Preparation of efficient packed columns with a polyperfluoroalkyl ether stationary phase

Activity coefficients of hydrocarbons at infinite dilution in di-n-octyltin dichloride. Comparison with results obtained in other alkyltin solvents

“…These authors semiquantitatively explained the surface properties of n-alkane + perfluoroalkane mixtures by assuming unitary surface activity coefficients and modeling the bulk activity coefficients by means of the regular solution or the Flory-Huggins approaches. Flory-Huggins interaction parameters, x*, were calculated with the equation [21] X* = In (RTp2 / KlP; M,) -In (v; / v¡) -1 + (M1 v* / M2v2) (6) where and p° represent the solute molecular weight and vapour pressure at the column temperature, respectively, M2 is the polymer number average molecular weight and v} and v¡ are the solute and the polymer specific "hard core" volumes, calculated by means of Flory state equation [22] using experimental thermal expansión coefficients. The interaction parameter is an adimensional free energy term that ineludes all the non-combinatorial contributions to excess free energy; Flory and collaborators [22] express x* as a sum of two contributions:…”

“…These properties have two important consequences in relation with their use as gas chromatographic stationary phases. On one side, as pointed out by Poole and collaborators [1,6,7], retention times in highly fluorinated stationary phases shall be shorter than in conventional phases, thus enabling the separation of low volatility or thermally labile substances.…”

“…Drastic improvements in the chromatographic behaviour is obtained by incorporating polar groups in the stationary phase molecules. The poly(perfluoroalkyl ether) phase Fomblin YR, [(OCFCF3CF2)n -(OCF2)mJ, was introduced in 1983 by Dhanesar and Poole [6,7]; paraffinic and olefinic hydrocarbons, injected at temperatures markedly lower than their boiling points, elute from these columns in short retention times, with very good peak shapes, but asymmetric peaks are obtained for solutes of higher polarity. Furthermore, the authors found that packings prepared by coating previously silylated supports (Gas-Chrom Q) gave symmetrical peaks when tested at low temperatures, but after heating to above 100 °C and retuming to low temperatures for re-testing, shorter retention times and asymmetric peaks were obtained, a behaviour that the authors attribute to film contraction, that results in bare surface exposition and liquid lenses.…”

“…Furthermore, the authors found that packings prepared by coating previously silylated supports (Gas-Chrom Q) gave symmetrical peaks when tested at low temperatures, but after heating to above 100 °C and retuming to low temperatures for re-testing, shorter retention times and asymmetric peaks were obtained, a behaviour that the authors attribute to film contraction, that results in bare surface exposition and liquid lenses. Columns stable at temperatures higher than 200 °C and with efficiencies similar to those obtained for conventional phases were obtained by coating Chromosorb P, packing the columns with coated support, and on-column silylating by injection of Silyl-8 or bis(trimethylsilyl)trifluoroacetamide (BSTFA) [6,7].…”

Support-deactivating fluorocarbon stationary phase for gas chromatography

“…However, these same weak intermolecular forces give rise to diminished retention in gas chromatography permitting the possibility of extending the technique to the separation of substances of higher-molecular-weight than is presently possible with conventional nonfluorinated phases. Recent research in the use of perfluorocarbon phases in gas chromatography has been directed toward their use for separation of fluorocarbon compounds (7,8), for the separation of involatile compounds at moderate temperatures (8, 9), and for the separation of polar organic compounds in aqueous solution (10). Several features in the above work are significant to this paper.…”