Determination of Tocopherols and Vitamin A in Vegetable Oils Using Packed Capillary Column Supercritical Fluid Chromatography with Electrochemical Detection Francisco J. Senorans, Karin E. Markides, Leif Nyholm ˜ ´ Department of Analytical Chemistry, Uppsala Uni ersity, P.O. Box 531 SE-751 21 Uppsala, Sweden Received 28 September 1998; accepted 23 December 1998 Abstract: A recently developed microelectrochemical detector for packed capil- Ž . lary column supercritical fluid chromatography pcSFC has been applied to determine nanogram amounts of tocopherols and vitamin A in vegetable oil samples. With this procedure, no removal of triglycerides, preconcentration, or isolation of the unsaponifiable fraction of the sample was required. The oils could thus be injected with no sample preparation step and their tocopherol contents were determined in less than 20 min. The column used was an 80-cm 200- m-i.d. silica capillary with a packing of 5- mC particles, while the mobile phase was 18 supercritical carbon dioxide modified with 8% methanol. The amperometric detec- tor, based on a 25- m-diameter platinum microelectrode, was found to yield a better sensitivity than an on-column ultraviolet absorbance detector for the analy- sis of tocopherols and vitamin A. The amperometric detector was found to be compatible with pressure-programmed conditions using supercritical carbon diox- ide modified with methanol. The detection limit was determined to be 260 pg for oxidative detection of tocopherols and 240 pg for vitamin A. The experimental setup, including the microelectrode, could be employed for more than 300 injec- tions during several weeks of continuous use. 1999 John Wiley & Sons, Inc. J Micro Sep 11: 385 391, 1999 Key words: supercritical fluid chromatography; packed capillary columns; electro- chemical detection; tocopherols; itamins INTRODUCTION In open tubular column supercritical fluid chro- matography, the most frequently used mobile phase is pure carbon dioxide. However, in packed capillary column supercritical fluid chromatography, the use of carbon dioxide usually requires the addition of a polar modifier to deactivate remaining silanol groups on the packing material 1 . The utilization of or- ganic modifiers, apart from water, formamide, and formic acid 2 , impedes the use of a universal flame Ž . Ž . ionization detector FID and ultraviolet UV ab- sorbance or light scattering detection is therefore Correspondence to: L. Nyholm Contract grant sponsor: Swedish Natural Science Re- search Council; contract grant numbers K-1439-326 and K-AAKU 09368-320 Contract grant sponsor: Astra Hassle ¨ Contract grant sponsor: Ministerio de Educacıon y Cul- ´ Ž . tura, Spain postdoctoral fellowship usually employed in supercritical fluid chromatogra- Ž . phy SFC separations requiring other organic modi- fiers. In these cases, another possibility involves the use of amperometric detection, as was recently demonstrated on a bare platinum microelectrode in carbon dioxide modified with only small amounts of water 3 , acetonitrile, or methanol 4 . This micro- electrochemical detector has been shown to be com- patible with both oxidative and reductive detection, as well as pressure-programmed conditions in SFC, rendering good sensitivities and reproducibilities 5 . Other previously developed microelectrode assem- blies have made use of a combination of both mobile phase modifiers and supporting electrolytes 6, which may limit the stability of the chromatographic system, or have relied on microelectrodes covered with a conductive layer 7, 8 , which, however, seems to be incompatible with amperometric detection 9 . The aim of this article is to evaluate the perfor- mance of the previously described microelectro- Ž. Ž . J. Microcolumn Separations , 11 5 385 391 1999 1999 John Wiley & Sons, Inc. 385 CCC 1040-768599050385-07