Gas Chromatographic Enantiomer Separation of Atropisomeric PCBs Using Modified Cyclodextrins as Chiral Phases

Abstract

Columns containing different types of cyclodextrin derivatives have been evaluated for chiral gas chromatographic separation of atropisomeric PCBs, o,p9-DDT and o,p9-DDD. Separation was attempted on columns containing mixed chiral selectors, and the performance of two closely related selectors was also examined. The cyclodextrins were: permethylated-b-CD (PM-b-CD), heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-b-CD (2,3-M-6-TBDMS-b-CD), heptakis(2,3-di-O-methyl-6-O-tert-hexyldimethylsilyl)-b-CD (2,3-M-6-THDMS-b-CD), and heptakis(2,3-di-O-ethyl-6-O-tert-hexyldimethylsilyl)-b-cyclodextrin (2,3-E-6-THDMS-b-CD). The cyclodextrins were dissolved in OV-1701 or in a dimethylsiloxane/silarylene copolymer containing 5% phenyl in the backbone. The application of mixed chiral selectors led to improved separations, however; at most eleven PCB congeners were separated on a single column. Chiral resolution of o,p9-DDD was achieved. The use of a dimethylsiloxane/silarylene copolymer as a matrix for the cyclodextrins is a promising approach. With such a matrix, blocking of the CD cavities by silicone substituent groups can be avoided, and a reasonable CD solubility can be provided. The selectivity of heptakis(2,3-di-O-ethyl-6-O-tert-hexyldimethylsilyl)-b-CD and heptakis(2,3-di-O-methyl-6-O-tert-hexyldimethylsilyl)-b-CD was quite different, the former selector could separate four congeners, while the latter separated ten congeners.

Chiral separation of polychlorinated biphenyls using a combination of hydroxypropyl-γ-cyclodextrin and a polymeric chiral surfactant

“…However, only in few occasions chiral PCBs were separated. Separation of chiral PCBs are currently performed by capillary gas chromatography (GC) [3,[11][12][13][14].…”

“…König et al [13] resolved PCBs 45, 95 and 139 on a GC column coated with octakis(2,6-di-Omethyl-3-O-pentyl)-g-cyclodextrin. Magnusson et al [14] reported simultaneous GC enantioseparation of a mixture of nine chiral PCBs using a binary chiral selector containing permethylated-b-CD and heptakis (2,3-…”

A mixed stationary phase containing two versatile cyclodextrin-based selectors for the simultaneous gas chromatographic enantioseparation of racemic alkanes and racemic α-amino acid derivatives☆

“…Subsequently, in a number of papers the use of mixed binary CD selector systems for the enantioseparation of different classes of chiral compounds has been described [29][30][31][32][33][34][35]. In the present work, a comprehensive enantioselectivity spectrum toward racemic unfunctionalized alkanes and racemic derivatized ␣-amino acids as well as to other classes of racemic compounds such as lactones, diols, secondary alcohols, ketones and terpenes has been realized by diluting the two versatile CD selectors depicted in Fig.…”

Separation of Enantiomers by Gas Chromatography on Chiral Stationary Phases

“…Subsequently, in a number of papers the use of mixed binary CD selector systems for the enantioseparation of different classes of chiral compounds has been described [79,[100][101][102][103][104][105]. Recently, a comprehensive enantioselectivity spectrum toward racemic unfunctionalized alkanes and racemic derivatized α-amino acids as well as to other classes of racemic compounds, such as lactones, diols, secondary alcohols, ketones, and terpenes, has been realized by diluting the two versatile CD selectors octakis(6-O-methyl-2,3-di-O-pentyl)-γ-cyclodextrin (Lipodex G) [81] and heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin [87] in the polysiloxane PS-086 [106].…”

“…The possibility of determining the enantiomeric ratio of small chiral aliphatic oxiranes permitted study of the asymmetric epoxidation of simple unfunctionalized olefins and the kinetic resolution of racemic oxiranes by metal catalysts [116] and by microsomal enzymes [127,128]. Gas chromatographic capillary columns coated with modified CDs were used in enzyme and catalyst screening [129][130][131] and for the enantiomeric analysis of different classes of chiral compounds, such as essential oils, flavors and fragrances [86,87,[132][133][134], lactones [135], branched fatty acid esters [136,137], organochlorines [101,138], pollutants [139,140], silicon compounds [141], alkyl nitrates as atmospheric constitutents [110], inhalational anesthetics [142,143], compounds of clinical interest [144,145], α-amino acids for space exploration [146,147], as well as unfunctionalized 1,2-dialkylcyclohexanes [148] and aliphatic hydrocarbons [149][150][151] (see also references 97-105 in [10] and 270 references on pages 222-231 in the book of Schreier et al [16]). Pharmaceutical enantioseparations on Chirasil-Dex, although limited in scope, have also been described [152].…”