A simple and sensitive spectrophotometric flow method for determination of low concentrations of the flotation collector O-ethyldithiocarbonate (ethyl xanthate, CH(3)CH(2)-O-CS(2)(-)) in solutions is described. The method is based on ethyl xanthate detection at 301nm in medium of NaOH 50mmolL(-1). By injection of 200muL of sample, the analytical method shows linear response for the ethyl xanthate concentration from 0.5 up to 500mumolL(-1). Successive injections of 4mumolL(-1) ethyl xanthate (n=23) show a coefficient of variation lower than 0.6%, denoting high repeatability. The detection limit is 0.3mumolL(-1). At a flow rate of 2.0mLmin(-1), a frequency of 120injections/h of ethyl xanthate can be attained. By introduction of a tangential dialysis cell in the FIA system, the manual sample filtration step with 0.22mum filter was eliminated and the residual interference of suspended material, was completely overcome even for unfiltered sludge suspension samples, an important advantage that compensates for the frequency reduction to 25injections/h elevation and detection limit elevation to 2mumolL(-1), still outreaching for many applications. Potential applications of the method embrace the at line determination of ethyl xanthate in the ore processing industry, control of the concentration at its optimal level during the flotation process, as well as monitoring of residues in the effluents.