Determination of trace phosphate ion with 3,3′,5,5′-tetramethylbenzidine using a flotation–extraction preconcentration method and spectrophotometric detection

A flotation–extraction method for sensitivity enhancement in spectrophotometry is proposed. The method is based on the reaction among molybdate, phosphate and 3,3′,5,5′-tetramethylbenzidine (TMB) in acidic medium to form an color charge transfer complex ion. It forms an ion associate with positive ions and floated at the water/benzene interface simultaneously, and then extracted by the DMSO-formic acid directly and determined by spectrophotometry. The proposed method is simple and convenient. The apparent molar absorptivity is 4.03×105 L mol−1 cm−1 at 458 nm. The proposed method has been applied to the determination of phosphate in wastewater with satisfactory results.