The gold surface of a quartz crystal microbalance was modified by the attachment of silica particles derivatised with N- [(3-trimethoxysilyl)propyl]ethylenediaminetriacetic acid. The device was employed to study the kinetics of the interaction of aqueous solutions of lead(ii) nitrate and silver(i) nitrate with the surface and for the selective separation of the metal ions.The quartz crystal microbalance (QCM) consists of a thin, circular, quartz crystal with circular gold electrodes placed centrosymmetrically on opposite faces. 1-5 Application of an electric field across the crystal, using an electronic oscillator, results in vibration of the crystal at its resonant frequency. The frequency of the oscillating crystal is decreased by deposition of mass on its surface and it has been shown that in the gas phase the change in frequency for a quartz crystal is related to change in mass by the Sauerbrey equation. 6 These devices are radially sensitive, i.e., it is the area under the gold electrode surface which is the most sensitive part, and the quartz surface projecting radially from the centre becomes less sensitive to mass deposited. 7 The mass sensitivity of the QCM has been exploited in both the vapour phase and in liquids, and there are numerous reported applications. [1][2][3][4][5][8][9][10][11][12][13][14][15][16] Two areas of the application of QCM devices are of immediate interest. The first involves the monitoring of biomolecular reactions in the liquid phase, in particular kinetic immunoassays which can be followed by the change in frequency as the mass on the surface of the crystal increases. 17 The piezoelectric device offers an alternative to the measurement of reaction kinetics of heterogeneous systems involving biomacromolecular interactions using the BIAcore TM instrument, although in the latter case the kinetic analyses have been more extensively investigated and developed. 18-20 Second, we are interested in the development of piezoelectric devices for the detection and determination of metal ions in solution, 14,[21][22][23][24][25][26][27] where sorbents chemically attached to the crystal are employed in order to obtain the selectivity required to determine one metal ion in the presence of others.We describe an application of the QCM which combines the two areas. The QCM device described in this work is not employed specifically as a mass sensor, in line with recent studies which question this aspect of their use, 28,29 but more so as an event sensor. A QCM device, derivatised with an aminopolycarboxylate ligand covalently attached to spherical silica particles, is employed in the search for selective substrates and/or conditions under which it would be possible to separate metal ions under flow conditions. A combination of the determination of an adsorption isotherm and investigation of association and dissociation phase kinetic parameters has been employed to permit the prediction of the behaviour of two metal ions on the derivatised silica substrate.

A quartz crystal microbalance modified by the attachment of silica particles derivatized with the aminopolycarboxylate ligand N- [(3trimethoxysilyl)propyl]ethylenediamine-N,NЈ,NЈ-triacetic acid has been employed to assess conditions under which mercury (II), lead (II), and silver (I) nitrates may be separated in aqueous solution. The separation protocol, which involved removal of Hg(II), as [HgI 4 ] 2Ϫ , and Pb(II) with H ϩ was successfully applied to a batchwise separation of the 3 metal ions.