Rapid method for separating and quantifying orthophosphate and polyphosphates: application to sewage samples

A method was devised to separate and quantify the concentrations of orthophosphate and polyphosphates (tripolyphosphate and pyrophosphate) in sewage samples. Phosphate species were separated by anion exchange chromatography using Dowex 1-X8 resin (100–200 mesh, Cl− form). The use of a 0.2 M KCl/acetate buffer (pH 4.5) solution (100 mL) to elute orthophosphate and a 0.4 M KCl/acetate buffer (pH 4.5) solution (100 mL) to elute polyphosphates, quantitatively eluted phosphorus from the resin. Recoveries of 97±2% for orthosphosphate and 98±3% for polysphosphates were achieved for a variety of mixtures of orthophosphate, tripolyphosphate and pyrophosphate. Recoveries of orthophosphate and tripolyphosphate added to sewage were 95–97% and 88% respectively. The use of EDTA in eluents as used in previous studies was found to cause an interference when phosphorus was quantified using the phosphoantimonylmolybednum blue method. Analysis of centrifuged raw sewage samples revealed that phosphorus was present mainly as orthophosphate, no polyphosphates were detected. It is likely that polyphosphates are hydrolysed prior to entering sewers because of extreme pH and temperatures encountered during clothes and dishwashing or in sewers by bacteria or cations.