Self-assembled monolayers of crown ethers for solid phase extraction in flow-injection analysis

Modification of a gold electrode with 2-[(6-mercaptohexyl)oxy]methyl-15-crown-5 yielded a self-assembled monolayer (SAM), CESAM, that preconcentrated Pb(II) from aqueous solution. With a 20 h modification, measurements by the copper underpotential deposition method showed that the fraction of the surface covered, Theta, was 0.99. Proof-of-concept was obtained for an analytical strategy in which the Pb(II)-CESAM was released into a flow stream by electrochemical oxidation of the gold thiolate and detected amperometrically. A detection limit of 6 pmol Pb(II) was estimated from the signal-to-noise ratio. Electrochemical release into a flow injection analysis system with detection by argon inductively coupled plasma spectroscopy provided detection of 0.2 nmol Pb(II) in a 200 muL injection. Analytical utility requires rapid, reproducible renewal of the CESAM. With 30-90 s modifications, Theta = 0.97 +/- 0.01 and was independent of modification time over that range. (C) 2003 Elsevier B.V. All rights reserved.