Development of solid phase micro-extraction (SPME) as a sample preparation technique for elemental speciation using high-performance liquid chromatography (HPLC) with ICP-MS detection

Solid phase micro-extraction (SPME), has advantages of simplicity, low cost, ease of use and rapid pre-concentration and extraction compared to other sample preparation techniques. The technique has found limited use in high performance liquid chromatographic applications because of the unavailability of fibers that are stable and durable in strong organic solvents. This study demonstrates two methods of fabricating SPME fiber coatings for HPLC applications.;The first method describes the preparation of fibers that are stable in strong organic solvents (xylene and methylene chloride) as well as acidic and basic solutions (pH 0.3 and 13) using the sol-gel process. The hydrolytic stability of these sol-gel prepared SPME fibers towards organic solvents and high and low pH solutions can be attributed to the fact that the coating is chemically bonded to the surface of the fused silica substrate. These fibers were subsequently used to extract organo-arsenic, organo-mercury and organo-tin compounds from aqueous solutions followed by separation using HPLC with UV absorbance detection. Under the experimental conditions used, detection limits of 80 mugL--1, 412 mugL--1 and 647 mugL--1 for triphenylarsine (Ph3As), diphenylmercury (Ph2Hg) and trimethylphenyltin (TMPhT) respectively, were obtained after extraction and HPLC separation.;The second method describes the fabrication of SPME fibers with poly(3methylthiophene) coated platinum micro-fiber electrodes. The fibers were fabricated by cycling the working electrode between --0.20 V and +1.7 V (vs. Ag/AgCl) in an acetonitrile solution containing 50 mM 3-methylthiophene monomer and 75 mM tetrabutylammonium tetrafluoroborate (TBATFB) electrolyte. All electrochemical procedures (extraction and expulsion) were conducted in a three-electrode system. After fabrication, the conducting polymer film was immersed in the sample solution and converted to its oxidized, positively charged form by applying a constant potential of +1.2 V with respect to Ag/AgCl reference electrode. Arsenate ions migrated into the film to maintain electro-neutrality. Upon subsequent reversal of the potential to --0.60 V vs. Ag/AgCl, the polymer film was converted to its reduced, neutral form and the arsenate ions were expelled into a smaller volume (200 muL) of de-ionized water for analysis using flow injection with inductively coupled plasma mass spectrometric (ICP-MS) detection.