the ortho-positions 2,2′ and 6,6′. The 2,2′,6,6′-substituted congeners are eluted first, while the non-2,2′,6,6′-substituted coplanar PCB are eluted last. As compared to methyl-phenyl (5%) polysiloxane (SE 54) the standard stationary phase used for the separation of the PCBs, the methyl-octadecyl-polysiloxane has several unique features in an improved PCB separation. The Sil 5–50% C18 column resolves the pair PCB 31/28 and also the sets PCB 5/8, PCB 16/15/32, PCB 25/53, PCB 48/47, PCB 56/60, PCB 118/149, PCB 105, 132, 153, and PCB 170/190. All these separations are not achieved with a SE 54 column. No separation is observed for the pair PCB 138/163 on Sil 5–50% C18. The order of elution of the Cl_xB congeners reveals a rather stringent structure correlation. If the structure/retention correlation is extended to all 209 Cl_xB congeners, 20 groups with one ring fixed / one ring variable substitution can be distinguished.