Using hydrogen bonding-specific interactions to detect water in aprotic solvents at concentrations below 50 ppm

The outstanding solvatochromic properties of the complex Ru(bpy)(CN)(4)(2-), deriving from the ability of the nitrile goup to participate in H-bond interactions, were explored to develop a sensor for low concentrations of water on common organic aprotic solvents. In dry solvents, the maximum wavenumber of the low energy transition of Ru(bpy)(CN)(4)(2-) presents linear correlations with the Kamlet-Taft solvent acidity parameter (slope = 0.59 +/- 0.02, r > 0.99) and Gutman acceptor number (slope = (1.7 +/- 0.1) x 10(-2), r > 0.99). The slopes and regression coefficients of the correlations measure the sensitivity of the compound to H-bond donation by the solvent and confirm its high specificity towards the sensing of H-bond donating solvents, such as water. In acetonitrile, tetrahydrofuran, N,N-dimethylformamide, dichloromethane and toluene, the sensor presents spectral changes that respond linearly to water concentrations in the range 5-70 ppm and compete favorably with the widely spread Karl-Fisher method with a detection limit of similar to 50 ppm. The high sensitivity and the much simpler spectrophotometric titration, portends the use of this complex as an optical water sensor for determination of low water contents in organic solvents. (c) 2005 Elsevier B.V. All rights reserved.