A novel approach to investigations of radical ion reactions in solutions using the delayed fluorescence quenching caused by reactions of radical ions in the course of their geminate recombination was proposed. To determine the reaction rate constants, the ratios of fluorescence decays, obtained at different quenchers concentrations, were analysed. The approach was applied to study reactions of hexadecane radical cations with a number of electron and proton acceptors. The maximum rate constant of about 4 x 10(10) M-1 s(-1) was obtained and this value was found to be the diffusion-controlled limit in n-hexane solutions at room temperature. (C) 2004 Elsevier B.V. All rights reserved.