Selective determination of orthophosphate and total inorganic phosphates in detergents by flow injection photometric method

A flow injection photometric system was developed for the determination of orthophosphate and total inorganic phosphates in detergents. While orthophosphate was directly determined in the presence of other phosphates by utilizing the kinetic discrimination of flow injection analysis, total inorganic phosphates was analyzed after on-line hydrolysis of polyphosphates in 2.5 mol l−1 sulfuric acid for 50 s under 145°C. Sodium dodecyl sulfate (SDS) was added to mask the interference of non-ionic surfactants. The detection limits and the sampling rates were 2.5 mg l−1 P2O5 and 40 h−1 for total inorganic phosphates, and 1.0 mg l−1 P2O5 and 80 h−1 for orthophosphate determination. The proposed method was applied to analyze orthophosphate and total inorganic phosphates in washing powders. The experimental results are in good agreement with those obtained by the Chinese national standard methods.