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RECEIVED for review August 4,1988. Accepted November 14, 1988.
Electrosynthesis of Chromatographic Stationary Phases Ge Hailin and G. G . Wallace* Chemistry Department, The University of Wollongong,P.O. Box 1144, Wollongong,New South Wales 2500, Australia
Polymerlc statlonary phases can be syntheslred on a range of substrates electrochmkally. For example, polypyrrde has been coated on vitreous carbon partlcles from a KCI solutlon electrochemlcally and used as a chromatographlc packing. The chemlcal and physlcal properties of polypyrrole/Cl on vitreous carbon have been Investlgated. Chromatogrephlc behavlor, lncludlng Ion exchange and reversed phase, has been found. The new polymeric material and column preparation technlques based on electrochemlcal polymerlzatlon may make these statlonary phases more stable, selective, and reproduclble and more easily prepared.
capillary or open tubular type columns. In each case the substrate employed to enable polymer growth should be mechanically stable as well as chemically inert and electrochemically conductive. For example, commercial carbon particles such as graphite or crushed reticulated vitreous carbon (RVC) have proven useful. Alternatively, metal substrates such as Pt, Au, some metal oxides, or even stainless steel may be employed. In the course of this work the feasibility of employing these polymers as stationary phases for ion-exchange or reversedphase chromatography has been established.
EXPERIMENTAL SECTION Polymeric materials have been widely used as stationary phases for gas and liquid chromatography due to their chemical and physical stability (1-4). Columns containing such polymers are usually prepared either by physical adsorption on a suitable support (e.g. silica or Celite) or by packing polymeric beads. The selectivity of such columns can be modified by varying the nature of the coating or the beads by copolymerization or by bonding appropriate functional groups to the polymer matrix. In recent times, electrochemical synthesis has proven useful for the synthesis of various polymers. Polymers such as polythiophene (5-7), polyaniline (8,9), polyfuran (6),and polypyrrole (10-14) have been successfully prepared. These polymers have previously been employed as sensors (15),energy storage devices (16),and semiconductors (17). Polypyrrole has, in particular, been intensively studied in recent years. The properties of this material make it ideal for preliminary studies into the electrochemical synthesis and application of new polymeric stationary phases. In this work, it has been established that electrochemical synthesis enables the following: (i) rapid and easily achieved column preparation; (ii) easy modification of the stationary phase; (iii) the production of a chemically and physically stable polymer; (iv) reproducible column production; (v) accurate control of stationary phase thickness and composition. It has also been demonstrated that the stationary phase can be grown either as beads (chemically or electrochemically) as a solid support for packed columns or on column walls for 0003-2700/89/0361-0198$01,50/0
Reagents and Standard Solutions. All reagents were of analytical reagent (AR)grade unless otherwise stated. LR grade pyrrole (Fluka) was redistilled before use. The aqueous solution used for polymer growth was 0.5 M KC1 and 0.5 M pyrrole. In some instances 0.1 M sodium dodecyl sulfate (SDS) was used as the supporting electrolyte for growing polymer. Acetate buffer was prepared by dissolving sodium acetate in water and then adjusting pH with acetic acid or sodium hydroxide. Methanol (HPLC grade) was obtained from BDH Chemicals. Water was distilled and then purified by a Milli-Q water system (Millipore). Instrumentation. All preliminary electrochemid experiments were performed by using a Princeton Applied Research (PAR) Model 173 potentiostat/gdvanostat in conjunction with a Model 179 digital coulometer and a Model 175 potential controller. HPLC experiments were conducted with a Waters Model M-6000 A chromatography pump in conjunction with a Model 450 variable wavelength detector. A cell for polymer plating on the particle substrates was designed in this laboratory and is described later. Polymer-coated particles (
