Evaluation of tetraalkylammonium tetrafluoroborate salts as high-temperature stationary phases for packed and open-tubular column gas chromatography

Abstract

Four tetraalkylammonium tetrafluoroborate salts were evaluated as high-temperature polar stationary phases for packed and open-tubular column gas chromatography. Tetrapropylammonium and tetraoctylammonium tetrafluoroborates were found to have too limited a temperature operating range to be generally useful. Tetrahexylammonium and tetrabutylammonium tetrafluoroborates had liquid ranges from 90 to 230 and 162 to 285°C, respectively, and were studied in more detail. Both phases showed strong, selective dipole interactions these being slightly stronger for the tetrabutylammonium salt than for the tetrahexylammonium salt. The tetrabutylammonium tetrafluoroborate salt also provided higher column efficiencies, by about a factor of two, when used in packed-column gas chromatography. Retention of a wide range of organic solutes was found to occur by gas—liquid partition on the tetrafluoroborate salts. Five surface roughening techniques were evaluated for the preparation of efficient, long-lived, open-tubular columns. Whisker-modified surfaces, alone or coated with a layer of microcrystalline sodium chloride, provided columns of acceptable efficiency (2000–2500 plates per meter) and greater durability than other column types. Barium carbonate-modified surfaces provided columns of the highest efficiency but of poor durability. Columns modified with a layer of Chromosorb R6470-1 were the least efficient and of poor durability. Examples of the separation of complex mixtures on packed and open-tubular columns, coated with tetraalkylammonium tetrafluoroborates, are given to illustrate their practical utility.