A rapid, selective and sensitive cloud point extraction process using the nonionic surfactant, Triton X-114, to extract phosphorus in the form of orthophosphate from aqueous solutions was investigated. The method is based on the color reaction of orthophosphate with molybdate in acidic medium and in the presence of Sb(III) and ascorbic acid, then cloud point extraction of phosphomolybdenum blue in micellar medium. Effects of reaction and extraction parameters were studied and optimum parameters were established. The analytical characteristics of the method (e.g., limit of detection, linear range, relative standard deviation) were obtained. Linearity was obeyed in the range of 1.0-125 ng mL(-1) of P. The detection limit of the method was 0.5 ng mL(-1) of P. The interference effect of some common ions was also tested. The method was applied to the determination of orthophosphate in natural water samples. (C) 2009 Elsevier BY. All rights reserved.