Trace Analysis of Phosphate Ion by Dispersive Liquid-liquid Microextraction Based on the Ion-pair Formation with Methyltrioctylammonium Chloride

A simple and efficient dispersive liquid-liquid microextraction (DLLME) method coupled with microvolume UV-vis spectrophotometry was developed for the determination of trace amounts of phosphate. This method is based on the formation of phosphomolybdate due to the reaction between molybdate and phosphate followed by its reduction with stannous chloride in aqueous sulfuric acid medium. The blue product was converted into its ion-pair with methyltrioctylammonium chloride (Aliquat-336) and then extracted into an organic solvent (carbon tetrachloride) dispersed in aqueous solution. The factors influential to this procedure, such as concentration of sulfuric acid, ammonium molybdate and Tin(II) chloride in the sample solution, amount of methyltrioctylammonium chloride, volume of extraction solvent and reaction time were investigated and optimized. Under optimum conditions, the linear range was found to be 50-6500 ng mL-1 for phosphate, and the limit of detection to be 12 ng mL-1. The proposed method has been applied for the determination of trace amounts of phosphate in different water and wastewater samples and satisfactory results were obtained.