A membrane extraction method for trace level phosphate analysis

Abstract

The concentration of phosphate in surface and oligotrophic waters is sometimes below the detection limit of conventional analytical methods. In this work, a membrane extraction method using a hydrophilic PTFE (H-PTFE) membrane filter was developed to detect trace level phosphate. Phosphoantimonyl-molybdenum blue (PAMB) was prepared under conventional conditions. The PAMB was made to react with hexadecyltrimethyl ammonium (HTMA) ions by ultrasonication in an ice bath to form an ion pair of PAMB and HTMA. The ion pair was entrapped on a H-PTFE filter by filtration, and the ion pair on the filter was extracted with CH₃CN. When 10 mL of CH₃CN was used as the extraction solvent for 100 mL of water sample (10 times of concentration factor), 0.80 μg PO₄ L⁻¹ (0.26 μg P L⁻¹) was successfully detected using a conventional spectrophotometer equipped with a 5 cm cell. The total phosphorus could also be detected after oxidation with potassium peroxosulfate.